feat(es/minifier): Implement more rules (#1871)

swc_ecma_codegen:
 - Fix codegen of `U+0028` and `U+0029`. 

swc_ecma_minifier:
 - Implement MVP.

swc_ecma_transforms_base:
 - `fixer`: Handle seq/await in rhs of for-of.

.github/workflows/cargo.yml

@@ -160,7 +160,7 @@ jobs:
       # Source map format
       - uses: actions/setup-node@v2
         with:
-          node-version: "14"
+          node-version: "16"
 
       # We explicitly do this to cache properly.
       - name: Install Rust
@@ -170,7 +170,7 @@ jobs:
 
       - uses: actions/setup-node@v2
         with:
-          node-version: 14
+          node-version: 16
 
       - uses: denoland/setup-deno@v1
         with:

Cargo.lock

@@ -2430,7 +2430,7 @@ dependencies = [
 
 [[package]]
 name = "swc_ecma_codegen"
-version = "0.64.0"
+version = "0.64.2"
 dependencies = [
  "bitflags",
  "num-bigint",
@@ -2500,11 +2500,12 @@ dependencies = [
 
 [[package]]
 name = "swc_ecma_minifier"
-version = "0.14.0"
+version = "0.15.0"
 dependencies = [
  "ansi_term 0.12.1",
  "anyhow",
  "fxhash",
+ "indexmap",
  "log",
  "once_cell",
  "pretty_assertions 0.6.1",
@@ -2522,7 +2523,9 @@ dependencies = [
  "swc_ecma_transforms_base",
  "swc_ecma_utils",
  "swc_ecma_visit",
+ "swc_node_base",
  "testing",
+ "unicode-xid",
  "walkdir",
 ]
 
@@ -2605,7 +2608,7 @@ dependencies = [
 
 [[package]]
 name = "swc_ecma_transforms_base"
-version = "0.24.0"
+version = "0.24.1"
 dependencies = [
  "fxhash",
  "once_cell",
@@ -2788,7 +2791,7 @@ dependencies = [
 
 [[package]]
 name = "swc_ecma_transforms_typescript"
-version = "0.30.0"
+version = "0.30.1"
 dependencies = [
  "fxhash",
  "serde",
@@ -2835,7 +2838,7 @@ dependencies = [
 
 [[package]]
 name = "swc_ecmascript"
-version = "0.48.0"
+version = "0.49.0"
 dependencies = [
  "swc_ecma_ast",
  "swc_ecma_codegen",
@@ -2940,7 +2943,7 @@ dependencies = [
  "env_logger 0.7.1",
  "log",
  "once_cell",
- "pretty_assertions 0.6.1",
+ "pretty_assertions 0.7.2",
  "regex",
  "swc_common",
  "testing_macros",

ecmascript/Cargo.toml

@@ -6,7 +6,7 @@ edition = "2018"
 license = "Apache-2.0/MIT"
 name = "swc_ecmascript"
 repository = "https://github.com/swc-project/swc.git"
-version = "0.48.0"
+version = "0.49.0"
 
 [package.metadata.docs.rs]
 all-features = true
@@ -34,7 +34,7 @@ typescript = ["typescript-parser", "swc_ecma_transforms/typescript"]
 swc_ecma_ast = {version = "0.49.0", path = "./ast"}
 swc_ecma_codegen = {version = "0.64.0", path = "./codegen", optional = true}
 swc_ecma_dep_graph = {version = "0.33.0", path = "./dep-graph", optional = true}
-swc_ecma_minifier = {version = "0.14.0", path = "./minifier", optional = true}
+swc_ecma_minifier = {version = "0.15.0", path = "./minifier", optional = true}
 swc_ecma_parser = {version = "0.65.0", path = "./parser", optional = true, default-features = false}
 swc_ecma_transforms = {version = "0.61.0", path = "./transforms", optional = true}
 swc_ecma_utils = {version = "0.41.0", path = "./utils", optional = true}

ecmascript/codegen/Cargo.toml

@@ -7,7 +7,7 @@ include = ["Cargo.toml", "src/**/*.rs"]
 license = "Apache-2.0/MIT"
 name = "swc_ecma_codegen"
 repository = "https://github.com/swc-project/swc.git"
-version = "0.64.1"
+version = "0.64.2"
 
 [dependencies]
 bitflags = "1"

ecmascript/codegen/src/lib.rs

@@ -2543,6 +2543,13 @@ fn escape_without_source(v: &str, target: JscTarget, single_quote: bool) -> Stri
                 let _ = write!(buf, "\\x{:x}", c as u8);
             }
 
+            '\u{2028}' => {
+                buf.push_str("\\u2028");
+            }
+            '\u{2029}' => {
+                buf.push_str("\\u2029");
+            }
+
             _ => {
                 buf.push(c);
             }

ecmascript/codegen/src/tests.rs

@@ -560,7 +560,7 @@ fn test_escape_without_source() {
     es2020("abcde", "abcde");
     es2020(
         "\x00\r\n\u{85}\u{2028}\u{2029};",
-        "\\x00\\r\\n\\x85\u{2028}\u{2029};",
+        "\\x00\\r\\n\\x85\\u2028\\u2029;",
     );
 
     es2020("\n", "\\n");

ecmascript/minifier/.eslintrc

@@ -0,0 +1,47 @@
+{
+    "parser": "babel-eslint",
+    "rules": {
+        "indent": [
+            "error",
+            4
+        ],
+        "semi": [
+            "error",
+            "always"
+        ],
+        "space-unary-ops": 2,
+        "no-undef": "off",
+        "consistent-return": "off",
+        "no-prototype-builtins": "off",
+        "no-cond-assign": "off",
+        "multiline-ternary": [
+            "error",
+            "always-multiline"
+        ],
+        "object-property-newline": [
+            "error",
+            {
+                "allowAllPropertiesOnSameLine": false
+            }
+        ],
+        "function-call-argument-newline": [
+            "error",
+            "always"
+        ],
+        "object-curly-newline": [
+            "error",
+            "always"
+        ],
+        "comma-dangle": [
+            "error",
+            "always"
+        ],
+        "function-paren-newline": [
+            "error",
+            "always"
+        ],
+        "no-trailing-spaces": [
+            "error"
+        ]
+    }
+}

ecmascript/minifier/.gitignore

@@ -0,0 +1,2 @@
+# Used to see ideal output using terser
+lab.js

ecmascript/minifier/Cargo.toml

@@ -7,13 +7,14 @@ include = ["Cargo.toml", "src/**/*.rs", "src/lists/*.json"]
 license = "Apache-2.0/MIT"
 name = "swc_ecma_minifier"
 repository = "https://github.com/swc-project/swc.git"
-version = "0.14.0"
+version = "0.15.0"
 
 [features]
 debug = []
 
 [dependencies]
 fxhash = "0.2.1"
+indexmap = "1.7.0"
 log = "0.4"
 once_cell = "1.5.2"
 pretty_assertions = {version = "0.6.1", optional = true}
@@ -31,10 +32,12 @@ swc_ecma_transforms = {version = "0.61.0", path = "../transforms/", features = [
 swc_ecma_transforms_base = {version = "0.24.0", path = "../transforms/base"}
 swc_ecma_utils = {version = "0.41.0", path = "../utils"}
 swc_ecma_visit = {version = "0.35.0", path = "../visit"}
+unicode-xid = "0.2.2"
 
 [dev-dependencies]
 ansi_term = "0.12.1"
 anyhow = "1"
 pretty_assertions = "0.6.1"
+swc_node_base = {version = "0.2.0", path = "../../node/base"}
 testing = {version = "0.12.0", path = "../../testing"}
 walkdir = "2.3.1"

ecmascript/minifier/README.md

@@ -8,6 +8,26 @@ Currently name mangler is very simple. To focus on creating a MVP, I (kdy1) will
 
 ## Testing
 
+### Real-library tests
+
+You can use vscode to see diffs. Select a file from `tests/projects/output` and select the corresponding file from `tests/projects/refs`. Then you can right click to see an option to open diff.
+
+#### Splitting a library test
+
+Extracting only subset from a library test makes development much easier.
+
+Split status:
+
+-   [ ] angular-1.2.5
+-   [x] backbone-1.1.0
+-   [ ] jquery-1.9.1
+-   [ ] jquery.mobile-1.4.2
+-   [ ] mootools-1.4.5
+-   [x] underscore-1.5.2
+-   [ ] yui-3.12.0
+
+### Tests from terser
+
 Tests ported from terser has
 
 -   input.js
@@ -16,6 +36,6 @@ Tests ported from terser has
 -   output.js (if exists and can be modified if our one is better or due to lack of frequency-aware base54)
 -   output.terser.js (if exists)
 
-## Copying tests
+#### Copying tests
 
 Replace the content of `terser/test/compress.js` with it of `scripts/compress.js` and run `npm run test:compress`

ecmascript/minifier/package.json

@@ -0,0 +1,20 @@
+{
+    "name": "minifier",
+    "private": true,
+    "version": "1.0.0",
+    "description": "EcmaScript minifier for the swc project. This is basically a port of terser.",
+    "main": "lab.js",
+    "directories": {
+        "test": "tests"
+    },
+    "scripts": {
+        "test": "echo \"Error: no test specified\" && exit 1"
+    },
+    "keywords": [],
+    "author": "",
+    "license": "ISC",
+    "devDependencies": {
+        "babel-eslint": "^10.1.0",
+        "eslint": "^7.29.0"
+    }
+}

ecmascript/minifier/scripts/add-golden.sh

@@ -6,10 +6,10 @@ set -eu
 
 export SWC_RUN=0
 
-cargo test --test compress --all-features \
+cargo test --test compress --all-features fixture_tests__terser__compress__ \
-  | grep 'terser__compress' \
+  | grep 'fixture_tests__terser__compress__' \
   | grep 'js .\.\. ok$' \
-  | sed -e 's!test fixture_terser__compress__!!' \
+  | sed -e 's!test fixture_tests__terser__compress__!!' \
   | sed -e 's! ... ok!!' \
   | sed -e 's!__!/!g' \
   | sed -e 's!_js!.js!' \

ecmascript/minifier/scripts/apply.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -eux
+
+
+# Prevent regression
+./scripts/run.sh
+
+export RUST_BACKTRACE=1
+export RUST_LOG=swc_ecma_minifier=trace
+touch tests/compress.rs
+
+UPDATE=1 cargo test --test compress files__projects --all-features || true
+
+# Make it easier to compare
+prettier --write tests/projects/output
+yarn run eslint --fix ./tests/projects/output/
+
+ls -al ./tests/projects/output
+ls -al ./tests/projects/refs

ecmascript/minifier/scripts/base.sh

@@ -5,4 +5,4 @@ export RUST_LOG=swc_ecma_minifier=trace
 
 # To prevent regression, we run base test before real tests.
 touch tests/compress.rs
-cargo test --test compress ${1-base_exec} --all-features
+cargo test --test compress ${1-base_exec} -q --all-features

ecmascript/minifier/scripts/ideal.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+# 
+# This scripts print the ideal output of lab.js
+#
+
+set -eux
+terser --compress --format beautify -- lab.js
+node lab.js

ecmascript/minifier/scripts/ignore.sh

@@ -3,10 +3,10 @@ set -eu
 
 export SWC_RUN=0
 
-cargo test --test compress --all-features ${1-''} \
+cargo test --test compress --all-features ${1-'fixture_tests__terser__compress__'} \
-  | grep 'terser__compress' \
+  | grep 'fixture_tests__terser__compress__' \
   | grep 'js .\.\. FAILED$' \
-  | sed -e 's!test fixture_terser__compress__!!' \
+  | sed -e 's!test fixture_tests__terser__compress__!!' \
   | sed -e 's! ... FAILED!!' \
   | sed -e 's!__!/!g' \
   | sed -e 's!_js!.js!' \

ecmascript/minifier/scripts/project-ref.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+set -eu
+
+run() {
+    terser --compress -- ./tests/projects/files/$1 > ./tests/projects/refs/$1
+}
+
+
+mkdir -p ./tests/projects/refs
+
+run angular-1.2.5.js
+run backbone-1.1.0.js
+run jquery-1.9.1.js
+run jquery.mobile-1.4.2.js
+run mootools-1.4.5.js
+run underscore-1.5.2.js
+run yui-3.12.0.js
+run react-17.0.2.js
+run react-dom-17.0.2.js
+
+prettier --write tests/projects/refs/
+yarn run eslint --fix ./tests/projects/refs/

ecmascript/minifier/scripts/run.sh

@@ -13,6 +13,9 @@ set -eu
 
 export RUST_LOG=swc_ecma_minifier=trace
 
+# Run unit tests.
+cargo test --all-features --lib
+
 # To prevent regression, we run base test before real tests.
 touch tests/compress.rs
 UPDATE=1 ./scripts/base.sh base_fixture
@@ -21,7 +24,7 @@ UPDATE=1 ./scripts/base.sh base_fixture
 if [ -z "$@" ]; then
     ./scripts/sort.sh
 
-    SWC_RUN=0 GOLDEN_ONLY=1 cargo test --test compress --all-features 
+    SWC_RUN=0 GOLDEN_ONLY=1 cargo test -q --test compress --all-features fixture_tests__terser__compress__
 fi
 
 SKIP_GOLDEN=1 cargo test --test compress --all-features $@

ecmascript/minifier/scripts/update-list.sh

@@ -12,4 +12,4 @@ set -eu
 echo '' > tests/ignored.txt
 
 scripts/add-golden.sh
-scripts/ignore.sh ''
+scripts/ignore.sh 'fixture_tests__terser__compress__'

ecmascript/minifier/src/analyzer/ctx.rs

@@ -17,6 +17,9 @@ impl UsageAnalyzer {
 #[derive(Debug, Default, Clone, Copy)]
 pub(super) struct Ctx {
     pub var_decl_kind_of_pat: Option<VarDeclKind>,
+
+    pub in_var_decl_with_no_side_effect_for_member_access: bool,
+
     pub in_pat_of_var_decl: bool,
     pub in_pat_of_var_decl_with_init: bool,
     pub in_pat_of_param: bool,
@@ -38,6 +41,8 @@ pub(super) struct Ctx {
     pub in_update_arg: bool,
     pub in_assign_lhs: bool,
     pub in_cond: bool,
+
+    pub inline_prevented: bool,
 }
 
 pub(super) struct WithCtx<'a> {

ecmascript/minifier/src/analyzer/mod.rs

@@ -4,6 +4,7 @@ use crate::util::idents_used_by;
 use fxhash::FxHashMap;
 use fxhash::FxHashSet;
 use std::collections::hash_map::Entry;
+use std::time::Instant;
 use swc_atoms::JsWord;
 use swc_common::SyntaxContext;
 use swc_common::DUMMY_SP;
@@ -24,6 +25,8 @@ pub(crate) fn analyze<N>(n: &N) -> ProgramData
 where
     N: VisitWith<UsageAnalyzer>,
 {
+    let start_time = Instant::now();
+
     let mut v = UsageAnalyzer {
         data: Default::default(),
         scope: Default::default(),
@@ -33,11 +36,17 @@ where
     let top_scope = v.scope;
     v.data.top.merge(top_scope, false);
 
+    let end_time = Instant::now();
+
+    log::debug!("Scope analysis took {:?}", end_time - start_time);
+
     v.data
 }
 
 #[derive(Debug, Default)]
 pub(crate) struct VarUsageInfo {
+    pub inline_prevented: bool,
+
     /// The number of reference to this identifier.
     pub ref_count: usize,
 
@@ -51,6 +60,8 @@ pub(crate) struct VarUsageInfo {
     /// `true` if the enclosing function defines this variable as a parameter.
     pub declared_as_fn_param: bool,
 
+    pub declared_as_fn_expr: bool,
+
     pub assign_count: usize,
     pub mutation_by_call_count: usize,
     pub usage_count: usize,
@@ -71,6 +82,8 @@ pub(crate) struct VarUsageInfo {
     /// functions.
     pub is_fn_local: bool,
 
+    used_by_nested_fn: bool,
+
     pub used_in_loop: bool,
 
     pub var_kind: Option<VarDeclKind>,
@@ -83,6 +96,8 @@ pub(crate) struct VarUsageInfo {
     /// Indicates a variable or function is overrided without using it.
     pub overriden_without_used: bool,
 
+    pub no_side_effect_for_member_access: bool,
+
     /// In `c = b`, `b` inffects `c`.
     infects: Vec<Id>,
 }
@@ -143,9 +158,12 @@ impl ProgramData {
             to.merge(scope, false);
         }
 
-        for (id, var_info) in child.vars {
+        for (id, mut var_info) in child.vars {
+            // log::trace!("merge({:?},{}{:?})", kind, id.0, id.1);
             match self.vars.entry(id) {
                 Entry::Occupied(mut e) => {
+                    e.get_mut().inline_prevented |= var_info.inline_prevented;
+
                     e.get_mut().ref_count += var_info.ref_count;
                     e.get_mut().cond_init |= var_info.cond_init;
 
@@ -158,6 +176,7 @@ impl ProgramData {
                     e.get_mut().declared |= var_info.declared;
                     e.get_mut().declared_count += var_info.declared_count;
                     e.get_mut().declared_as_fn_param |= var_info.declared_as_fn_param;
+                    e.get_mut().declared_as_fn_expr |= var_info.declared_as_fn_expr;
 
                     // If a var is registered at a parent scope, it means that it's delcared before
                     // usages.
@@ -172,14 +191,30 @@ impl ProgramData {
 
                     e.get_mut().infects.extend(var_info.infects);
 
+                    e.get_mut().no_side_effect_for_member_access =
+                        e.get_mut().no_side_effect_for_member_access
+                            && var_info.no_side_effect_for_member_access;
+
                     match kind {
                         ScopeKind::Fn => {
                             e.get_mut().is_fn_local = false;
+                            e.get_mut().used_by_nested_fn = true;
+                        }
+                        ScopeKind::Block => {
+                            if var_info.used_by_nested_fn {
+                                e.get_mut().is_fn_local = false;
+                                e.get_mut().used_by_nested_fn = true;
+                            }
                         }
-                        ScopeKind::Block => {}
                     }
                 }
                 Entry::Vacant(e) => {
+                    match kind {
+                        ScopeKind::Fn => {
+                            var_info.used_by_nested_fn = true;
+                        }
+                        ScopeKind::Block => {}
+                    }
                     e.insert(var_info);
                 }
             }
@@ -225,17 +260,25 @@ impl UsageAnalyzer {
     }
 
     fn report(&mut self, i: Id, is_modify: bool, dejavu: &mut FxHashSet<Id>) {
+        // log::trace!("report({}{:?})", i.0, i.1);
+
         let is_first = dejavu.is_empty();
 
         if !dejavu.insert(i.clone()) {
             return;
         }
 
-        let e = self.data.vars.entry(i).or_insert_with(|| VarUsageInfo {
+        let e = self.data.vars.entry(i.clone()).or_insert_with(|| {
-            used_above_decl: true,
+            // log::trace!("insert({}{:?})", i.0, i.1);
-            ..Default::default()
+
+            VarUsageInfo {
+                used_above_decl: true,
+                ..Default::default()
+            }
         });
 
+        e.inline_prevented |= self.ctx.inline_prevented;
+
         e.ref_count += 1;
         e.reassigned |= is_first && is_modify && self.ctx.is_exact_reassignment;
         // Passing object as a argument is possibly modification.
@@ -258,7 +301,7 @@ impl UsageAnalyzer {
     }
 
     fn report_usage(&mut self, i: &Ident, is_assign: bool) {
-        self.report(i.to_id(), is_assign, &mut Default::default())
+        self.report(i.to_id(), is_assign, &mut Default::default());
     }
 
     fn declare_decl(
@@ -266,7 +309,12 @@ impl UsageAnalyzer {
         i: &Ident,
         has_init: bool,
         kind: Option<VarDeclKind>,
+        is_fn_decl: bool,
     ) -> &mut VarUsageInfo {
+        // log::trace!("declare_decl({}{:?})", i.sym, i.span.ctxt);
+
+        let ctx = self.ctx;
+
         let v = self
             .data
             .vars
@@ -282,6 +330,9 @@ impl UsageAnalyzer {
                 is_fn_local: true,
                 var_kind: kind,
                 var_initialized: has_init,
+                no_side_effect_for_member_access: ctx
+                    .in_var_decl_with_no_side_effect_for_member_access,
+
                 ..Default::default()
             });
         self.scope
@@ -297,6 +348,8 @@ impl UsageAnalyzer {
         }
         v.declared_as_catch_param |= self.ctx.in_catch_param;
 
+        v.declared_as_fn_expr |= is_fn_decl;
+
         v
     }
 }
@@ -385,8 +438,22 @@ impl Visit for UsageAnalyzer {
         }
     }
 
+    fn visit_class(&mut self, n: &Class, _: &dyn Node) {
+        n.decorators.visit_with(n, self);
+
+        {
+            let ctx = Ctx {
+                inline_prevented: true,
+                ..self.ctx
+            };
+            n.super_class.visit_with(n, &mut *self.with_ctx(ctx));
+        }
+
+        n.body.visit_with(n, self);
+    }
+
     fn visit_class_decl(&mut self, n: &ClassDecl, _: &dyn Node) {
-        self.declare_decl(&n.ident, true, None);
+        self.declare_decl(&n.ident, true, None, false);
 
         n.visit_children_with(self);
     }
@@ -415,8 +482,20 @@ impl Visit for UsageAnalyzer {
         }
     }
 
+    fn visit_fn_expr(&mut self, n: &FnExpr, _: &dyn Node) {
+        n.visit_children_with(self);
+
+        if let Some(id) = &n.ident {
+            self.data
+                .vars
+                .entry(id.to_id())
+                .or_default()
+                .declared_as_fn_expr = true;
+        }
+    }
+
     fn visit_fn_decl(&mut self, n: &FnDecl, _: &dyn Node) {
-        self.declare_decl(&n.ident, true, None);
+        self.declare_decl(&n.ident, true, None, true);
 
         n.visit_children_with(self);
     }
@@ -432,12 +511,14 @@ impl Visit for UsageAnalyzer {
             };
             n.left.visit_with(n, &mut *child.with_ctx(ctx));
 
+            n.right.visit_with(n, child);
+
             let ctx = Ctx {
                 in_loop: true,
                 in_cond: true,
                 ..child.ctx
             };
-            n.body.visit_with(n, &mut *child.with_ctx(ctx))
+            n.body.visit_with(n, &mut *child.with_ctx(ctx));
         });
     }
 
@@ -597,6 +678,7 @@ impl Visit for UsageAnalyzer {
                         &i.id,
                         self.ctx.in_pat_of_var_decl_with_init,
                         self.ctx.var_decl_kind_of_pat,
+                        false,
                     );
 
                     if in_pat_of_param {
@@ -735,6 +817,10 @@ impl Visit for UsageAnalyzer {
         let ctx = Ctx {
             in_pat_of_var_decl: true,
             in_pat_of_var_decl_with_init: e.init.is_some(),
+            in_var_decl_with_no_side_effect_for_member_access: match e.init.as_deref() {
+                Some(Expr::Array(..) | Expr::Lit(..)) => true,
+                _ => false,
+            },
             ..self.ctx
         };
         e.name.visit_with(e, &mut *self.with_ctx(ctx));

ecmascript/minifier/src/compress/hoist_decls.rs

@@ -1,4 +1,3 @@
-use crate::analyzer::analyze;
 use crate::analyzer::ProgramData;
 use crate::analyzer::UsageAnalyzer;
 use crate::util::is_hoisted_var_decl_without_init;
@@ -24,21 +23,21 @@ pub(super) struct DeclHoisterConfig {
     pub top_level: bool,
 }
 
-pub(super) fn decl_hoister(config: DeclHoisterConfig) -> Hoister {
+pub(super) fn decl_hoister(config: DeclHoisterConfig, data: &ProgramData) -> Hoister {
     Hoister {
         config,
         changed: false,
-        data: None,
+        data,
     }
 }
 
-pub(super) struct Hoister {
+pub(super) struct Hoister<'a> {
     config: DeclHoisterConfig,
     changed: bool,
-    data: Option<ProgramData>,
+    data: &'a ProgramData,
 }
 
-impl Repeated for Hoister {
+impl Repeated for Hoister<'_> {
     fn changed(&self) -> bool {
         self.changed
     }
@@ -48,40 +47,30 @@ impl Repeated for Hoister {
     }
 }
 
-impl Hoister {
+impl Hoister<'_> {
     fn handle_stmt_likes<T>(&mut self, stmts: &mut Vec<T>)
     where
         T: StmtLike + IsModuleItem,
-        Vec<T>: VisitMutWith<Self> + VisitWith<UsageAnalyzer>,
+        Vec<T>: for<'aa> VisitMutWith<Hoister<'aa>> + VisitWith<UsageAnalyzer>,
     {
-        match self.data {
-            None => {
-                self.data = Some(analyze(stmts));
-            }
-            _ => {}
-        }
-
         stmts.visit_mut_children_with(self);
 
         let should_hoist = !is_sorted_by_key(stmts.iter(), |stmt| match stmt.as_stmt() {
             Some(stmt) => match stmt {
                 Stmt::Decl(Decl::Fn(..)) if self.config.hoist_fns => 1,
                 Stmt::Decl(Decl::Var(var)) if self.config.hoist_vars => {
-                    if let Some(data) = &self.data {
+                    let ids: Vec<Id> = find_ids(&var.decls);
-                        let ids: Vec<Id> = find_ids(&var.decls);
 
-                        if ids.iter().any(|id| {
+                    if ids.iter().any(|id| {
-                            data.vars
+                        self.data
-                                .get(id)
+                            .vars
-                                .map(|v| !v.used_above_decl)
+                            .get(id)
-                                .unwrap_or(false)
+                            .map(|v| !v.used_above_decl)
-                        }) {
+                            .unwrap_or(false)
-                            2
+                    }) {
-                        } else {
-                            3
-                        }
-                    } else {
                         2
+                    } else {
+                        3
                     }
                 }
                 _ => 3,
@@ -133,8 +122,8 @@ impl Hoister {
                                         if decl.init.is_none()
                                             && self
                                                 .data
-                                                .as_ref()
+                                                .vars
-                                                .and_then(|v| v.vars.get(&id.to_id()))
+                                                .get(&id.to_id())
                                                 .map(|v| v.declared_as_fn_param)
                                                 .unwrap_or(false)
                                         {
@@ -207,8 +196,8 @@ impl Hoister {
                                         if decl.init.is_none()
                                             && self
                                                 .data
-                                                .as_ref()
+                                                .vars
-                                                .and_then(|v| v.vars.get(&name.to_id()))
+                                                .get(&name.to_id())
                                                 .map(|v| v.declared_as_fn_param)
                                                 .unwrap_or(false)
                                         {
@@ -258,7 +247,7 @@ impl Hoister {
     }
 }
 
-impl VisitMut for Hoister {
+impl VisitMut for Hoister<'_> {
     noop_visit_mut_type!();
 
     fn visit_mut_stmts(&mut self, stmts: &mut Vec<Stmt>) {

ecmascript/minifier/src/compress/mod.rs

@@ -1,9 +1,12 @@
 use self::drop_console::drop_console;
 use self::hoist_decls::DeclHoisterConfig;
 use self::optimize::optimizer;
+use crate::analyzer::analyze;
+use crate::analyzer::ProgramData;
 use crate::compress::hoist_decls::decl_hoister;
 use crate::debug::dump;
 use crate::debug::invoke;
+use crate::marks::Marks;
 use crate::option::CompressOptions;
 use crate::util::Optional;
 #[cfg(feature = "pretty_assertions")]
@@ -13,12 +16,15 @@ use std::fmt;
 use std::fmt::Debug;
 use std::fmt::Display;
 use std::fmt::Formatter;
-use swc_common::chain;
+use std::time::Instant;
 use swc_common::comments::Comments;
 use swc_common::pass::CompilerPass;
 use swc_common::pass::Repeat;
 use swc_common::pass::Repeated;
+use swc_common::sync::Lrc;
+use swc_common::{chain, SourceMap};
 use swc_ecma_ast::*;
+use swc_ecma_transforms::fixer;
 use swc_ecma_transforms::optimization::simplify::dead_branch_remover;
 use swc_ecma_transforms::optimization::simplify::expr_simplifier;
 use swc_ecma_transforms::pass::JsPass;
@@ -34,7 +40,9 @@ mod drop_console;
 mod hoist_decls;
 mod optimize;
 
-pub fn compressor<'a>(
+pub(crate) fn compressor<'a>(
+    cm: Lrc<SourceMap>,
+    marks: Marks,
     options: &'a CompressOptions,
     comments: Option<&'a dyn Comments>,
 ) -> impl 'a + JsPass {
@@ -43,10 +51,13 @@ pub fn compressor<'a>(
         visitor: drop_console(),
     };
     let compressor = Compressor {
-        comments,
+        cm,
+        marks,
         options,
-        pass: 0,
+        comments,
         changed: false,
+        pass: 0,
+        data: None,
     };
 
     chain!(
@@ -57,10 +68,13 @@ pub fn compressor<'a>(
 }
 
 struct Compressor<'a> {
+    cm: Lrc<SourceMap>,
+    marks: Marks,
     options: &'a CompressOptions,
     comments: Option<&'a dyn Comments>,
     changed: bool,
     pass: usize,
+    data: Option<ProgramData>,
 }
 
 impl CompilerPass for Compressor<'_> {
@@ -77,6 +91,7 @@ impl Repeated for Compressor<'_> {
     fn reset(&mut self) {
         self.changed = false;
         self.pass += 1;
+        self.data = None;
     }
 }
 
@@ -84,7 +99,7 @@ impl Compressor<'_> {
     fn handle_stmt_likes<T>(&mut self, stmts: &mut Vec<T>)
     where
         T: StmtLike,
-        Vec<T>: VisitMutWith<Self> + VisitMutWith<hoist_decls::Hoister>,
+        Vec<T>: VisitMutWith<Self> + for<'aa> VisitMutWith<hoist_decls::Hoister<'aa>>,
     {
         // Skip if `use asm` exists.
         if stmts.iter().any(|stmt| match stmt.as_stmt() {
@@ -104,17 +119,6 @@ impl Compressor<'_> {
             return;
         }
 
-        {
-            let mut v = decl_hoister(DeclHoisterConfig {
-                hoist_fns: self.options.hoist_fns,
-                hoist_vars: self.options.hoist_vars,
-                top_level: self.options.top_level(),
-            });
-            stmts.visit_mut_with(&mut v);
-            self.changed |= v.changed();
-        }
-        // TODO: Hoist decls
-
         stmts.visit_mut_children_with(self);
 
         // TODO: drop unused
@@ -125,38 +129,56 @@ impl VisitMut for Compressor<'_> {
     noop_visit_mut_type!();
 
     fn visit_mut_module(&mut self, n: &mut Module) {
+        debug_assert!(self.data.is_none());
+        self.data = Some(analyze(&*n));
+
         if self.options.passes != 0 && self.options.passes + 1 <= self.pass {
             let done = dump(&*n);
-            log::trace!("===== Done =====\n{}", done);
+            log::debug!("===== Done =====\n{}", done);
             return;
         }
 
         // Temporary
-        if self.pass > 10 {
+        if self.pass > 30 {
-            panic!("Infinite loop detected")
+            panic!("Infinite loop detected (current pass = {})", self.pass)
         }
 
         let start = if cfg!(feature = "debug") {
-            let start = dump(&*n);
+            let start = dump(&n.clone().fold_with(&mut fixer(None)));
-            log::trace!("===== Start =====\n{}", start);
+            log::debug!("===== Start =====\n{}", start);
             start
         } else {
             String::new()
         };
 
         {
+            log::info!(
+                "compress: Running expression simplifier (pass = {})",
+                self.pass
+            );
+
+            let start_time = Instant::now();
+
             let mut visitor = expr_simplifier();
-            n.map_with_mut(|m| m.fold_with(&mut visitor));
+            n.visit_mut_with(&mut visitor);
             self.changed |= visitor.changed();
             if visitor.changed() {
-                log::trace!("compressor: Simplified expressions");
+                log::debug!("compressor: Simplified expressions");
                 if cfg!(feature = "debug") {
-                    log::trace!("===== Simplified =====\n{}", dump(&*n));
+                    log::debug!("===== Simplified =====\n{}", dump(&*n));
                 }
             }
 
+            let end_time = Instant::now();
+
+            log::info!(
+                "compress: expr_simplifier took {:?} (pass = {})",
+                end_time - start_time,
+                self.pass
+            );
+
             if cfg!(feature = "debug") && !visitor.changed() {
-                let simplified = dump(&*n);
+                let simplified = dump(&n.clone().fold_with(&mut fixer(None)));
                 if start != simplified {
                     assert_eq!(
                         DebugUsingDisplay(&start),
@@ -169,12 +191,31 @@ impl VisitMut for Compressor<'_> {
         }
 
         {
+            log::info!("compress: Running optimizer (pass = {})", self.pass);
+
+            let start_time = Instant::now();
             // TODO: reset_opt_flags
             //
             // This is swc version of `node.optimize(this);`.
-            let mut visitor = optimizer(self.options.clone(), self.comments);
+            let mut visitor = optimizer(
+                self.cm.clone(),
+                self.marks,
+                self.options,
+                self.comments,
+                self.data.as_ref().unwrap(),
+            );
             n.visit_mut_with(&mut visitor);
             self.changed |= visitor.changed();
+
+            let end_time = Instant::now();
+
+            log::info!(
+                "compress: Optimizer took {:?} (pass = {})",
+                end_time - start_time,
+                self.pass
+            );
+            // let done = dump(&*n);
+            // log::debug!("===== Result =====\n{}", done);
         }
 
         if self.options.conditionals || self.options.dead_code {
@@ -184,14 +225,18 @@ impl VisitMut for Compressor<'_> {
                 "".into()
             };
 
+            let start_time = Instant::now();
+
             let mut v = dead_branch_remover();
             n.map_with_mut(|n| n.fold_with(&mut v));
 
+            let end_time = Instant::now();
+
             if cfg!(feature = "debug") {
                 let simplified = dump(&*n);
 
                 if start != simplified {
-                    log::trace!(
+                    log::debug!(
                         "===== Removed dead branches =====\n{}\n==== ===== ===== ===== ======\n{}",
                         start,
                         simplified
@@ -199,6 +244,12 @@ impl VisitMut for Compressor<'_> {
                 }
             }
 
+            log::info!(
+                "compress: dead_branch_remover took {:?} (pass = {})",
+                end_time - start_time,
+                self.pass
+            );
+
             self.changed |= v.changed();
         }
 
@@ -207,14 +258,20 @@ impl VisitMut for Compressor<'_> {
         invoke(&*n);
     }
 
-    fn visit_mut_stmt(&mut self, n: &mut Stmt) {
-        // TODO: Skip if node is already optimized.
-        // if (has_flag(node, SQUEEZED)) return node;
-
-        n.visit_mut_children_with(self);
-    }
-
     fn visit_mut_module_items(&mut self, stmts: &mut Vec<ModuleItem>) {
+        {
+            let mut v = decl_hoister(
+                DeclHoisterConfig {
+                    hoist_fns: self.options.hoist_fns,
+                    hoist_vars: self.options.hoist_vars,
+                    top_level: self.options.top_level(),
+                },
+                self.data.as_ref().unwrap(),
+            );
+            stmts.visit_mut_with(&mut v);
+            self.changed |= v.changed();
+        }
+
         self.handle_stmt_likes(stmts);
 
         stmts.retain(|stmt| match stmt {
@@ -232,6 +289,26 @@ impl VisitMut for Compressor<'_> {
         });
     }
 
+    fn visit_mut_script(&mut self, n: &mut Script) {
+        debug_assert!(self.data.is_none());
+        self.data = Some(analyze(&*n));
+
+        {
+            let mut v = decl_hoister(
+                DeclHoisterConfig {
+                    hoist_fns: self.options.hoist_fns,
+                    hoist_vars: self.options.hoist_vars,
+                    top_level: self.options.top_level(),
+                },
+                self.data.as_ref().unwrap(),
+            );
+            n.body.visit_mut_with(&mut v);
+            self.changed |= v.changed();
+        }
+
+        n.visit_mut_children_with(self);
+    }
+
     fn visit_mut_stmts(&mut self, stmts: &mut Vec<Stmt>) {
         self.handle_stmt_likes(stmts);
 

ecmascript/minifier/src/compress/optimize/arguments.rs

@@ -1,12 +1,13 @@
 use super::Optimizer;
-use crate::analyzer::analyze;
 use crate::compress::optimize::is_left_access_to_arguments;
 use std::iter::repeat_with;
 use swc_atoms::js_word;
 use swc_common::DUMMY_SP;
 use swc_ecma_ast::*;
+use swc_ecma_utils::find_ids;
 use swc_ecma_utils::ident::IdentLike;
 use swc_ecma_utils::private_ident;
+use swc_ecma_utils::Id;
 use swc_ecma_visit::noop_visit_mut_type;
 use swc_ecma_visit::VisitMut;
 use swc_ecma_visit::VisitMutWith;
@@ -36,7 +37,7 @@ impl Optimizer<'_> {
                 }
 
                 self.changed = true;
-                log::trace!("arguments: Optimizing computed access to arguments");
+                log::debug!("arguments: Optimizing computed access to arguments");
                 member.computed = false;
                 member.prop = Box::new(Expr::Ident(Ident {
                     span: prop.span,
@@ -75,9 +76,9 @@ impl Optimizer<'_> {
 
         {
             // If a function has a variable named `arguments`, we abort.
-            let data = analyze(&f.body);
+            let data: Vec<Id> = find_ids(&f.body);
-            for (id, var) in &data.vars {
+            for id in &data {
-                if id.0 == js_word!("arguments") && var.declared {
+                if id.0 == js_word!("arguments") {
                     return;
                 }
             }
@@ -113,7 +114,7 @@ impl ArgReplacer<'_> {
         let new_args = idx + 1 - self.params.len();
 
         self.changed = true;
-        log::trace!("arguments: Injecting {} parameters", new_args);
+        log::debug!("arguments: Injecting {} parameters", new_args);
         let mut start = self.params.len();
         self.params.extend(
             repeat_with(|| {
@@ -191,7 +192,7 @@ impl VisitMut for ArgReplacer<'_> {
                                     if let Some(param) = self.params.get(idx) {
                                         match &param.pat {
                                             Pat::Ident(i) => {
-                                                log::trace!(
+                                                log::debug!(
                                                     "arguments: Replacing access to arguments to \
                                                      normal reference",
                                                 );

ecmascript/minifier/src/compress/optimize/arrows.rs

@@ -20,7 +20,7 @@ impl Optimizer<'_> {
                 if s.stmts.len() == 1 {
                     if let Stmt::Return(s) = &mut s.stmts[0] {
                         if let Some(arg) = &mut s.arg {
-                            log::trace!("arrows: Optimizing the body of an arrow");
+                            log::debug!("arrows: Optimizing the body of an arrow");
                             *b = BlockStmtOrExpr::Expr(arg.take());
                             return;
                         }

ecmascript/minifier/src/compress/optimize/bools.rs

@@ -1,71 +1,20 @@
 use super::Optimizer;
-use crate::compress::optimize::is_pure_undefined;
+use crate::compress::optimize::{is_pure_undefined, Ctx};
+use crate::debug::dump;
 use crate::util::make_bool;
 use swc_atoms::js_word;
 use swc_common::Spanned;
-use swc_common::DUMMY_SP;
 use swc_ecma_ast::*;
 use swc_ecma_transforms_base::ext::MapWithMut;
-use swc_ecma_utils::ExprExt;
+use swc_ecma_utils::ident::IdentLike;
 use swc_ecma_utils::Type;
 use swc_ecma_utils::Value;
 use swc_ecma_utils::Value::Known;
 use swc_ecma_utils::Value::Unknown;
+use swc_ecma_utils::{undefined, ExprExt};
 
 /// Methods related to the options `bools` and `bool_as_ints`.
 impl Optimizer<'_> {
-    /// Disabled because it can change semantics.
-    ///
-    /// - `!foo || bar();` => `foo && bar();`
-    /// - `!foo && bar();` => `foo || bar();`
-    pub(super) fn compress_logical_exprs_with_negated_lhs(&mut self, e: &mut Expr) {
-        if !self.options.bools || true {
-            return;
-        }
-
-        match e {
-            Expr::Bin(BinExpr {
-                span,
-                op: op @ op!("||"),
-                left,
-                right,
-                ..
-            })
-            | Expr::Bin(BinExpr {
-                span,
-                op: op @ op!("&&"),
-                left,
-                right,
-                ..
-            }) => match &mut **left {
-                Expr::Unary(UnaryExpr {
-                    op: op!("!"), arg, ..
-                }) => {
-                    if *op == op!("&&") {
-                        log::trace!("booleans: Compressing `!foo && bar` as `foo || bar`");
-                    } else {
-                        log::trace!("booleans: Compressing `!foo || bar` as `foo && bar`");
-                    }
-                    self.changed = true;
-                    *e = Expr::Bin(BinExpr {
-                        span: *span,
-                        left: arg.take(),
-                        op: if *op == op!("&&") {
-                            op!("||")
-                        } else {
-                            op!("&&")
-                        },
-                        right: right.take(),
-                    });
-                    return;
-                }
-                _ => {}
-            },
-
-            _ => {}
-        }
-    }
-
     ///
     /// - `!condition() || !-3.5` => `!condition()`
     ///
@@ -104,9 +53,9 @@ impl Optimizer<'_> {
 
                         if can_remove {
                             if *op == op!("&&") {
-                                log::trace!("booleans: Compressing `!foo && true` as `!foo`");
+                                log::debug!("booleans: Compressing `!foo && true` as `!foo`");
                             } else {
-                                log::trace!("booleans: Compressing `!foo || false` as `!foo`");
+                                log::debug!("booleans: Compressing `!foo || false` as `!foo`");
                             }
                             self.changed = true;
                             *e = *left.take();
@@ -128,10 +77,7 @@ impl Optimizer<'_> {
 
         match e {
             Expr::Unary(UnaryExpr {
-                span,
+                op: op!("!"), arg, ..
-                op: op!("!"),
-                arg,
-                ..
             }) => match &mut **arg {
                 Expr::Bin(BinExpr {
                     op: op!("&&"),
@@ -139,30 +85,123 @@ impl Optimizer<'_> {
                     right,
                     ..
                 }) => {
-                    log::trace!("Optimizing ``!(a && b)` as `!a || !b`");
+                    if negate_cost(&left, self.ctx.in_bool_ctx, false).unwrap_or(isize::MAX) >= 0
+                        || negate_cost(&right, self.ctx.in_bool_ctx, false).unwrap_or(isize::MAX)
+                            >= 0
+                    {
+                        return;
+                    }
+                    log::debug!("Optimizing `!(a && b)` as `!a || !b`");
                     self.changed = true;
-                    *e = Expr::Bin(BinExpr {
+                    self.negate(arg);
-                        span: *span,
+                    *e = *arg.take();
-                        op: op!("||"),
-                        left: Box::new(Expr::Unary(UnaryExpr {
-                            span: DUMMY_SP,
-                            op: op!("!"),
-                            arg: left.take(),
-                        })),
-                        right: Box::new(Expr::Unary(UnaryExpr {
-                            span: DUMMY_SP,
-                            op: op!("!"),
-                            arg: right.take(),
-                        })),
-                    });
                     return;
                 }
+
+                Expr::Unary(UnaryExpr {
+                    op: op!("!"),
+                    arg: arg_of_arg,
+                    ..
+                }) => match &mut **arg_of_arg {
+                    Expr::Bin(BinExpr {
+                        op: op!("||"),
+                        left,
+                        right,
+                        ..
+                    }) => {
+                        if negate_cost(&left, self.ctx.in_bool_ctx, false).unwrap_or(isize::MAX) > 0
+                            && negate_cost(&right, self.ctx.in_bool_ctx, false)
+                                .unwrap_or(isize::MAX)
+                                > 0
+                        {
+                            return;
+                        }
+                        log::debug!("Optimizing `!!(a || b)` as `!a && !b`");
+                        self.changed = true;
+                        self.negate(arg_of_arg);
+                        *e = *arg.take();
+                        return;
+                    }
+
+                    _ => {}
+                },
+
                 _ => {}
             },
             _ => {}
         }
     }
 
+    /// **This negates bool**.
+    ///
+    /// Returns true if it's negated.
+    pub(super) fn optimize_bang_within_logical_ops(
+        &mut self,
+        expr: &mut Expr,
+        is_ret_val_ignored: bool,
+    ) -> bool {
+        if negate_cost(&expr, is_ret_val_ignored, is_ret_val_ignored).unwrap_or(isize::MAX) >= 0 {
+            return false;
+        }
+
+        let e = match expr {
+            Expr::Bin(b) => b,
+            _ => return false,
+        };
+
+        match e.op {
+            op!("&&") | op!("||") => {}
+            _ => return false,
+        }
+
+        if !is_ret_val_ignored {
+            if let Known(Type::Bool) = e.left.get_type() {
+            } else {
+                // Don't change type.
+                return false;
+            }
+
+            if let Known(Type::Bool) = e.right.get_type() {
+            } else {
+                // Don't change type.
+                return false;
+            }
+        }
+
+        // `!_ && 'undefined' !== typeof require`
+        //
+        //  =>
+        //
+        // `_ || 'undefined' == typeof require`
+        log::debug!(
+            "bools({}): Negating: (!a && !b) => !(a || b) (because both expression are good for \
+             negation)",
+            self.line_col(e.span)
+        );
+        let start = dump(&*e);
+
+        e.op = if e.op == op!("&&") {
+            op!("||")
+        } else {
+            op!("&&")
+        };
+
+        let ctx = Ctx {
+            in_bool_ctx: true,
+            ..self.ctx
+        };
+
+        self.changed = true;
+        self.with_ctx(ctx).negate(&mut e.left);
+        self.with_ctx(ctx).negate(&mut e.right);
+
+        if cfg!(feature = "debug") {
+            log::trace!("[Change] {} => {}", start, dump(&*e));
+        }
+
+        true
+    }
+
     pub(super) fn compress_useless_deletes(&mut self, e: &mut Expr) {
         if !self.options.bools {
             return;
@@ -226,7 +265,7 @@ impl Optimizer<'_> {
                 } else {
                     self.changed = true;
                     let span = delete.arg.span();
-                    log::trace!("booleans: Compressing `delete` as sequence expression");
+                    log::debug!("booleans: Compressing `delete` as sequence expression");
                     *e = Expr::Seq(SeqExpr {
                         span,
                         exprs: vec![delete.arg.take(), Box::new(make_bool(span, true))],
@@ -241,26 +280,84 @@ impl Optimizer<'_> {
         if convert_to_true {
             self.changed = true;
             let span = delete.arg.span();
-            log::trace!("booleans: Compressing `delete` => true");
+            log::debug!("booleans: Compressing `delete` => true");
             *e = make_bool(span, true);
             return;
         }
     }
 
+    pub(super) fn compress_comparsion_of_typeof(&mut self, e: &mut BinExpr) {
+        fn should_optimize(l: &Expr, r: &Expr) -> bool {
+            match (l, r) {
+                (
+                    Expr::Unary(UnaryExpr {
+                        op: op!("typeof"), ..
+                    }),
+                    Expr::Lit(..),
+                ) => true,
+                _ => false,
+            }
+        }
+
+        match e.op {
+            op!("===") | op!("!==") => {}
+            _ => return,
+        }
+
+        if should_optimize(&e.left, &e.right) || should_optimize(&e.right, &e.left) {
+            log::debug!("bools: Compressing comparison of `typeof` with literal");
+            self.changed = true;
+            e.op = match e.op {
+                op!("===") => {
+                    op!("==")
+                }
+                op!("!==") => {
+                    op!("!=")
+                }
+                _ => {
+                    unreachable!()
+                }
+            }
+        }
+    }
+
     /// This method converts `!1` to `0`.
     pub(super) fn optimize_expr_in_bool_ctx(&mut self, n: &mut Expr) {
         if !self.options.bools {
             return;
         }
 
+        match n {
+            Expr::Bin(BinExpr {
+                op: op!("&&") | op!("||"),
+                left,
+                right,
+                ..
+            }) => {
+                // Regardless if it's truthy or falsy, we can optimize it because it will be
+                // casted as bool anyway.
+                self.optimize_expr_in_bool_ctx(&mut **left);
+                self.optimize_expr_in_bool_ctx(&mut **right);
+                return;
+            }
+
+            Expr::Seq(e) => {
+                if let Some(last) = e.exprs.last_mut() {
+                    self.optimize_expr_in_bool_ctx(&mut **last);
+                }
+            }
+
+            _ => {}
+        }
+
         match n {
             Expr::Unary(UnaryExpr {
                 span,
                 op: op!("!"),
                 arg,
-            }) => match &**arg {
+            }) => match &mut **arg {
                 Expr::Lit(Lit::Num(Number { value, .. })) => {
-                    log::trace!("Optimizing: number => number (in bool context)");
+                    log::debug!("Optimizing: number => number (in bool context)");
 
                     self.changed = true;
                     *n = Expr::Lit(Lit::Num(Number {
@@ -268,6 +365,15 @@ impl Optimizer<'_> {
                         value: if *value == 0.0 { 1.0 } else { 0.0 },
                     }))
                 }
+
+                Expr::Unary(UnaryExpr {
+                    op: op!("!"), arg, ..
+                }) => {
+                    log::debug!("bools: !!expr => expr (in bool ctx)");
+                    self.changed = true;
+                    *n = *arg.take();
+                    return;
+                }
                 _ => {}
             },
 
@@ -276,7 +382,7 @@ impl Optimizer<'_> {
                 op: op!("typeof"),
                 arg,
             }) => {
-                log::trace!("Optimizing: typeof => true (in bool context)");
+                log::debug!("Optimizing: typeof => true (in bool context)");
                 self.changed = true;
 
                 match &**arg {
@@ -301,7 +407,7 @@ impl Optimizer<'_> {
             }
 
             Expr::Lit(Lit::Str(s)) => {
-                log::trace!("Converting string as boolean expressions");
+                log::debug!("Converting string as boolean expressions");
                 self.changed = true;
                 *n = Expr::Lit(Lit::Num(Number {
                     span: s.span,
@@ -314,7 +420,7 @@ impl Optimizer<'_> {
                     return;
                 }
                 if self.options.bools {
-                    log::trace!("booleans: Converting number as boolean expressions");
+                    log::debug!("booleans: Converting number as boolean expressions");
                     self.changed = true;
                     *n = Expr::Lit(Lit::Num(Number {
                         span: num.span,
@@ -331,7 +437,7 @@ impl Optimizer<'_> {
             }) => {
                 // Optimize if (a ?? false); as if (a);
                 if let Value::Known(false) = right.as_pure_bool() {
-                    log::trace!(
+                    log::debug!(
                         "Dropping right operand of `??` as it's always false (in bool context)"
                     );
                     self.changed = true;
@@ -348,7 +454,7 @@ impl Optimizer<'_> {
                 // `a || false` => `a` (as it will be casted to boolean anyway)
 
                 if let Known(false) = right.as_pure_bool() {
-                    log::trace!("bools: `expr || false` => `expr` (in bool context)");
+                    log::debug!("bools: `expr || false` => `expr` (in bool context)");
                     self.changed = true;
                     *n = *left.take();
                     return;
@@ -359,8 +465,9 @@ impl Optimizer<'_> {
                 let span = n.span();
                 let v = n.as_pure_bool();
                 if let Known(v) = v {
-                    log::trace!("Optimizing expr as {} (in bool context)", v);
+                    log::debug!("Optimizing expr as {} (in bool context)", v);
                     *n = make_bool(span, v);
+                    return;
                 }
             }
         }
@@ -381,7 +488,7 @@ impl Optimizer<'_> {
             None => match &mut *stmt.cons {
                 Stmt::Expr(cons) => {
                     self.changed = true;
-                    log::trace!("conditionals: `if (foo) bar;` => `foo && bar`");
+                    log::debug!("conditionals: `if (foo) bar;` => `foo && bar`");
                     *s = Stmt::Expr(ExprStmt {
                         span: stmt.span,
                         expr: Box::new(Expr::Bin(BinExpr {
@@ -397,4 +504,286 @@ impl Optimizer<'_> {
             },
         }
     }
+
+    ///
+    /// - `"undefined" == typeof value;` => `void 0 === value`
+    pub(super) fn compress_typeof_undefined(&mut self, e: &mut BinExpr) {
+        fn opt(o: &mut Optimizer, l: &mut Expr, r: &mut Expr) -> bool {
+            match (&mut *l, &mut *r) {
+                (
+                    Expr::Lit(Lit::Str(Str {
+                        value: js_word!("undefined"),
+                        ..
+                    })),
+                    Expr::Unary(UnaryExpr {
+                        op: op!("typeof"),
+                        arg,
+                        ..
+                    }),
+                ) => {
+                    // TODO?
+                    match &**arg {
+                        Expr::Ident(arg) => {
+                            if let Some(usage) =
+                                o.data.as_ref().and_then(|data| data.vars.get(&arg.to_id()))
+                            {
+                                if !usage.declared {
+                                    return false;
+                                }
+                            }
+                        }
+                        _ => {}
+                    }
+
+                    *l = *undefined(l.span());
+                    *r = *arg.take();
+                    true
+                }
+                _ => false,
+            }
+        }
+
+        match e.op {
+            op!("==") | op!("!=") | op!("===") | op!("!==") => {}
+            _ => return,
+        }
+
+        if opt(self, &mut e.left, &mut e.right) || opt(self, &mut e.right, &mut e.left) {
+            e.op = match e.op {
+                op!("==") => {
+                    op!("===")
+                }
+                op!("!=") => {
+                    op!("!==")
+                }
+                _ => e.op,
+            };
+        }
+    }
+}
+
+pub(crate) fn is_ok_to_negate_for_cond(e: &Expr) -> bool {
+    match e {
+        Expr::Update(..) => false,
+        _ => true,
+    }
+}
+
+pub(crate) fn is_ok_to_negate_rhs(rhs: &Expr) -> bool {
+    match rhs {
+        Expr::Member(..) => true,
+        Expr::Bin(BinExpr {
+            op: op!("===") | op!("!==") | op!("==") | op!("!="),
+            ..
+        }) => true,
+
+        Expr::Call(..) | Expr::New(..) => false,
+
+        Expr::Update(..) => false,
+
+        Expr::Bin(BinExpr {
+            op: op!("&&") | op!("||"),
+            left,
+            right,
+            ..
+        }) => is_ok_to_negate_rhs(&left) && is_ok_to_negate_rhs(&right),
+
+        Expr::Bin(BinExpr { left, right, .. }) => {
+            is_ok_to_negate_rhs(&left) && is_ok_to_negate_rhs(&right)
+        }
+
+        Expr::Assign(e) => is_ok_to_negate_rhs(&e.right),
+
+        Expr::Unary(UnaryExpr {
+            op: op!("!") | op!("delete"),
+            ..
+        }) => true,
+
+        Expr::Seq(e) => {
+            if let Some(last) = e.exprs.last() {
+                is_ok_to_negate_rhs(&last)
+            } else {
+                true
+            }
+        }
+
+        Expr::Cond(e) => is_ok_to_negate_rhs(&e.cons) && is_ok_to_negate_rhs(&e.alt),
+
+        _ => {
+            if !rhs.may_have_side_effects() {
+                return true;
+            }
+
+            if cfg!(feature = "debug") {
+                log::warn!("unimplemented: is_ok_to_negate_rhs: `{}`", dump(&*rhs));
+            }
+
+            false
+        }
+    }
+}
+
+/// A negative value means that it's efficient to negate the expression.
+pub(crate) fn negate_cost(e: &Expr, in_bool_ctx: bool, is_ret_val_ignored: bool) -> Option<isize> {
+    fn cost(
+        e: &Expr,
+        in_bool_ctx: bool,
+        bin_op: Option<BinaryOp>,
+        is_ret_val_ignored: bool,
+    ) -> isize {
+        match e {
+            Expr::Unary(UnaryExpr {
+                op: op!("!"), arg, ..
+            }) => {
+                // TODO: Check if this argument is actually start of line.
+                match &**arg {
+                    Expr::Call(CallExpr {
+                        callee: ExprOrSuper::Expr(callee),
+                        ..
+                    }) => match &**callee {
+                        Expr::Fn(..) => return 0,
+                        _ => {}
+                    },
+                    _ => {}
+                }
+
+                if in_bool_ctx {
+                    let c = -cost(arg, true, None, is_ret_val_ignored);
+                    return c.min(-1);
+                }
+
+                match &**arg {
+                    Expr::Unary(UnaryExpr { op: op!("!"), .. }) => -1,
+
+                    _ => 1,
+                }
+            }
+            Expr::Bin(BinExpr {
+                op: op!("===") | op!("!==") | op!("==") | op!("!="),
+                ..
+            }) => 0,
+
+            Expr::Bin(BinExpr {
+                op: op @ op!("||") | op @ op!("&&"),
+                left,
+                right,
+                ..
+            }) => {
+                let l_cost = cost(&left, in_bool_ctx, Some(*op), false);
+
+                if !is_ret_val_ignored && !is_ok_to_negate_rhs(&right) {
+                    return l_cost + 3;
+                }
+                l_cost + cost(&right, in_bool_ctx, Some(*op), is_ret_val_ignored)
+            }
+
+            Expr::Cond(CondExpr { cons, alt, .. })
+                if is_ok_to_negate_for_cond(&cons) && is_ok_to_negate_for_cond(&alt) =>
+            {
+                cost(&cons, in_bool_ctx, bin_op, is_ret_val_ignored)
+                    + cost(&alt, in_bool_ctx, bin_op, is_ret_val_ignored)
+            }
+
+            Expr::Cond(..)
+            | Expr::Update(..)
+            | Expr::Bin(BinExpr {
+                op: op!("in") | op!("instanceof"),
+                ..
+            }) => 3,
+
+            Expr::Assign(..) => {
+                if is_ret_val_ignored {
+                    0
+                } else {
+                    3
+                }
+            }
+
+            Expr::Seq(e) => {
+                if let Some(last) = e.exprs.last() {
+                    return cost(&last, in_bool_ctx, bin_op, is_ret_val_ignored);
+                }
+
+                if is_ret_val_ignored {
+                    0
+                } else {
+                    1
+                }
+            }
+
+            _ => {
+                if is_ret_val_ignored {
+                    0
+                } else {
+                    1
+                }
+            }
+        }
+    }
+
+    let cost = cost(e, in_bool_ctx, None, is_ret_val_ignored);
+
+    if cfg!(feature = "debug") {
+        log::trace!("negation cost of `{}` = {}", dump(&*e), cost);
+    }
+
+    Some(cost)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::negate_cost;
+    use swc_common::{input::SourceFileInput, FileName};
+    use swc_ecma_parser::{lexer::Lexer, Parser};
+
+    fn assert_negate_cost(s: &str, in_bool_ctx: bool, is_ret_val_ignored: bool, expected: isize) {
+        testing::run_test2(false, |cm, _| {
+            let fm = cm.new_source_file(FileName::Anon, s.to_string());
+
+            let lexer = Lexer::new(
+                Default::default(),
+                swc_ecma_ast::EsVersion::latest(),
+                SourceFileInput::from(&*fm),
+                None,
+            );
+
+            let mut parser = Parser::new_from(lexer);
+
+            let e = parser
+                .parse_expr()
+                .expect("failed to parse input as an expression");
+
+            let actual = negate_cost(&e, in_bool_ctx, is_ret_val_ignored).unwrap();
+
+            assert_eq!(
+                actual, expected,
+                "Expected negation cost of {} to be {}, but got {}",
+                s, expected, actual,
+            );
+
+            Ok(())
+        })
+        .unwrap();
+    }
+
+    #[test]
+    fn logical_1() {
+        assert_negate_cost(
+            "this[key] && !this.hasOwnProperty(key) || (this[key] = value)",
+            false,
+            true,
+            2,
+        );
+    }
+
+    #[test]
+    #[ignore]
+    fn logical_2() {
+        assert_negate_cost(
+            "(!this[key] || this.hasOwnProperty(key)) && (this[key] = value)",
+            false,
+            true,
+            -2,
+        );
+    }
 }

ecmascript/minifier/src/compress/optimize/collapse_vars.rs

@@ -4,6 +4,7 @@ use swc_common::DUMMY_SP;
 use swc_ecma_ast::*;
 use swc_ecma_transforms_base::ext::MapWithMut;
 use swc_ecma_utils::ident::IdentLike;
+use swc_ecma_utils::prepend;
 use swc_ecma_utils::Id;
 use swc_ecma_utils::StmtLike;
 use swc_ecma_visit::noop_visit_mut_type;
@@ -57,7 +58,7 @@ impl Optimizer<'_> {
             return;
         }
 
-        if self.ctx.in_try_block || self.ctx.executed_multiple_time {
+        if self.ctx.in_try_block || self.ctx.executed_multiple_time || self.ctx.in_cond {
             return;
         }
 
@@ -84,6 +85,20 @@ impl Optimizer<'_> {
                     {
                         return;
                     }
+
+                    if usage.used_in_loop {
+                        match &*assign.right {
+                            Expr::Lit(..) | Expr::Ident(..) => {}
+                            _ => return,
+                        }
+                    }
+
+                    if usage.usage_count >= 2 {
+                        match &*assign.right {
+                            Expr::Lit(..) => {}
+                            _ => return,
+                        }
+                    }
                 }
 
                 let value = match &*assign.right {
@@ -94,6 +109,12 @@ impl Optimizer<'_> {
                     _ => return,
                 };
 
+                log::debug!(
+                    "collpase_vars: Decided to inline {}{:?}",
+                    left.id.sym,
+                    left.id.span.ctxt
+                );
+
                 self.lits.insert(left.to_id(), value);
             }
             _ => {}
@@ -101,139 +122,284 @@ impl Optimizer<'_> {
     }
 
     /// Collapse single-use non-constant variables, side effects permitting.
-    pub(super) fn collapse_consequtive_vars<T>(&mut self, stmts: &mut Vec<T>)
+    ///
+    /// This merges all variables to first variable declartion with an
+    /// initializer. If such variable declaration is not found, variables are
+    /// prepended to `stmts`.
+    pub(super) fn collapse_vars_without_init<T>(&mut self, stmts: &mut Vec<T>)
     where
         T: StmtLike,
+        Vec<T>:
+            VisitWith<VarWithOutInitCounter> + VisitMutWith<VarMover> + VisitMutWith<VarPrepender>,
     {
         if !self.options.collapse_vars {
             return;
         }
 
-        let indexes = stmts
+        {
-            .windows(2)
+            // let mut found_other = false;
-            .enumerate()
+            // let mut need_work = false;
-            .filter_map(|(i, stmts)| {
-                match (stmts[0].as_stmt(), stmts[1].as_stmt()) {
-                    (Some(Stmt::Decl(Decl::Var(v))), Some(r)) => {
-                        // Should be handled by other passes.
-                        if v.kind == VarDeclKind::Const {
-                            return None;
-                        }
 
-                        // We only inline for some subset of statements.
+            // for stmt in &*stmts {
-                        match r {
+            //     match stmt.as_stmt() {
-                            Stmt::Expr(..) | Stmt::Return(..) => {}
+            //         Some(Stmt::Decl(Decl::Var(
-                            _ => return None,
+            //             v
-                        }
+            //             @
+            //             VarDecl {
+            //                 kind: VarDeclKind::Var,
+            //                 ..
+            //             },
+            //         ))) => {
+            //             if v.decls.iter().any(|v| v.init.is_none()) {
+            //                 if found_other {
+            //                     need_work = true;
+            //                 }
+            //             } else {
+            //                 found_other = true;
+            //             }
+            //         }
 
-                        // We only touch last variable delcarator.
+            //         _ => {
-                        if let Some(last) = v.decls.last() {
+            //             found_other = true;
-                            match last.init.as_deref()? {
+            //         }
-                                Expr::Object(..) => {
+            //     }
-                                    // Objects are handled by other passes.
+            // }
-                                    return None;
-                                }
-                                Expr::Arrow(..) | Expr::Fn(..) => {
-                                    // Handled by other passes
-                                    return None;
-                                }
 
-                                _ => {
+            // Check for nested variable declartions.
-                                    let mut chekcer = InlinabiltyChecker { can_inline: true };
+            let mut v = VarWithOutInitCounter::default();
-                                    last.init
+            stmts.visit_with(&Invalid { span: DUMMY_SP }, &mut v);
-                                        .visit_with(&Invalid { span: DUMMY_SP }, &mut chekcer);
+            if !v.need_work {
-                                    if !chekcer.can_inline {
+                return;
-                                        return None;
+            }
-                                    }
-                                }
-                            }
-
-                            match &last.name {
-                                Pat::Ident(name) => {
-                                    //
-                                    if let Some(var) = self
-                                        .data
-                                        .as_ref()
-                                        .and_then(|data| data.vars.get(&name.to_id()))
-                                    {
-                                        if var.usage_count != 1
-                                            || var.mutated
-                                            || !SimpleUsageFinder::find(&name.id, r)
-                                        {
-                                            return None;
-                                        }
-
-                                        return Some(i);
-                                    }
-
-                                    None
-                                }
-                                _ => None,
-                            }
-                        } else {
-                            None
-                        }
-                    }
-                    _ => None,
-                }
-            })
-            .collect::<Vec<_>>();
-
-        if indexes.is_empty() {
-            return;
         }
 
         self.changed = true;
-        log::trace!("collapse_vars: Collapsing {:?}", indexes);
+        log::debug!("collapse_vars: Collapsing variables without an initializer");
 
-        let mut new = Vec::with_capacity(stmts.len());
+        let vars = {
-        let mut values = FxHashMap::default();
+            let mut v = VarMover {
-        for (idx, stmt) in stmts.take().into_iter().enumerate() {
+                vars: Default::default(),
-            match stmt.try_into_stmt() {
+                var_decl_kind: Default::default(),
-                Ok(mut stmt) => match stmt {
+            };
-                    Stmt::Decl(Decl::Var(mut v)) if indexes.contains(&idx) => {
+            stmts.visit_mut_with(&mut v);
-                        if let Some(last) = v.decls.pop() {
-                            match last.name {
-                                Pat::Ident(name) => {
-                                    values.insert(name.to_id(), last.init);
-                                }
-                                _ => unreachable!(),
-                            }
-                        } else {
-                            unreachable!()
-                        }
-                    }
-                    _ => {
-                        stmt.visit_mut_with(&mut Inliner {
-                            values: &mut values,
-                        });
 
-                        new.push(T::from_stmt(stmt));
+            v.vars
-                    }
+        };
-                },
+
-                Err(item) => {
+        // Prepend vars
-                    new.push(item);
+
+        let mut prepender = VarPrepender { vars };
+        stmts.visit_mut_with(&mut prepender);
+
+        if !prepender.vars.is_empty() {
+            prepend(
+                stmts,
+                T::from_stmt(Stmt::Decl(Decl::Var(VarDecl {
+                    span: DUMMY_SP,
+                    kind: VarDeclKind::Var,
+                    declare: Default::default(),
+                    decls: prepender.vars,
+                }))),
+            );
+        }
+    }
+}
+
+/// See if there's two [VarDecl] which has [VarDeclarator] without the
+/// initializer.
+#[derive(Default)]
+pub(super) struct VarWithOutInitCounter {
+    need_work: bool,
+    found_var_without_init: bool,
+    found_var_with_init: bool,
+}
+
+impl Visit for VarWithOutInitCounter {
+    noop_visit_type!();
+
+    fn visit_arrow_expr(&mut self, _: &ArrowExpr, _: &dyn Node) {}
+
+    fn visit_constructor(&mut self, _: &Constructor, _: &dyn Node) {}
+
+    fn visit_function(&mut self, _: &Function, _: &dyn Node) {}
+
+    fn visit_var_decl(&mut self, v: &VarDecl, _: &dyn Node) {
+        v.visit_children_with(self);
+
+        if v.kind != VarDeclKind::Var {
+            return;
+        }
+
+        let mut found_init = false;
+        for d in &v.decls {
+            if d.init.is_some() {
+                found_init = true;
+            } else {
+                if found_init {
+                    self.need_work = true;
+                    return;
                 }
             }
         }
 
-        *stmts = new;
+        if v.decls.iter().all(|v| v.init.is_none()) {
+            if self.found_var_without_init || self.found_var_with_init {
+                self.need_work = true;
+            }
+            self.found_var_without_init = true;
+        } else {
+            self.found_var_with_init = true;
+        }
+    }
 
-        //
+    fn visit_var_decl_or_pat(&mut self, _: &VarDeclOrPat, _: &dyn Node) {}
+}
+
+/// Moves all varaible without initializer.
+pub(super) struct VarMover {
+    vars: Vec<VarDeclarator>,
+    var_decl_kind: Option<VarDeclKind>,
+}
+
+impl VisitMut for VarMover {
+    noop_visit_mut_type!();
+
+    /// Noop
+    fn visit_mut_arrow_expr(&mut self, _: &mut ArrowExpr) {}
+
+    /// Noop
+    fn visit_mut_constructor(&mut self, _: &mut Constructor) {}
+
+    /// Noop
+    fn visit_mut_function(&mut self, _: &mut Function) {}
+
+    fn visit_mut_module_item(&mut self, s: &mut ModuleItem) {
+        s.visit_mut_children_with(self);
+
+        match s {
+            ModuleItem::ModuleDecl(ModuleDecl::ExportDecl(ExportDecl {
+                decl: Decl::Var(d),
+                ..
+            })) if d.decls.is_empty() => {
+                s.take();
+                return;
+            }
+
+            _ => {}
+        }
+    }
+
+    fn visit_mut_opt_var_decl_or_expr(&mut self, n: &mut Option<VarDeclOrExpr>) {
+        n.visit_mut_children_with(self);
+
+        match n {
+            Some(VarDeclOrExpr::VarDecl(var)) => {
+                if var.decls.is_empty() {
+                    *n = None;
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn visit_mut_stmt(&mut self, s: &mut Stmt) {
+        s.visit_mut_children_with(self);
+
+        match s {
+            Stmt::Decl(Decl::Var(v)) if v.decls.is_empty() => {
+                s.take();
+                return;
+            }
+            _ => {}
+        }
+    }
+
+    fn visit_mut_var_decl(&mut self, v: &mut VarDecl) {
+        let old = self.var_decl_kind.take();
+        self.var_decl_kind = Some(v.kind);
+        v.visit_mut_children_with(self);
+        self.var_decl_kind = old;
+    }
+
+    fn visit_mut_var_decl_or_pat(&mut self, _: &mut VarDeclOrPat) {}
+
+    fn visit_mut_var_declarators(&mut self, d: &mut Vec<VarDeclarator>) {
+        d.visit_mut_children_with(self);
+
+        if self.var_decl_kind.unwrap() != VarDeclKind::Var {
+            return;
+        }
+
+        if d.iter().all(|v| v.init.is_some()) {
+            return;
+        }
+
+        let has_init = d.iter().any(|v| v.init.is_some());
+
+        if has_init {
+            let mut new = vec![];
+
+            for v in d.take() {
+                if v.init.is_some() {
+                    new.push(v)
+                } else {
+                    self.vars.push(v)
+                }
+            }
+
+            *d = new;
+        }
+
+        let mut new = vec![];
+
+        if has_init {
+            new.extend(self.vars.drain(..));
+        }
+
+        for v in d.take() {
+            if v.init.is_some() {
+                new.push(v)
+            } else {
+                self.vars.push(v)
+            }
+        }
+
+        *d = new;
     }
 }
 
-/// Checks inlinabilty of variable initializer.
+pub(super) struct VarPrepender {
-struct InlinabiltyChecker {
+    vars: Vec<VarDeclarator>,
-    can_inline: bool,
 }
 
-impl Visit for InlinabiltyChecker {
+impl VisitMut for VarPrepender {
-    noop_visit_type!();
+    noop_visit_mut_type!();
 
-    fn visit_update_expr(&mut self, _: &UpdateExpr, _: &dyn Node) {
+    fn visit_mut_var_decl(&mut self, v: &mut VarDecl) {
-        self.can_inline = false;
+        if self.vars.is_empty() {
+            return;
+        }
+
+        if v.kind != VarDeclKind::Var {
+            return;
+        }
+
+        if v.decls.iter().any(|d| d.init.is_some()) {
+            let mut decls = self.vars.take();
+            decls.extend(v.decls.take());
+
+            v.decls = decls;
+        }
     }
+
+    /// Noop
+    fn visit_mut_function(&mut self, _: &mut Function) {}
+
+    /// Noop
+    fn visit_mut_arrow_expr(&mut self, _: &mut ArrowExpr) {}
+
+    /// Noop
+    fn visit_mut_constructor(&mut self, _: &mut Constructor) {}
 }
 
 struct Inliner<'a> {
@@ -249,6 +415,8 @@ impl VisitMut for Inliner<'_> {
         match e {
             Expr::Ident(i) => {
                 if let Some(value) = self.values.remove(&i.to_id()) {
+                    log::debug!("collapse_vars: Inlining {}{:?}", i.sym, i.span.ctxt);
+
                     *e = *value.expect("should be used only once");
                 }
             }
@@ -256,63 +424,3 @@ impl VisitMut for Inliner<'_> {
         }
     }
 }
-
-/// Finds usage of `ident`, but except assignment to it.
-struct SimpleUsageFinder<'a> {
-    ident: &'a Ident,
-    found: bool,
-}
-
-impl<'a> Visit for SimpleUsageFinder<'a> {
-    noop_visit_type!();
-
-    fn visit_pat(&mut self, n: &Pat, _: &dyn Node) {
-        match n {
-            Pat::Ident(..) => {}
-            _ => {
-                n.visit_children_with(self);
-            }
-        }
-    }
-
-    fn visit_update_expr(&mut self, _: &UpdateExpr, _: &dyn Node) {}
-
-    fn visit_expr_or_spread(&mut self, n: &ExprOrSpread, _: &dyn Node) {
-        if n.spread.is_some() {
-            return;
-        }
-        n.visit_children_with(self);
-    }
-
-    fn visit_assign_expr(&mut self, e: &AssignExpr, _: &dyn Node) {
-        e.right.visit_with(e, self);
-    }
-
-    fn visit_ident(&mut self, i: &Ident, _: &dyn Node) {
-        if i.span.ctxt() == self.ident.span.ctxt() && i.sym == self.ident.sym {
-            self.found = true;
-        }
-    }
-
-    fn visit_member_expr(&mut self, e: &MemberExpr, _: &dyn Node) {
-        e.obj.visit_with(e as _, self);
-
-        if e.computed {
-            e.prop.visit_with(e as _, self);
-        }
-    }
-}
-
-impl<'a> SimpleUsageFinder<'a> {
-    pub fn find<N>(ident: &'a Ident, node: &N) -> bool
-    where
-        N: VisitWith<Self>,
-    {
-        let mut v = SimpleUsageFinder {
-            ident,
-            found: false,
-        };
-        node.visit_with(&Invalid { span: DUMMY_SP } as _, &mut v);
-        v.found
-    }
-}

ecmascript/minifier/src/compress/optimize/conditionals.rs

@@ -1,6 +1,11 @@
 use super::Optimizer;
+use crate::compress::optimize::bools::negate_cost;
+use crate::compress::optimize::Ctx;
+use crate::compress::optimize::DISABLE_BUGGY_PASSES;
+use crate::debug::dump;
 use crate::util::make_bool;
 use crate::util::SpanExt;
+use std::mem::swap;
 use swc_common::EqIgnoreSpan;
 use swc_common::Spanned;
 use swc_common::DUMMY_SP;
@@ -18,6 +23,104 @@ use swc_ecma_utils::Value::Known;
 /// Methods related to the option `conditionals`. All methods are noop if
 /// `conditionals` is false.
 impl Optimizer<'_> {
+    pub(super) fn negate_cond_expr(&mut self, cond: &mut CondExpr) {
+        if negate_cost(&cond.test, true, false).unwrap_or(isize::MAX) >= 0 {
+            return;
+        }
+
+        self.changed = true;
+        log::debug!("conditionals: `a ? foo : bar` => `!a ? bar : foo` (considered cost)");
+        let start_str = dump(&*cond);
+
+        {
+            let ctx = Ctx {
+                in_bool_ctx: true,
+                ..self.ctx
+            };
+            self.with_ctx(ctx).negate(&mut cond.test);
+        }
+        swap(&mut cond.cons, &mut cond.alt);
+
+        if cfg!(feature = "debug") {
+            log::trace!(
+                "[Change] Negated cond: `{}` => `{}`",
+                start_str,
+                dump(&*cond)
+            )
+        }
+    }
+
+    /// Negates the condition of a `if` statement to reduce body size.
+    pub(super) fn negate_if_stmt(&mut self, stmt: &mut IfStmt) {
+        let alt = match stmt.alt.as_deref_mut() {
+            Some(v) => v,
+            _ => return,
+        };
+
+        match &*stmt.cons {
+            Stmt::Return(..) | Stmt::Continue(ContinueStmt { label: None, .. }) => return,
+            _ => {}
+        }
+
+        if negate_cost(&stmt.test, true, false).unwrap_or(isize::MAX) < 0 {
+            self.changed = true;
+            log::debug!("if_return: Negating `cond` of an if statement which has cons and alt");
+            let ctx = Ctx {
+                in_bool_ctx: true,
+                ..self.ctx
+            };
+            self.with_ctx(ctx).negate(&mut stmt.test);
+            swap(alt, &mut *stmt.cons);
+            return;
+        }
+
+        match &*alt {
+            Stmt::Return(..) | Stmt::Continue(ContinueStmt { label: None, .. }) => {
+                self.changed = true;
+                log::debug!(
+                    "if_return: Negating an if statement because the alt is return / continue"
+                );
+                self.negate(&mut stmt.test);
+                swap(alt, &mut *stmt.cons);
+            }
+            _ => return,
+        }
+    }
+
+    /// This method may change return value.
+    ///
+    /// - `a ? b : false` => `a && b`
+    pub(super) fn compress_cond_to_logical_ignoring_return_value(&mut self, e: &mut Expr) {
+        let cond = match e {
+            Expr::Cond(cond) => cond,
+            _ => return,
+        };
+
+        if !cond.cons.may_have_side_effects() {
+            self.changed = true;
+            log::debug!("conditionals: `cond ? useless : alt` => `cond || alt`");
+            *e = Expr::Bin(BinExpr {
+                span: cond.span,
+                op: op!("||"),
+                left: cond.test.take(),
+                right: cond.alt.take(),
+            });
+            return;
+        }
+
+        if !cond.alt.may_have_side_effects() {
+            self.changed = true;
+            log::debug!("conditionals: `cond ? cons : useless` => `cond && cons`");
+            *e = Expr::Bin(BinExpr {
+                span: cond.span,
+                op: op!("&&"),
+                left: cond.test.take(),
+                right: cond.cons.take(),
+            });
+            return;
+        }
+    }
+
     /// Removes useless operands of an logical expressions.
     pub(super) fn drop_logical_operands(&mut self, e: &mut Expr) {
         if !self.options.conditionals {
@@ -47,7 +150,7 @@ impl Optimizer<'_> {
             // `!!b || true` => true
             if let Known(true) = rb {
                 self.changed = true;
-                log::trace!("conditionals: `!!foo || true` => `true`");
+                log::debug!("conditionals: `!!foo || true` => `true`");
                 *e = make_bool(bin.span, true);
                 return;
             }
@@ -70,7 +173,7 @@ impl Optimizer<'_> {
             (Expr::Bin(cons @ BinExpr { op: op!("||"), .. }), alt)
                 if (*cons.right).eq_ignore_span(&*alt) =>
             {
-                log::trace!("conditionals: `x ? y || z : z` => `x || y && z`");
+                log::debug!("conditionals: `x ? y || z : z` => `x || y && z`");
                 self.changed = true;
 
                 *e = Expr::Bin(BinExpr {
@@ -91,13 +194,10 @@ impl Optimizer<'_> {
     }
 
     ///
-    /// - `foo ? 1 : false` => `!!foo && 1`
+    /// - `foo ? bar : false` => `!!foo && bar`
-    /// - `!foo ? true : 0` => `!foo || 0`
+    /// - `!foo ? true : bar` => `!foo || bar`
+    /// - `foo ? false : bar` => `!foo && bar`
     pub(super) fn compress_conds_as_logical(&mut self, e: &mut Expr) {
-        if !self.options.conditionals {
-            return;
-        }
-
         let cond = match e {
             Expr::Cond(cond) => cond,
             _ => return,
@@ -107,7 +207,7 @@ impl Optimizer<'_> {
         if let Known(Type::Bool) = lt {
             let lb = cond.cons.as_pure_bool();
             if let Known(true) = lb {
-                log::trace!("conditionals: `foo ? true : bar` => `!!foo || bar`");
+                log::debug!("conditionals: `foo ? true : bar` => `!!foo || bar`");
 
                 // Negate twice to convert `test` to boolean.
                 self.negate_twice(&mut cond.test);
@@ -123,21 +223,19 @@ impl Optimizer<'_> {
             }
 
             // TODO: Verify this rule.
-            if false {
+            if let Known(false) = lb {
-                if let Known(false) = lb {
+                log::debug!("conditionals: `foo ? false : bar` => `!foo && bar`");
-                    log::trace!("conditionals: `foo ? false : bar` => `!foo && bar`");
 
-                    self.changed = true;
+                self.changed = true;
-                    self.negate(&mut cond.test);
+                self.negate(&mut cond.test);
 
-                    *e = Expr::Bin(BinExpr {
+                *e = Expr::Bin(BinExpr {
-                        span: cond.span,
+                    span: cond.span,
-                        op: op!("&&"),
+                    op: op!("&&"),
-                        left: cond.test.take(),
+                    left: cond.test.take(),
-                        right: cond.alt.take(),
+                    right: cond.alt.take(),
-                    });
+                });
-                    return;
+                return;
-                }
             }
         }
 
@@ -145,7 +243,7 @@ impl Optimizer<'_> {
         if let Known(Type::Bool) = rt {
             let rb = cond.alt.as_pure_bool();
             if let Known(false) = rb {
-                log::trace!("conditionals: `foo ? 1 : false` => `!!foo && 1`");
+                log::debug!("conditionals: `foo ? bar : false` => `!!foo && bar`");
                 self.changed = true;
 
                 // Negate twice to convert `test` to boolean.
@@ -159,6 +257,22 @@ impl Optimizer<'_> {
                 });
                 return;
             }
+
+            if let Known(true) = rb {
+                log::debug!("conditionals: `foo ? bar : true` => `!foo || bar");
+                self.changed = true;
+
+                // Negate twice to convert `test` to boolean.
+                self.negate(&mut cond.test);
+
+                *e = Expr::Bin(BinExpr {
+                    span: cond.span,
+                    op: op!("||"),
+                    left: cond.test.take(),
+                    right: cond.cons.take(),
+                });
+                return;
+            }
         }
     }
 
@@ -199,7 +313,7 @@ impl Optimizer<'_> {
         }
 
         self.changed = true;
-        log::trace!("conditionals: Merging if statements with same `cons`");
+        log::debug!("conditionals: Merging if statements with same `cons`");
 
         let mut cur: Option<IfStmt> = None;
         let mut new = Vec::with_capacity(stmts.len());
@@ -272,15 +386,28 @@ impl Optimizer<'_> {
     /// }
     /// ```
     pub(super) fn compress_if_stmt_as_cond(&mut self, s: &mut Stmt) {
-        if !self.options.conditionals {
-            return;
-        }
-
         let stmt = match s {
             Stmt::If(v) => v,
             _ => return,
         };
 
+        match &*stmt.cons {
+            Stmt::Empty(..) => {
+                if self.options.conditionals || self.options.unused {
+                    if stmt.alt.is_none() {
+                        *s = Stmt::Expr(ExprStmt {
+                            span: stmt.span,
+                            expr: stmt.test.take(),
+                        });
+                        self.changed = true;
+                        log::debug!("conditionals: `if (foo);` => `foo` ");
+                        return;
+                    }
+                }
+            }
+            _ => {}
+        }
+
         // If alt does not exist, an if statement is better than a conditional
         // expression.
         let alt = match &mut stmt.alt {
@@ -303,7 +430,7 @@ impl Optimizer<'_> {
                     Expr::Unary(UnaryExpr {
                         op: op!("!"), arg, ..
                     }) => {
-                        log::trace!("Optimizing `if (!foo); else bar();` as `foo && bar();`");
+                        log::debug!("Optimizing `if (!foo); else bar();` as `foo && bar();`");
 
                         let mut expr = Box::new(Expr::Bin(BinExpr {
                             span: DUMMY_SP,
@@ -318,7 +445,7 @@ impl Optimizer<'_> {
                         });
                     }
                     _ => {
-                        log::trace!("Optimizing `if (foo); else bar();` as `foo || bar();`");
+                        log::debug!("Optimizing `if (foo); else bar();` as `foo || bar();`");
 
                         let mut expr = Box::new(Expr::Bin(BinExpr {
                             span: DUMMY_SP,
@@ -356,29 +483,27 @@ impl Optimizer<'_> {
             None => {}
         }
 
-        // if (a) b(); else c(); => a ? b() : c()
+        if self.options.conditionals || self.options.bools {
-        log::trace!(
+            // if (a) b(); else c(); => a ? b() : c()
-            "Compressing if statement as conditional expression (even though cons and alt is not \
+            log::debug!(
-             compressable)"
+                "Compressing if statement as conditional expression (even though cons and alt is \
-        );
+                 not compressable)"
-        self.changed = true;
+            );
-        *s = Stmt::Expr(ExprStmt {
+            self.changed = true;
-            span: stmt.span.with_mark(self.done),
+            *s = Stmt::Expr(ExprStmt {
-            expr: Box::new(Expr::Cond(CondExpr {
+                span: stmt.span.with_mark(self.done),
-                span: DUMMY_SP.with_ctxt(self.done_ctxt),
+                expr: Box::new(Expr::Cond(CondExpr {
-                test: stmt.test.take(),
+                    span: DUMMY_SP.with_ctxt(self.done_ctxt),
-                cons: Box::new(cons.take()),
+                    test: stmt.test.take(),
-                alt: Box::new(alt.take()),
+                    cons: Box::new(cons.take()),
-            })),
+                    alt: Box::new(alt.take()),
-        })
+                })),
+            })
+        }
     }
 
     /// Compress a conditional expression if cons and alt is simillar
     pub(super) fn compress_cond_expr_if_simillar(&mut self, e: &mut Expr) {
-        if !self.options.conditionals {
-            return;
-        }
-
         let cond = match e {
             Expr::Cond(expr) => expr,
             _ => return,
@@ -398,7 +523,7 @@ impl Optimizer<'_> {
 
         // x ? x : y => x || y
         if cond.test.is_ident() && cond.test.eq_ignore_span(&cond.cons) {
-            log::trace!("Compressing `x ? x : y` as `x || y`");
+            log::debug!("Compressing `x ? x : y` as `x || y`");
             self.changed = true;
             *e = Expr::Bin(BinExpr {
                 span: cond.span,
@@ -417,43 +542,24 @@ impl Optimizer<'_> {
         alt: &mut Expr,
         is_for_if_stmt: bool,
     ) -> Option<Expr> {
-        if cons.eq_ignore_span(alt) {
+        if cons.eq_ignore_span(alt)
+            && match &*cons {
+                Expr::Yield(..) | Expr::Fn(..) => false,
+                _ => true,
+            }
+        {
+            log::debug!("conditionals: cons is same as alt");
             return Some(Expr::Seq(SeqExpr {
                 span: DUMMY_SP,
                 exprs: vec![test.take(), Box::new(cons.take())],
             }));
         }
 
-        match &**test {
-            Expr::Call(CallExpr {
-                callee: ExprOrSuper::Expr(callee),
-                ..
-            }) => match &**callee {
-                Expr::Ident(callee) => {
-                    let side_effect_free = self
-                        .data
-                        .as_ref()
-                        .and_then(|data| data.vars.get(&callee.to_id()))
-                        .map(|v| v.is_fn_local)
-                        .unwrap_or(false);
-                    if !side_effect_free {
-                        match cons {
-                            Expr::Call(..) => {
-                                return None;
-                            }
-                            _ => {}
-                        }
-                    }
-                }
-                _ => return None,
-            },
-            _ => {}
-        }
-
         match (cons, alt) {
             (Expr::Call(cons), Expr::Call(alt)) => {
                 let cons_callee = cons.callee.as_expr().and_then(|e| e.as_ident())?;
                 //
+
                 if !cons.callee.eq_ignore_span(&alt.callee) {
                     return None;
                 }
@@ -462,7 +568,7 @@ impl Optimizer<'_> {
                     .data
                     .as_ref()
                     .and_then(|data| data.vars.get(&cons_callee.to_id()))
-                    .map(|v| v.is_fn_local)
+                    .map(|v| v.is_fn_local && v.declared)
                     .unwrap_or(false);
 
                 if side_effect_free
@@ -476,8 +582,9 @@ impl Optimizer<'_> {
                         .zip(alt.args.iter())
                         .filter(|(cons, alt)| !cons.eq_ignore_span(alt))
                         .count();
+
                     if diff_count == 1 {
-                        log::trace!(
+                        log::debug!(
                             "conditionals: Merging cons and alt as only one argument differs"
                         );
                         self.changed = true;
@@ -543,7 +650,7 @@ impl Optimizer<'_> {
                         })),
                     });
 
-                    log::trace!(
+                    log::debug!(
                         "Compreessing if into cond as there's no side effect and the number of \
                          arguments is 1"
                     );
@@ -556,7 +663,7 @@ impl Optimizer<'_> {
                 }
 
                 if !side_effect_free && is_for_if_stmt {
-                    log::trace!("Compreessing if into cond while preserving side effects");
+                    log::debug!("Compreessing if into cond while preserving side effects");
                     return Some(Expr::Cond(CondExpr {
                         span: DUMMY_SP.with_ctxt(self.done_ctxt),
                         test: test.take(),
@@ -601,7 +708,7 @@ impl Optimizer<'_> {
                             })),
                         });
 
-                        log::trace!(
+                        log::debug!(
                             "Compreessing if statement into a condiotnal expression of `new` as \
                              there's no side effect and the number of arguments is 1"
                         );
@@ -623,7 +730,7 @@ impl Optimizer<'_> {
                     && cons.left.eq_ignore_span(&alt.left)
                     && is_simple_lhs(&cons.left) =>
             {
-                log::trace!("Merging assignments in cons and alt of if statement");
+                log::debug!("Merging assignments in cons and alt of if statement");
                 Some(Expr::Assign(AssignExpr {
                     span: DUMMY_SP,
                     op: cons.op,
@@ -639,7 +746,7 @@ impl Optimizer<'_> {
 
             // a ? b ? c() : d() : d() => a && b ? c() : d()
             (Expr::Cond(cons), alt) if (*cons.alt).eq_ignore_span(&*alt) => {
-                log::trace!("conditionals: a ? b ? c() : d() : d() => a && b ? c() : d()");
+                log::debug!("conditionals: a ? b ? c() : d() : d() => a && b ? c() : d()");
                 return Some(Expr::Cond(CondExpr {
                     span: DUMMY_SP.with_ctxt(self.done_ctxt),
                     test: Box::new(Expr::Bin(BinExpr {
@@ -656,16 +763,19 @@ impl Optimizer<'_> {
             // z ? "fuji" : (condition(), "fuji");
             // =>
             // (z || condition(), "fuji");
-            (cons, Expr::Seq(alt))
+            (cons, Expr::Seq(alt)) if (**alt.exprs.last().unwrap()).eq_ignore_span(&*cons) => {
-                if alt.exprs.len() == 2 && (**alt.exprs.last().unwrap()).eq_ignore_span(&*cons) =>
+                self.changed = true;
-            {
+                log::debug!("conditionals: Reducing seq expr in alt");
-                log::trace!("conditionals: Reducing seq expr in alt");
                 //
+                alt.exprs.pop();
                 let first = Box::new(Expr::Bin(BinExpr {
                     span: DUMMY_SP,
                     left: test.take(),
                     op: op!("||"),
-                    right: alt.exprs[0].take(),
+                    right: Box::new(Expr::Seq(SeqExpr {
+                        span: alt.span,
+                        exprs: alt.exprs.take(),
+                    })),
                 }));
                 return Some(Expr::Seq(SeqExpr {
                     span: DUMMY_SP,
@@ -673,9 +783,164 @@ impl Optimizer<'_> {
                 }));
             }
 
+            // z ? (condition(), "fuji") : "fuji"
+            // =>
+            // (z && condition(), "fuji");
+            (Expr::Seq(cons), alt) if (**cons.exprs.last().unwrap()).eq_ignore_span(&*alt) => {
+                self.changed = true;
+                log::debug!("conditionals: Reducing seq expr in cons");
+                //
+                cons.exprs.pop();
+                let first = Box::new(Expr::Bin(BinExpr {
+                    span: DUMMY_SP,
+                    left: test.take(),
+                    op: op!("&&"),
+                    right: Box::new(Expr::Seq(SeqExpr {
+                        span: cons.span,
+                        exprs: cons.exprs.take(),
+                    })),
+                }));
+                return Some(Expr::Seq(SeqExpr {
+                    span: DUMMY_SP,
+                    exprs: vec![first, Box::new(alt.take())],
+                }));
+            }
+
             _ => None,
         }
     }
+
+    /// Currently disabled.
+    pub(super) fn inject_else(&mut self, stmts: &mut Vec<Stmt>) {
+        if DISABLE_BUGGY_PASSES {
+            return;
+        }
+
+        let len = stmts.len();
+
+        let pos_of_if = stmts.iter().enumerate().rposition(|(idx, s)| {
+            idx != len - 1
+                && match s {
+                    Stmt::If(IfStmt {
+                        cons, alt: None, ..
+                    }) => match &**cons {
+                        Stmt::Block(b) => {
+                            b.stmts.len() == 2
+                                && match b.stmts.first() {
+                                    Some(Stmt::If(..) | Stmt::Expr(..)) => false,
+                                    _ => true,
+                                }
+                                && match b.stmts.last() {
+                                    Some(Stmt::Return(ReturnStmt { arg: None, .. })) => true,
+                                    _ => false,
+                                }
+                        }
+                        _ => false,
+                    },
+                    _ => false,
+                }
+        });
+
+        let pos_of_if = match pos_of_if {
+            Some(v) => v,
+            _ => return,
+        };
+
+        self.changed = true;
+        log::debug!("if_return: Injecting else because it's shorter");
+
+        let mut new = vec![];
+        new.reserve(pos_of_if + 1);
+        new.extend(stmts.drain(..pos_of_if));
+        let alt = stmts.drain(1..).collect::<Vec<_>>();
+
+        let if_stmt = stmts.take().into_iter().next().unwrap();
+        match if_stmt {
+            Stmt::If(mut s) => {
+                match &mut *s.cons {
+                    Stmt::Block(cons) => {
+                        cons.stmts.pop();
+                    }
+                    _ => {
+                        unreachable!()
+                    }
+                }
+
+                assert_eq!(s.alt, None);
+
+                s.alt = Some(if alt.len() == 1 {
+                    Box::new(alt.into_iter().next().unwrap())
+                } else {
+                    Box::new(Stmt::Block(BlockStmt {
+                        span: DUMMY_SP,
+                        stmts: alt,
+                    }))
+                });
+
+                new.push(Stmt::If(s))
+            }
+            _ => {
+                unreachable!()
+            }
+        }
+
+        *stmts = new;
+    }
+
+    /// if (foo) return bar()
+    /// else baz()
+    ///
+    /// `else` token can be removed from the code above.
+    pub(super) fn drop_else_token<T>(&mut self, stmts: &mut Vec<T>)
+    where
+        T: StmtLike,
+    {
+        // Find an if statement with else token.
+        let need_work = stmts.iter().any(|stmt| match stmt.as_stmt() {
+            Some(Stmt::If(IfStmt {
+                cons,
+                alt: Some(..),
+                ..
+            })) => always_terminates(cons),
+            _ => false,
+        });
+        if !need_work {
+            return;
+        }
+        //
+
+        let mut new_stmts = vec![];
+
+        for stmt in stmts.take() {
+            match stmt.try_into_stmt() {
+                Ok(stmt) => match stmt {
+                    Stmt::If(IfStmt {
+                        span,
+                        test,
+                        cons,
+                        alt: Some(alt),
+                        ..
+                    }) if always_terminates(&cons) => {
+                        new_stmts.push(T::from_stmt(Stmt::If(IfStmt {
+                            span,
+                            test,
+                            cons,
+                            alt: None,
+                        })));
+                        new_stmts.push(T::from_stmt(*alt));
+                    }
+                    _ => {
+                        new_stmts.push(T::from_stmt(stmt));
+                    }
+                },
+                Err(stmt) => new_stmts.push(stmt),
+            }
+        }
+
+        self.changed = true;
+        log::debug!("conditionals: Dropped useless `else` token");
+        *stmts = new_stmts;
+    }
 }
 
 fn extract_expr_stmt(s: &mut Stmt) -> Option<&mut Expr> {
@@ -693,7 +958,23 @@ fn is_simple_lhs(l: &PatOrExpr) -> bool {
         },
         PatOrExpr::Pat(l) => match &**l {
             Pat::Ident(_) => return true,
+            Pat::Expr(e) => match &**e {
+                Expr::Ident(..) => return true,
+                _ => false,
+            },
             _ => false,
         },
     }
 }
+
+pub(super) fn always_terminates(s: &Stmt) -> bool {
+    match s {
+        Stmt::Return(..) | Stmt::Throw(..) | Stmt::Break(..) | Stmt::Continue(..) => true,
+        Stmt::If(IfStmt { cons, alt, .. }) => {
+            always_terminates(&cons) && alt.as_deref().map(always_terminates).unwrap_or(false)
+        }
+        Stmt::Block(s) => s.stmts.iter().any(always_terminates),
+
+        _ => false,
+    }
+}

ecmascript/minifier/src/compress/optimize/dead_code.rs

@@ -55,7 +55,7 @@ impl Optimizer<'_> {
                                 .map(|var| var.is_fn_local)
                                 .unwrap_or(false)
                             {
-                                log::trace!(
+                                log::debug!(
                                     "dead_code: Dropping an assigment to a varaible declared in \
                                      function because function is being terminated"
                                 );

ecmascript/minifier/src/compress/optimize/evaluate.rs

@@ -65,7 +65,7 @@ impl Optimizer<'_> {
                 sym: js_word!("undefined"),
                 ..
             }) => {
-                log::trace!("evaluate: `undefined` -> `void 0`");
+                log::debug!("evaluate: `undefined` -> `void 0`");
                 self.changed = true;
                 *e = *undefined(*span);
                 return;
@@ -76,7 +76,7 @@ impl Optimizer<'_> {
                 sym: js_word!("Infinity"),
                 ..
             }) => {
-                log::trace!("evaluate: `Infinity` -> `1 / 0`");
+                log::debug!("evaluate: `Infinity` -> `1 / 0`");
                 self.changed = true;
                 *e = Expr::Bin(BinExpr {
                     span: span.with_ctxt(self.done_ctxt),
@@ -149,7 +149,7 @@ impl Optimizer<'_> {
                     1 => match &*args[0].expr {
                         Expr::Lit(Lit::Str(exp)) => {
                             self.changed = true;
-                            log::trace!(
+                            log::debug!(
                                 "evaluate: Converting RegExpr call into a regexp literal `/{}/`",
                                 exp.value
                             );
@@ -165,7 +165,7 @@ impl Optimizer<'_> {
                     _ => match (&*args[0].expr, &*args[1].expr) {
                         (Expr::Lit(Lit::Str(exp)), Expr::Lit(Lit::Str(flags))) => {
                             self.changed = true;
-                            log::trace!(
+                            log::debug!(
                                 "evaluate: Converting RegExpr call into a regexp literal `/{}/{}`",
                                 exp.value,
                                 flags.value
@@ -209,7 +209,7 @@ impl Optimizer<'_> {
                                 match char::from_u32(v) {
                                     Some(v) => {
                                         self.changed = true;
-                                        log::trace!(
+                                        log::debug!(
                                             "evanluate: Evaluated `String.charCodeAt({})` as `{}`",
                                             char_code,
                                             v
@@ -362,7 +362,7 @@ impl Optimizer<'_> {
                     match c {
                         Some(v) => {
                             self.changed = true;
-                            log::trace!(
+                            log::debug!(
                                 "evaluate: Evaluated `charCodeAt` of a string literal as `{}`",
                                 v
                             );
@@ -373,7 +373,7 @@ impl Optimizer<'_> {
                         }
                         None => {
                             self.changed = true;
-                            log::trace!(
+                            log::debug!(
                                 "evaluate: Evaluated `charCodeAt` of a string literal as `NaN`",
                             );
                             *e = Expr::Ident(Ident::new(
@@ -389,7 +389,7 @@ impl Optimizer<'_> {
         };
 
         self.changed = true;
-        log::trace!("evaluate: Evaluated `{}` of a string literal", method);
+        log::debug!("evaluate: Evaluated `{}` of a string literal", method);
         *e = Expr::Lit(Lit::Str(Str {
             value: new_val.into(),
             ..s
@@ -412,7 +412,7 @@ impl Optimizer<'_> {
                                 ..
                             }) => {
                                 self.changed = true;
-                                log::trace!(
+                                log::debug!(
                                     "evaluate: Reducing a call to `Number` into an unary operation"
                                 );
 
@@ -442,7 +442,7 @@ impl Optimizer<'_> {
             Expr::Call(..) => {
                 if let Some(value) = self.eval_as_number(&e) {
                     self.changed = true;
-                    log::trace!("evaluate: Evaluated an expression as `{}`", value);
+                    log::debug!("evaluate: Evaluated an expression as `{}`", value);
 
                     *e = Expr::Lit(Lit::Num(Number {
                         span: e.span(),
@@ -462,7 +462,7 @@ impl Optimizer<'_> {
                 if let Known(l) = l {
                     if let Known(r) = r {
                         self.changed = true;
-                        log::trace!("evaluate: Evaulated `{:?} ** {:?}`", l, r);
+                        log::debug!("evaluate: Evaulated `{:?} ** {:?}`", l, r);
 
                         let value = l.powf(r);
                         *e = Expr::Lit(Lit::Num(Number {
@@ -507,7 +507,7 @@ impl Optimizer<'_> {
                                 }
 
                                 self.changed = true;
-                                log::trace!("evaluate: `0 / 0` => `NaN`");
+                                log::debug!("evaluate: `0 / 0` => `NaN`");
 
                                 // Sign does not matter for NaN
                                 *e = Expr::Ident(Ident::new(
@@ -518,7 +518,7 @@ impl Optimizer<'_> {
                             }
                             (FpCategory::Normal, FpCategory::Zero) => {
                                 self.changed = true;
-                                log::trace!("evaluate: `constant / 0` => `Infinity`");
+                                log::debug!("evaluate: `constant / 0` => `Infinity`");
 
                                 // Sign does not matter for NaN
                                 *e = if ln.is_sign_positive() == rn.is_sign_positive() {
@@ -590,7 +590,7 @@ impl Optimizer<'_> {
                     let value = num_to_fixed(num.value, precision + 1);
 
                     self.changed = true;
-                    log::trace!(
+                    log::debug!(
                         "evaluate: Evaluating `{}.toFixed({})` as `{}`",
                         num,
                         precision,
@@ -816,7 +816,7 @@ impl Optimizer<'_> {
                         match call.args.len() {
                             0 => {
                                 self.changed = true;
-                                log::trace!("evaluate: Dropping array.slice call");
+                                log::debug!("evaluate: Dropping array.slice call");
                                 *e = *obj.take();
                                 return;
                             }
@@ -825,7 +825,7 @@ impl Optimizer<'_> {
                                     let start = start.floor() as usize;
 
                                     self.changed = true;
-                                    log::trace!("evaluate: Reducing array.slice({}) call", start);
+                                    log::debug!("evaluate: Reducing array.slice({}) call", start);
 
                                     if start >= arr.elems.len() {
                                         *e = Expr::Array(ArrayLit {
@@ -850,7 +850,7 @@ impl Optimizer<'_> {
                                     if let Known(end) = end {
                                         let end = end.floor() as usize;
                                         self.changed = true;
-                                        log::trace!(
+                                        log::debug!(
                                             "evaluate: Reducing array.slice({}, {}) call",
                                             start,
                                             end
@@ -936,7 +936,7 @@ impl Optimizer<'_> {
                         }
 
                         self.changed = true;
-                        log::trace!(
+                        log::debug!(
                             "evaludate: Reduced `funtion.valueOf()` into a function expression"
                         );
 
@@ -977,7 +977,7 @@ impl Optimizer<'_> {
                     // As we used as_pure_bool, we can drop it.
                     if v && e.op == op!("&&") {
                         self.changed = true;
-                        log::trace!("Removing `b` from `a && b && c` because b is always truthy");
+                        log::debug!("Removing `b` from `a && b && c` because b is always truthy");
 
                         left.right.take();
                         return;
@@ -985,7 +985,7 @@ impl Optimizer<'_> {
 
                     if !v && e.op == op!("||") {
                         self.changed = true;
-                        log::trace!("Removing `b` from `a || b || c` because b is always falsy");
+                        log::debug!("Removing `b` from `a || b || c` because b is always falsy");
 
                         left.right.take();
                         return;
@@ -1011,7 +1011,7 @@ impl Optimizer<'_> {
                 //
                 if is_pure_undefined_or_null(&obj) {
                     self.changed = true;
-                    log::trace!(
+                    log::debug!(
                         "evaluate: Reduced an optioanl chaining operation because object is \
                          always null or undefined"
                     );
@@ -1028,7 +1028,7 @@ impl Optimizer<'_> {
             }) => {
                 if is_pure_undefined_or_null(&callee) {
                     self.changed = true;
-                    log::trace!(
+                    log::debug!(
                         "evaluate: Reduced a call expression with optioanl chaining operation \
                          because object is always null or undefined"
                     );

ecmascript/minifier/src/compress/optimize/fns.rs

@@ -0,0 +1,97 @@
+use super::Optimizer;
+use crate::util::{sort::is_sorted_by, MoudleItemExt};
+use std::cmp::Ordering;
+use swc_ecma_ast::*;
+use swc_ecma_transforms_base::ext::MapWithMut;
+
+impl Optimizer<'_> {
+    /// Calls `reorder_stmts_inner` after splitting stmts.
+    pub(super) fn reorder_stmts<T>(&mut self, stmts: &mut Vec<T>)
+    where
+        T: MoudleItemExt,
+    {
+        if self.ctx.in_asm {
+            return;
+        }
+
+        self.reorder_stmts_inner(stmts);
+    }
+
+    /// Sorts given statements.
+    fn reorder_stmts_inner<T>(&mut self, stmts: &mut Vec<T>)
+    where
+        T: MoudleItemExt,
+    {
+        if !self.options.join_vars {
+            return;
+        }
+
+        // Sort by position
+
+        if is_sorted_by(stmts.iter(), |a, b| {
+            // Check for function declarations.
+
+            match (a.as_module_decl(), b.as_module_decl()) {
+                (
+                    Err(Stmt::Decl(
+                        Decl::Fn(..)
+                        | Decl::Var(VarDecl {
+                            kind: VarDeclKind::Var,
+                            ..
+                        }),
+                    )),
+                    Err(Stmt::Decl(
+                        Decl::Fn(..)
+                        | Decl::Var(VarDecl {
+                            kind: VarDeclKind::Var,
+                            ..
+                        }),
+                    )),
+                ) => Some(Ordering::Less),
+                (_, Err(Stmt::Decl(Decl::Fn(..)))) => Some(Ordering::Greater),
+                _ => Some(Ordering::Less),
+            }
+        }) {
+            return;
+        }
+
+        self.changed = true;
+        log::debug!("fns: Reordering statements");
+        let mut fns = vec![];
+        let mut other = vec![];
+
+        for stmt in stmts.take() {
+            let stmt = stmt.into_module_item();
+
+            match stmt {
+                ModuleItem::Stmt(Stmt::Decl(Decl::Fn(..)))
+                | ModuleItem::ModuleDecl(ModuleDecl::ExportDecl(ExportDecl {
+                    decl: Decl::Fn(..),
+                    ..
+                }))
+                | ModuleItem::Stmt(Stmt::Decl(Decl::Var(VarDecl {
+                    kind: VarDeclKind::Var,
+                    ..
+                })))
+                | ModuleItem::ModuleDecl(ModuleDecl::ExportDecl(ExportDecl {
+                    decl:
+                        Decl::Var(VarDecl {
+                            kind: VarDeclKind::Var,
+                            ..
+                        }),
+                    ..
+                })) => {
+                    fns.push(T::from_module_item(stmt));
+                }
+
+                _ => {
+                    other.push(T::from_module_item(stmt));
+                }
+            }
+        }
+
+        fns.extend(other);
+
+        *stmts = fns;
+    }
+}

ecmascript/minifier/src/compress/optimize/hoist_props.rs

@@ -88,7 +88,7 @@ impl Optimizer<'_> {
 
                                     match &p.key {
                                         PropName::Str(s) => {
-                                            log::trace!(
+                                            log::debug!(
                                                 "hoist_props: Storing a varaible to inline \
                                                  properties"
                                             );
@@ -96,7 +96,7 @@ impl Optimizer<'_> {
                                                 .insert((name.to_id(), s.value.clone()), value);
                                         }
                                         PropName::Ident(i) => {
-                                            log::trace!(
+                                            log::debug!(
                                                 "hoist_props: Storing a varaible to inline \
                                                  properties"
                                             );
@@ -118,9 +118,12 @@ impl Optimizer<'_> {
                     .data
                     .as_ref()
                     .and_then(|data| {
-                        data.vars
+                        data.vars.get(&name.to_id()).map(|v| {
-                            .get(&name.to_id())
+                            v.ref_count == 1
-                            .map(|v| v.ref_count == 1 && v.has_property_access)
+                                && v.has_property_access
+                                && v.is_fn_local
+                                && !v.used_in_loop
+                        })
                     })
                     .unwrap_or(false)
                 {
@@ -132,6 +135,15 @@ impl Optimizer<'_> {
                     None => return,
                 };
 
+                match &*init {
+                    Expr::This(..) => {
+                        n.init = Some(init);
+                        return;
+                    }
+
+                    _ => {}
+                }
+
                 match self.vars_for_prop_hoisting.insert(name.to_id(), init) {
                     Some(prev) => {
                         panic!(
@@ -140,7 +152,13 @@ impl Optimizer<'_> {
                             prev
                         );
                     }
-                    None => {}
+                    None => {
+                        log::debug!(
+                            "hoist_props: Stored {}{:?} to inline property access",
+                            name.id.sym,
+                            name.id.span.ctxt
+                        );
+                    }
                 }
             }
             _ => {}
@@ -161,7 +179,7 @@ impl Optimizer<'_> {
                     if let Some(value) = self.vars_for_prop_hoisting.remove(&obj.to_id()) {
                         member.obj = ExprOrSuper::Expr(value);
                         self.changed = true;
-                        log::trace!("hoist_props: Inlined a property");
+                        log::debug!("hoist_props: Inlined a property");
                         return;
                     }
 
@@ -174,7 +192,7 @@ impl Optimizer<'_> {
                             if let Some(value) =
                                 self.simple_props.get(&(obj.to_id(), prop.sym.clone()))
                             {
-                                log::trace!("hoist_props: Inlining `{}.{}`", obj.sym, prop.sym);
+                                log::debug!("hoist_props: Inlining `{}.{}`", obj.sym, prop.sym);
                                 self.changed = true;
                                 *e = *value.clone()
                             }

ecmascript/minifier/src/compress/optimize/if_return.rs

@@ -1,9 +1,12 @@
 use super::Optimizer;
 use crate::compress::optimize::is_pure_undefined;
+use crate::debug::dump;
 use crate::util::ExprOptExt;
+use swc_common::Spanned;
 use swc_common::DUMMY_SP;
 use swc_ecma_ast::*;
 use swc_ecma_transforms_base::ext::MapWithMut;
+use swc_ecma_utils::prepend;
 use swc_ecma_utils::undefined;
 use swc_ecma_utils::StmtLike;
 use swc_ecma_visit::noop_visit_type;
@@ -14,6 +17,216 @@ use swc_ecma_visit::VisitWith;
 /// Methods related to the option `if_return`. All methods are noop if
 /// `if_return` is false.
 impl Optimizer<'_> {
+    pub(super) fn drop_undefined_from_return_arg(&mut self, s: &mut ReturnStmt) {
+        match s.arg.as_deref() {
+            Some(e) => {
+                if is_pure_undefined(e) {
+                    self.changed = true;
+                    log::debug!("Dropped `undefined` from `return undefined`");
+                    s.arg.take();
+                }
+            }
+            None => {}
+        }
+    }
+
+    /// # Input
+    ///
+    /// ```js
+    /// function f(a, b) {
+    ///     if (a) return;
+    ///     console.log(b);
+    /// }
+    /// ```
+    ///
+    /// # Output
+    /// ```js
+    /// function f(a, b) {
+    ///     if (!a)
+    ///         console.log(b);
+    /// }
+    /// ```
+    pub(super) fn negate_if_terminate(
+        &mut self,
+        stmts: &mut Vec<Stmt>,
+        handle_return: bool,
+        handle_continue: bool,
+    ) {
+        if handle_return {
+            if !self.options.if_return || !self.options.bools {
+                return;
+            }
+
+            for s in stmts.iter_mut() {
+                match s {
+                    Stmt::If(s) => match &mut *s.cons {
+                        Stmt::Block(cons) => {
+                            self.negate_if_terminate(&mut cons.stmts, true, false);
+                        }
+                        _ => {}
+                    },
+                    _ => {}
+                }
+            }
+        }
+
+        let len = stmts.len();
+
+        let pos_of_if = stmts.iter().enumerate().rposition(|(idx, s)| {
+            idx != len - 1
+                && match s {
+                    Stmt::If(IfStmt {
+                        cons, alt: None, ..
+                    }) => match &**cons {
+                        Stmt::Return(ReturnStmt { arg: None, .. }) => handle_return,
+
+                        Stmt::Continue(ContinueStmt { label: None, .. }) => handle_continue,
+                        _ => false,
+                    },
+                    _ => false,
+                }
+        });
+
+        let pos_of_if = match pos_of_if {
+            Some(v) => v,
+            _ => return,
+        };
+
+        self.changed = true;
+        log::debug!(
+            "if_return: Negating `foo` in `if (foo) return; bar()` to make it `if (!foo) bar()`"
+        );
+
+        let mut new = vec![];
+        new.extend(stmts.drain(..pos_of_if));
+        let cons = stmts.drain(1..).collect::<Vec<_>>();
+
+        let if_stmt = stmts.take().into_iter().next().unwrap();
+        match if_stmt {
+            Stmt::If(mut s) => {
+                assert_eq!(s.alt, None);
+                self.negate(&mut s.test);
+
+                s.cons = if cons.len() == 1 {
+                    Box::new(cons.into_iter().next().unwrap())
+                } else {
+                    Box::new(Stmt::Block(BlockStmt {
+                        span: DUMMY_SP,
+                        stmts: cons,
+                    }))
+                };
+
+                new.push(Stmt::If(s))
+            }
+            _ => {
+                unreachable!()
+            }
+        }
+
+        *stmts = new;
+    }
+
+    pub(super) fn merge_nested_if(&mut self, s: &mut IfStmt) {
+        if !self.options.conditionals && !self.options.bools {
+            return;
+        }
+
+        if s.alt.is_some() {
+            return;
+        }
+
+        match &mut *s.cons {
+            Stmt::If(IfStmt {
+                test,
+                cons,
+                alt: None,
+                ..
+            }) => {
+                self.changed = true;
+                log::debug!("if_return: Merging nested if statements");
+
+                s.test = Box::new(Expr::Bin(BinExpr {
+                    span: s.test.span(),
+                    op: op!("&&"),
+                    left: s.test.take(),
+                    right: test.take(),
+                }));
+                s.cons = cons.take();
+            }
+            _ => {}
+        }
+    }
+
+    pub(super) fn merge_else_if(&mut self, s: &mut IfStmt) {
+        match s.alt.as_deref_mut() {
+            Some(Stmt::If(IfStmt {
+                span: span_of_alt,
+                test: test_of_alt,
+                cons: cons_of_alt,
+                alt: Some(alt_of_alt),
+                ..
+            })) => {
+                match &**cons_of_alt {
+                    Stmt::Return(..) | Stmt::Continue(ContinueStmt { label: None, .. }) => {}
+                    _ => return,
+                }
+
+                match &mut **alt_of_alt {
+                    Stmt::Block(..) => {}
+                    Stmt::Expr(..) => {
+                        *alt_of_alt = Box::new(Stmt::Block(BlockStmt {
+                            span: DUMMY_SP,
+                            stmts: vec![*alt_of_alt.take()],
+                        }));
+                    }
+                    _ => {
+                        return;
+                    }
+                }
+
+                self.changed = true;
+                log::debug!("if_return: Merging `else if` into `else`");
+
+                match &mut **alt_of_alt {
+                    Stmt::Block(alt_of_alt) => {
+                        prepend(
+                            &mut alt_of_alt.stmts,
+                            Stmt::If(IfStmt {
+                                span: *span_of_alt,
+                                test: test_of_alt.take(),
+                                cons: cons_of_alt.take(),
+                                alt: None,
+                            }),
+                        );
+                    }
+
+                    _ => {
+                        unreachable!()
+                    }
+                }
+
+                s.alt = Some(alt_of_alt.take());
+                return;
+            }
+
+            _ => {}
+        }
+    }
+
+    fn merge_nested_if_returns(&mut self, s: &mut Stmt) {
+        match s {
+            Stmt::Block(s) => self.merge_if_returns(&mut s.stmts),
+            Stmt::If(s) => {
+                self.merge_nested_if_returns(&mut s.cons);
+
+                if let Some(alt) = &mut s.alt {
+                    self.merge_nested_if_returns(&mut **alt);
+                }
+            }
+            _ => {}
+        }
+    }
+
     /// Merge simple return statements in if statements.
     ///
     /// # Example
@@ -34,33 +247,94 @@ impl Optimizer<'_> {
     ///     return a ? foo() : bar();
     /// }
     /// ```
-    pub(super) fn merge_if_returns<T>(&mut self, stmts: &mut Vec<T>)
+    pub(super) fn merge_if_returns(&mut self, stmts: &mut Vec<Stmt>) {
-    where
+        if !self.options.if_return {
-        T: StmtLike,
+            return;
-        Vec<T>: VisitWith<ReturnFinder>,
+        }
-    {
+
-        if !self.options.if_return || stmts.is_empty() {
+        for stmt in stmts.iter_mut() {
+            self.merge_nested_if_returns(stmt)
+        }
+
+        if stmts.len() <= 1 {
+            return;
+        }
+
+        let idx_of_not_mergable = stmts.iter().rposition(|stmt| match stmt.as_stmt() {
+            Some(v) => !self.can_merge_stmt_as_if_return(v),
+            None => true,
+        });
+        let skip = idx_of_not_mergable.map(|v| v + 1).unwrap_or(0);
+        log::trace!("if_return: Skip = {}", skip);
+
+        if stmts.len() <= skip + 1 {
+            log::trace!("if_return: [x] Aborting because of skip");
             return;
         }
 
         {
-            let return_count = count_leaping_returns(&*stmts);
+            let stmts = &stmts[skip..];
+            let return_count: usize = stmts.iter().map(|v| count_leaping_returns(v)).sum();
 
-            let ends_with_if = stmts
+            // There's no return statment so merging requires injecting unnecessary `void 0`
-                .last()
+            if return_count == 0 {
-                .map(|stmt| match stmt.as_stmt() {
+                log::trace!("if_return: [x] Aborting because we failed to find return");
-                    Some(Stmt::If(..)) => true,
+                return;
+            }
+
+            // If the last statement is a return statement and last - 1 is an if statement
+            // is without return, we don't need to fold it as `void 0` is too much for such
+            // cases.
+
+            let if_return_count = stmts
+                .iter()
+                .filter(|s| match s {
+                    Stmt::If(IfStmt {
+                        cons, alt: None, ..
+                    }) => always_terminates_with_return_arg(&cons),
                     _ => false,
                 })
-                .unwrap();
+                .count();
-            if return_count <= 1 && ends_with_if {
+
-                return;
+            if stmts.len() >= 2 {
+                match (
+                    &stmts[stmts.len() - 2].as_stmt(),
+                    &stmts[stmts.len() - 1].as_stmt(),
+                ) {
+                    (_, Some(Stmt::If(IfStmt { alt: None, .. }) | Stmt::Expr(..)))
+                        if if_return_count <= 1 =>
+                    {
+                        log::trace!(
+                            "if_return: [x] Aborting because last stmt is a not return stmt"
+                        );
+                        return;
+                    }
+
+                    (
+                        Some(Stmt::If(IfStmt {
+                            cons, alt: None, ..
+                        })),
+                        Some(Stmt::Return(..)),
+                    ) => match &**cons {
+                        Stmt::Return(ReturnStmt { arg: Some(..), .. }) => {}
+                        _ => {
+                            log::trace!(
+                                "if_return: [x] Aborting because stmt before last is an if stmt \
+                                 and cons of it is not a return stmt"
+                            );
+                            return;
+                        }
+                    },
+
+                    _ => {}
+                }
             }
         }
 
         {
             let start = stmts
                 .iter()
+                .skip(skip)
                 .position(|stmt| match stmt.as_stmt() {
                     Some(v) => self.can_merge_stmt_as_if_return(v),
                     None => false,
@@ -70,16 +344,16 @@ impl Optimizer<'_> {
             let ends_with_mergable = stmts
                 .last()
                 .map(|stmt| match stmt.as_stmt() {
-                    Some(Stmt::Return(..)) | Some(Stmt::Expr(..)) => true,
+                    Some(s) => self.can_merge_stmt_as_if_return(s),
                     _ => false,
                 })
                 .unwrap();
 
-            if stmts.len() - start == 1 && ends_with_mergable {
+            if stmts.len() == start + skip + 1 || !ends_with_mergable {
                 return;
             }
 
-            let can_merge = stmts.iter().skip(start).all(|stmt| match stmt.as_stmt() {
+            let can_merge = stmts.iter().skip(skip).all(|stmt| match stmt.as_stmt() {
                 Some(s) => self.can_merge_stmt_as_if_return(s),
                 _ => false,
             });
@@ -88,28 +362,33 @@ impl Optimizer<'_> {
             }
         }
 
-        log::trace!("if_return: Merging returns");
+        log::debug!("if_return: Merging returns");
+        if cfg!(feature = "debug") {
+            let block = BlockStmt {
+                span: DUMMY_SP,
+                stmts: stmts.clone(),
+            };
+            log::trace!("if_return: {}", dump(&block))
+        }
         self.changed = true;
 
         let mut cur: Option<Box<Expr>> = None;
         let mut new = Vec::with_capacity(stmts.len());
 
-        for stmt in stmts.take() {
+        for (idx, stmt) in stmts.take().into_iter().enumerate() {
-            let stmt = match stmt.try_into_stmt() {
+            if let Some(not_mergable) = idx_of_not_mergable {
-                Ok(stmt) => {
+                if idx < not_mergable {
-                    if !self.can_merge_stmt_as_if_return(&stmt) {
+                    new.push(stmt);
-                        debug_assert_eq!(cur, None);
-                        new.push(T::from_stmt(stmt));
-                        continue;
-                    } else {
-                        stmt
-                    }
-                }
-                Err(item) => {
-                    debug_assert_eq!(cur, None);
-                    new.push(item);
                     continue;
                 }
+            }
+
+            let stmt = if !self.can_merge_stmt_as_if_return(&stmt) {
+                debug_assert_eq!(cur, None);
+                new.push(stmt);
+                continue;
+            } else {
+                stmt
             };
             let is_nonconditional_return = match stmt {
                 Stmt::Return(..) => true,
@@ -203,17 +482,17 @@ impl Optimizer<'_> {
                     let expr = self.ignore_return_value(&mut cur);
 
                     if let Some(cur) = expr {
-                        new.push(T::from_stmt(Stmt::Expr(ExprStmt {
+                        new.push(Stmt::Expr(ExprStmt {
                             span: DUMMY_SP,
                             expr: Box::new(cur),
-                        })))
+                        }))
                     }
                 }
                 _ => {
-                    new.push(T::from_stmt(Stmt::Return(ReturnStmt {
+                    new.push(Stmt::Return(ReturnStmt {
                         span: DUMMY_SP,
                         arg: Some(cur),
-                    })));
+                    }));
                 }
             }
         }
@@ -227,6 +506,11 @@ impl Optimizer<'_> {
     fn merge_if_returns_to(&mut self, stmt: Stmt, mut exprs: Vec<Box<Expr>>) -> Expr {
         //
         match stmt {
+            Stmt::Block(s) => {
+                assert_eq!(s.stmts.len(), 1);
+                self.merge_if_returns_to(s.stmts.into_iter().next().unwrap(), exprs)
+            }
+
             Stmt::If(IfStmt {
                 span,
                 test,
@@ -276,9 +560,10 @@ impl Optimizer<'_> {
     }
 
     fn can_merge_stmt_as_if_return(&self, s: &Stmt) -> bool {
-        match s {
+        let res = match s {
             Stmt::Expr(..) | Stmt::Return(..) => true,
-            Stmt::If(stmt) if self.options.conditionals => {
+            Stmt::Block(s) => s.stmts.len() == 1 && self.can_merge_stmt_as_if_return(&s.stmts[0]),
+            Stmt::If(stmt) => {
                 self.can_merge_stmt_as_if_return(&stmt.cons)
                     && stmt
                         .alt
@@ -287,7 +572,12 @@ impl Optimizer<'_> {
                         .unwrap_or(true)
             }
             _ => false,
-        }
+        };
+        // if !res {
+        //     log::trace!("Cannot merge: {}", dump(s));
+        // }
+
+        res
     }
 }
 
@@ -323,3 +613,19 @@ impl Visit for ReturnFinder {
     fn visit_function(&mut self, _: &Function, _: &dyn Node) {}
     fn visit_arrow_expr(&mut self, _: &ArrowExpr, _: &dyn Node) {}
 }
+
+fn always_terminates_with_return_arg(s: &Stmt) -> bool {
+    match s {
+        Stmt::Return(ReturnStmt { arg: Some(..), .. }) => true,
+        Stmt::If(IfStmt { cons, alt, .. }) => {
+            always_terminates_with_return_arg(&cons)
+                && alt
+                    .as_deref()
+                    .map(always_terminates_with_return_arg)
+                    .unwrap_or(false)
+        }
+        Stmt::Block(s) => s.stmts.iter().any(always_terminates_with_return_arg),
+
+        _ => false,
+    }
+}

ecmascript/minifier/src/compress/optimize/iife.rs

@@ -2,7 +2,6 @@ use super::Optimizer;
 use crate::compress::optimize::Ctx;
 use crate::util::idents_used_by;
 use crate::util::make_number;
-use crate::util::IdentUsageCollector;
 use fxhash::FxHashMap;
 use std::collections::HashMap;
 use std::mem::replace;
@@ -13,20 +12,17 @@ use swc_common::Spanned;
 use swc_common::DUMMY_SP;
 use swc_ecma_ast::*;
 use swc_ecma_transforms_base::ext::MapWithMut;
-use swc_ecma_utils::find_ids;
 use swc_ecma_utils::ident::IdentLike;
 use swc_ecma_utils::undefined;
-use swc_ecma_utils::DestructuringFinder;
+use swc_ecma_utils::ExprFactory;
-use swc_ecma_utils::ExprExt;
 use swc_ecma_utils::Id;
 use swc_ecma_visit::VisitMutWith;
-use swc_ecma_visit::VisitWith;
 
 /// Methods related to the option `negate_iife`.
 impl Optimizer<'_> {
     /// Negates iife, while ignore return value.
     pub(super) fn negate_iife_ignoring_ret(&mut self, e: &mut Expr) {
-        if !self.options.negate_iife || self.ctx.in_bang_arg {
+        if !self.options.negate_iife || self.ctx.in_bang_arg || self.ctx.dont_use_negated_iife {
             return;
         }
 
@@ -42,7 +38,7 @@ impl Optimizer<'_> {
 
         match callee {
             Expr::Fn(..) => {
-                log::trace!("negate_iife: Negating iife");
+                log::debug!("negate_iife: Negating iife");
                 *e = Expr::Unary(UnaryExpr {
                     span: DUMMY_SP,
                     op: op!("!"),
@@ -54,38 +50,72 @@ impl Optimizer<'_> {
         }
     }
 
+    /// Returns true if it did any work.
+    ///
     ///
     /// - `iife ? foo : bar` => `!iife ? bar : foo`
-    pub(super) fn negate_iife_in_cond(&mut self, e: &mut Expr) {
+    pub(super) fn negate_iife_in_cond(&mut self, e: &mut Expr) -> bool {
         let cond = match e {
             Expr::Cond(v) => v,
-            _ => return,
+            _ => return false,
         };
 
         let test_call = match &mut *cond.test {
             Expr::Call(e) => e,
-            _ => return,
+            _ => return false,
         };
 
         let callee = match &mut test_call.callee {
-            ExprOrSuper::Super(_) => return,
+            ExprOrSuper::Super(_) => return false,
             ExprOrSuper::Expr(e) => &mut **e,
         };
 
         match callee {
             Expr::Fn(..) => {
-                log::trace!("negate_iife: Swapping cons and alt");
+                log::debug!("negate_iife: Swapping cons and alt");
                 cond.test = Box::new(Expr::Unary(UnaryExpr {
                     span: DUMMY_SP,
                     op: op!("!"),
                     arg: cond.test.take(),
                 }));
                 swap(&mut cond.cons, &mut cond.alt);
-                return;
+                return true;
             }
-            _ => {}
+            _ => false,
         }
     }
+
+    pub(super) fn restore_negated_iife(&mut self, cond: &mut CondExpr) {
+        if !self.ctx.dont_use_negated_iife {
+            return;
+        }
+
+        match &mut *cond.test {
+            Expr::Unary(UnaryExpr {
+                op: op!("!"), arg, ..
+            }) => match &mut **arg {
+                Expr::Call(CallExpr {
+                    span: call_span,
+                    callee: ExprOrSuper::Expr(callee),
+                    args,
+                    ..
+                }) => match &**callee {
+                    Expr::Fn(..) => {
+                        cond.test = Box::new(Expr::Call(CallExpr {
+                            span: *call_span,
+                            callee: callee.take().as_callee(),
+                            args: args.take(),
+                            type_args: Default::default(),
+                        }));
+                        swap(&mut cond.cons, &mut cond.alt);
+                    }
+                    _ => {}
+                },
+                _ => {}
+            },
+            _ => {}
+        };
+    }
 }
 
 /// Methods related to iife.
@@ -168,21 +198,33 @@ impl Optimizer<'_> {
                         if usage.reassigned {
                             continue;
                         }
+                        if usage.ref_count != 1 {
+                            continue;
+                        }
                     }
 
                     if let Some(arg) = arg {
+                        // NOTE
+                        //
+                        // This function is misdesigned and should be removed.
+                        // This is wrong because the order of execution is not guaranteed.
+                        match &**arg {
+                            Expr::Ident(..) | Expr::Lit(..) => {}
+                            _ => continue,
+                        }
+
                         let should_be_inlined = self.can_be_inlined_for_iife(arg);
                         if should_be_inlined {
-                            log::trace!(
+                            log::debug!(
-                                "iife: Trying to inline {}{:?}",
+                                "iife: Trying to inline argument ({}{:?})",
                                 param.id.sym,
                                 param.id.span.ctxt
                             );
                             vars.insert(param.to_id(), arg.clone());
                         }
                     } else {
-                        log::trace!(
+                        log::debug!(
-                            "iife: Trying to inline {}{:?} (undefined)",
+                            "iife: Trying to inline argument ({}{:?}) (undefined)",
                             param.id.sym,
                             param.id.span.ctxt
                         );
@@ -206,10 +248,11 @@ impl Optimizer<'_> {
         }
     }
 
-    fn inline_vars_in_node<N>(&mut self, n: &mut N, vars: FxHashMap<Id, Box<Expr>>)
+    pub(super) fn inline_vars_in_node<N>(&mut self, n: &mut N, vars: FxHashMap<Id, Box<Expr>>)
     where
         N: VisitMutWith<Self>,
     {
+        log::debug!("inline: inline_vars_in_node");
         let ctx = Ctx {
             inline_prevented: false,
             ..self.ctx
@@ -249,10 +292,6 @@ impl Optimizer<'_> {
             }
         }
 
-        if self.ctx.inline_prevented {
-            return;
-        }
-
         let call = match e {
             Expr::Call(v) => v,
             _ => return,
@@ -267,31 +306,44 @@ impl Optimizer<'_> {
             ExprOrSuper::Expr(e) => &mut **e,
         };
 
-        if call.args.iter().any(|arg| match &*arg.expr {
+        if self.ctx.inline_prevented {
-            Expr::Member(MemberExpr {
+            log::trace!("iife: [x] Inline is prevented");
-                computed: false, ..
-            }) => false,
-            _ => arg.expr.may_have_side_effects(),
-        }) {
             return;
         }
 
         match callee {
             Expr::Arrow(f) => {
+                if self.ctx.in_top_level() && !self.ctx.in_call_arg && self.options.negate_iife {
+                    match &f.body {
+                        BlockStmtOrExpr::BlockStmt(body) => {
+                            let has_decl = body.stmts.iter().any(|stmt| match stmt {
+                                Stmt::Decl(..) => true,
+                                _ => false,
+                            });
+                            if has_decl {
+                                return;
+                            }
+                        }
+                        BlockStmtOrExpr::Expr(_) => {}
+                    }
+                }
+
                 if f.params.iter().any(|param| !param.is_ident()) {
                     return;
                 }
 
-                if is_param_used_by_body(&f.params, &f.body) {
+                let param_ids = f
-                    return;
+                    .params
-                }
+                    .iter()
+                    .map(|p| p.clone().ident().unwrap().id)
+                    .collect::<Vec<_>>();
 
                 match &mut f.body {
                     BlockStmtOrExpr::BlockStmt(body) => {
-                        let new = self.inline_fn_like(body);
+                        let new = self.inline_fn_like(&param_ids, body, &mut call.args);
                         if let Some(new) = new {
                             self.changed = true;
-                            log::trace!("inline: Inlining a function call (arrow)");
+                            log::debug!("inline: Inlining a function call (arrow)");
 
                             *e = new;
                         }
@@ -306,23 +358,6 @@ impl Optimizer<'_> {
                         _ => {}
                     },
                 }
-                let mut inline_map = HashMap::default();
-                for (idx, param) in f.params.iter().enumerate() {
-                    let arg_val = if let Some(arg) = call.args.get(idx) {
-                        arg.expr.clone()
-                    } else {
-                        undefined(DUMMY_SP)
-                    };
-
-                    match param {
-                        Pat::Ident(param) => {
-                            inline_map.insert(param.id.to_id(), arg_val);
-                        }
-                        _ => {}
-                    }
-                }
-
-                self.inline_vars_in_node(&mut f.body, inline_map);
 
                 match &mut f.body {
                     BlockStmtOrExpr::BlockStmt(_) => {
@@ -330,17 +365,74 @@ impl Optimizer<'_> {
                     }
                     BlockStmtOrExpr::Expr(body) => {
                         self.changed = true;
-                        log::trace!("inline: Inlining a call to an arrow function");
+
+                        {
+                            let vars = f
+                                .params
+                                .iter()
+                                .cloned()
+                                .map(|name| VarDeclarator {
+                                    span: DUMMY_SP.apply_mark(self.marks.non_top_level),
+                                    name,
+                                    init: Default::default(),
+                                    definite: Default::default(),
+                                })
+                                .collect::<Vec<_>>();
+
+                            if !vars.is_empty() {
+                                self.prepend_stmts.push(Stmt::Decl(Decl::Var(VarDecl {
+                                    span: DUMMY_SP,
+                                    kind: VarDeclKind::Var,
+                                    declare: Default::default(),
+                                    decls: vars,
+                                })));
+                            }
+                        }
+
+                        let mut exprs = vec![];
+                        exprs.push(Box::new(make_number(DUMMY_SP, 0.0)));
+                        for (idx, param) in f.params.iter().enumerate() {
+                            if let Some(arg) = call.args.get_mut(idx) {
+                                exprs.push(Box::new(Expr::Assign(AssignExpr {
+                                    span: DUMMY_SP.apply_mark(self.marks.non_top_level),
+                                    op: op!("="),
+                                    left: PatOrExpr::Pat(Box::new(param.clone())),
+                                    right: arg.expr.take(),
+                                })));
+                            }
+                        }
+
+                        if call.args.len() > f.params.len() {
+                            for arg in &mut call.args[f.params.len()..] {
+                                exprs.push(arg.expr.take());
+                            }
+                        }
+                        exprs.push(body.take());
+
+                        log::debug!("inline: Inlining a call to an arrow function");
                         *e = Expr::Seq(SeqExpr {
                             span: DUMMY_SP,
-                            exprs: vec![Box::new(make_number(DUMMY_SP, 0.0)), body.take()],
+                            exprs,
                         });
                         return;
                     }
                 }
             }
             Expr::Fn(f) => {
+                if self.ctx.in_top_level() && !self.ctx.in_call_arg && self.options.negate_iife {
+                    let body = f.function.body.as_ref().unwrap();
+                    let has_decl = body.stmts.iter().any(|stmt| match stmt {
+                        Stmt::Decl(..) => true,
+                        _ => false,
+                    });
+                    if has_decl {
+                        log::trace!("iife: [x] Found decl");
+                        return;
+                    }
+                }
+
                 if f.function.is_generator {
+                    log::trace!("iife: [x] Cannot inline generator");
                     return;
                 }
 
@@ -349,17 +441,29 @@ impl Optimizer<'_> {
                     Pat::Object(..) | Pat::Array(..) | Pat::Assign(..) | Pat::Rest(..) => true,
                     _ => false,
                 }) {
+                    log::trace!("iife: [x] Found complex pattern");
                     return;
                 }
 
                 if let Some(i) = &f.ident {
                     if idents_used_by(&f.function.body).contains(&i.to_id()) {
+                        log::trace!("iife: [x] Recursive?");
                         return;
                     }
                 }
 
-                if is_param_used_by_body(&f.function.params, &f.function.body) {
+                for arg in &call.args {
-                    return;
+                    if arg.spread.is_some() {
+                        log::trace!("iife: [x] Found spread argument");
+                        return;
+                    }
+                    match &*arg.expr {
+                        Expr::Fn(..) | Expr::Arrow(..) => {
+                            log::trace!("iife: [x] Found callable argument");
+                            return;
+                        }
+                        _ => {}
+                    }
                 }
 
                 let body = f.function.body.as_mut().unwrap();
@@ -368,10 +472,22 @@ impl Optimizer<'_> {
                     return;
                 }
 
-                let new = self.inline_fn_like(body);
+                let param_ids = f
+                    .function
+                    .params
+                    .iter()
+                    .map(|p| p.pat.clone().ident().unwrap().id)
+                    .collect::<Vec<_>>();
+
+                if !self.can_inline_fn_like(&param_ids, body) {
+                    log::trace!("iife: [x] Body is not inliable");
+                    return;
+                }
+
+                let new = self.inline_fn_like(&param_ids, body, &mut call.args);
                 if let Some(new) = new {
                     self.changed = true;
-                    log::trace!("inline: Inlining a function call");
+                    log::debug!("inline: Inlining a function call");
 
                     *e = new;
                 }
@@ -382,11 +498,39 @@ impl Optimizer<'_> {
         }
     }
 
-    fn inline_fn_like(&mut self, body: &mut BlockStmt) -> Option<Expr> {
+    fn can_inline_fn_like(&self, param_ids: &[Ident], body: &BlockStmt) -> bool {
         if !body.stmts.iter().all(|stmt| match stmt {
-            Stmt::Expr(e) if e.expr.is_await_expr() => false,
+            Stmt::Decl(Decl::Var(VarDecl {
+                kind: VarDeclKind::Var | VarDeclKind::Let,
+                decls,
+                ..
+            })) => {
+                if decls.iter().any(|decl| match decl.name {
+                    Pat::Ident(..) => false,
+                    _ => true,
+                }) {
+                    return false;
+                }
+
+                if self.ctx.executed_multiple_time {
+                    return false;
+                }
+
+                true
+            }
+
+            Stmt::Expr(e) => match &*e.expr {
+                Expr::Await(..) => false,
+
+                // TODO: Check if paramter is used and inline if call is not related to parameters.
+                Expr::Call(e) => {
+                    let used = idents_used_by(e);
+                    param_ids.iter().all(|param| !used.contains(&param.to_id()))
+                }
+
+                _ => true,
+            },
 
-            Stmt::Expr(..) => true,
             Stmt::Return(ReturnStmt { arg, .. }) => match arg.as_deref() {
                 Some(Expr::Await(..)) => false,
 
@@ -401,12 +545,92 @@ impl Optimizer<'_> {
             },
             _ => false,
         }) {
+            return false;
+        }
+
+        if idents_used_by(&*body)
+            .iter()
+            .any(|v| v.0 == js_word!("arguments"))
+        {
+            return false;
+        }
+
+        true
+    }
+
+    fn inline_fn_like(
+        &mut self,
+        params: &[Ident],
+        body: &mut BlockStmt,
+        args: &mut [ExprOrSpread],
+    ) -> Option<Expr> {
+        if !self.can_inline_fn_like(&params, &*body) {
             return None;
         }
 
+        self.changed = true;
+        log::debug!("inline: Inling an iife");
+
         let mut exprs = vec![];
-        for stmt in body.stmts.take() {
+
+        {
+            let vars = params
+                .iter()
+                .cloned()
+                .map(BindingIdent::from)
+                .map(Pat::Ident)
+                .map(|name| VarDeclarator {
+                    span: DUMMY_SP.apply_mark(self.marks.non_top_level),
+                    name,
+                    init: Default::default(),
+                    definite: Default::default(),
+                })
+                .collect::<Vec<_>>();
+
+            if !vars.is_empty() {
+                self.prepend_stmts.push(Stmt::Decl(Decl::Var(VarDecl {
+                    span: DUMMY_SP,
+                    kind: VarDeclKind::Var,
+                    declare: Default::default(),
+                    decls: vars,
+                })));
+            }
+        }
+
+        for (idx, param) in params.iter().enumerate() {
+            if let Some(arg) = args.get_mut(idx) {
+                exprs.push(Box::new(Expr::Assign(AssignExpr {
+                    span: DUMMY_SP.apply_mark(self.marks.non_top_level),
+                    op: op!("="),
+                    left: PatOrExpr::Pat(Box::new(Pat::Ident(param.clone().into()))),
+                    right: arg.expr.take(),
+                })));
+            }
+        }
+
+        if args.len() > params.len() {
+            for arg in &mut args[params.len()..] {
+                exprs.push(arg.expr.take());
+            }
+        }
+
+        for mut stmt in body.stmts.take() {
             match stmt {
+                Stmt::Decl(Decl::Var(ref mut var)) => {
+                    for decl in &mut var.decls {
+                        if decl.init.is_some() {
+                            exprs.push(Box::new(Expr::Assign(AssignExpr {
+                                span: DUMMY_SP.apply_mark(self.marks.non_top_level),
+                                op: op!("="),
+                                left: PatOrExpr::Pat(Box::new(decl.name.clone())),
+                                right: decl.init.take().unwrap(),
+                            })))
+                        }
+                    }
+
+                    self.prepend_stmts.push(stmt);
+                }
+
                 Stmt::Expr(stmt) => {
                     exprs.push(stmt.expr);
                 }
@@ -513,29 +737,3 @@ impl Optimizer<'_> {
         }
     }
 }
-
-// We can't remove a function call if a parameter is declared by function and
-// the body of the function uses it.
-fn is_param_used_by_body<P, B>(params: &P, body: &B) -> bool
-where
-    P: for<'any> VisitWith<DestructuringFinder<'any, Id>>,
-    B: VisitWith<IdentUsageCollector>,
-{
-    let declared: Vec<Id> = find_ids(params);
-
-    let used = idents_used_by(body);
-
-    for id in declared {
-        if used.contains(&id) {
-            return true;
-        }
-    }
-
-    for (sym, _) in used {
-        if sym == js_word!("arguments") {
-            return true;
-        }
-    }
-
-    false
-}

ecmascript/minifier/src/compress/optimize/inline.rs

@@ -1,9 +1,13 @@
 use crate::compress::optimize::util::class_has_side_effect;
 use crate::compress::optimize::util::is_valid_for_lhs;
+use crate::debug::dump;
+use crate::util::has_mark;
+use crate::util::idents_used_by;
 
 use super::Optimizer;
 use swc_atoms::js_word;
 use swc_common::Spanned;
+use swc_common::DUMMY_SP;
 use swc_ecma_ast::*;
 use swc_ecma_transforms_base::ext::MapWithMut;
 use swc_ecma_utils::ident::IdentLike;
@@ -21,9 +25,18 @@ impl Optimizer<'_> {
             None => return,
         };
 
-        let should_preserve = (!self.options.top_level() && self.options.top_retain.is_empty())
+        let should_preserve = !has_mark(var.span, self.marks.non_top_level)
+            && (!self.options.top_level() && self.options.top_retain.is_empty())
             && self.ctx.in_top_level();
 
+        if cfg!(feature = "debug") {
+            log::trace!(
+                "inline: store_var_for_inining({}, should_preserve = {:?})",
+                dump(&var.name),
+                should_preserve
+            );
+        }
+
         if self
             .data
             .as_ref()
@@ -57,13 +70,34 @@ impl Optimizer<'_> {
                     }
 
                     if should_preserve && usage.var_kind != Some(VarDeclKind::Const) {
+                        if cfg!(feature = "debug") {
+                            log::trace!(
+                                "inline: Preserving non-const variable `{}` because it's top-level",
+                                dump(&var.name)
+                            );
+                        }
                         return;
                     }
 
                     if usage.cond_init || usage.used_above_decl {
+                        if cfg!(feature = "debug") {
+                            log::trace!("inline: [x] It's cond init or used before decl",);
+                        }
                         return;
                     }
 
+                    if !usage.is_fn_local {
+                        match &**init {
+                            Expr::Lit(..) => {}
+                            _ => {
+                                if cfg!(feature = "debug") {
+                                    log::trace!("inline: [x] It's not fn-local");
+                                }
+                                return;
+                            }
+                        }
+                    }
+
                     if !usage.reassigned {
                         match &**init {
                             Expr::Fn(..) | Expr::Arrow(..) => {
@@ -95,14 +129,12 @@ impl Optimizer<'_> {
                         && (!usage.mutated || (usage.assign_count == 0 && !usage.reassigned))
                         && match &**init {
                             Expr::Lit(lit) => match lit {
-                                Lit::Str(_)
+                                Lit::Str(_) => true,
-                                | Lit::Bool(_)
+                                Lit::Bool(_) | Lit::Null(_) | Lit::Num(_) | Lit::BigInt(_) => true,
-                                | Lit::Null(_)
-                                | Lit::Num(_)
-                                | Lit::BigInt(_) => true,
                                 Lit::Regex(_) => self.options.unsafe_regexp,
                                 _ => false,
                             },
+                            Expr::This(..) => usage.is_fn_local,
                             Expr::Arrow(arr) => is_arrow_simple_enough(arr),
                             _ => false,
                         }
@@ -114,7 +146,7 @@ impl Optimizer<'_> {
                                 _ => true,
                             }
                         {
-                            log::trace!(
+                            log::debug!(
                                 "inline: Decided to inline '{}{:?}' because it's simple",
                                 i.id.sym,
                                 i.id.span.ctxt
@@ -122,7 +154,7 @@ impl Optimizer<'_> {
 
                             self.lits.insert(i.to_id(), init.take());
                         } else {
-                            log::trace!(
+                            log::debug!(
                                 "inline: Decided to copy '{}{:?}' because it's simple",
                                 i.id.sym,
                                 i.id.span.ctxt
@@ -133,6 +165,13 @@ impl Optimizer<'_> {
                         return;
                     }
 
+                    if self.ctx.inline_as_assignment {
+                        if cfg!(feature = "debug") {
+                            log::trace!("inline: [x] inline_as_assignment is true");
+                        }
+                        return;
+                    }
+
                     // Single use => inlined
                     if is_inline_enabled
                         && !should_preserve
@@ -158,7 +197,11 @@ impl Optimizer<'_> {
                             _ => {}
                         }
                         match &**init {
-                            Expr::Lit(Lit::Regex(..)) => return,
+                            Expr::Lit(Lit::Regex(..)) => {
+                                if !usage.is_fn_local || usage.used_in_loop {
+                                    return;
+                                }
+                            }
 
                             Expr::This(..) => {
                                 // Don't inline this if it passes function boundaries.
@@ -170,17 +213,20 @@ impl Optimizer<'_> {
                             _ => {}
                         }
 
-                        if init.may_have_side_effects() {
+                        if usage.used_in_loop {
-                            if !self
+                            match &**init {
-                                .vars_accessible_without_side_effect
+                                Expr::Lit(..) | Expr::Ident(..) | Expr::Fn(..) => {}
-                                .contains(&i.to_id())
+                                _ => {
-                            {
+                                    return;
-                                // TODO: Inline partially
+                                }
-                                return;
                             }
                         }
 
-                        log::trace!(
+                        if init.may_have_side_effects() {
+                            return;
+                        }
+
+                        log::debug!(
                             "inline: Decided to inline '{}{:?}' because it's used only once",
                             i.id.sym,
                             i.id.span.ctxt
@@ -210,6 +256,10 @@ impl Optimizer<'_> {
                     _ => {}
                 },
 
+                Stmt::Try(TryStmt { block, .. }) => {
+                    return self.is_fn_body_simple_enough_to_inline(block)
+                }
+
                 _ => {}
             }
         }
@@ -234,7 +284,7 @@ impl Optimizer<'_> {
             .and_then(|data| data.vars.get(&i.to_id()))
         {
             if !usage.reassigned {
-                log::trace!("typeofs: Storing typeof `{}{:?}`", i.sym, i.span.ctxt);
+                log::debug!("typeofs: Storing typeof `{}{:?}`", i.sym, i.span.ctxt);
                 match &*decl {
                     Decl::Fn(..) => {
                         self.typeofs.insert(i.to_id(), js_word!("function"));
@@ -286,6 +336,10 @@ impl Optimizer<'_> {
             return;
         }
 
+        if self.ctx.inline_as_assignment {
+            return;
+        }
+
         if let Some(usage) = self
             .data
             .as_ref()
@@ -295,7 +349,7 @@ impl Optimizer<'_> {
                 return;
             }
 
-            if usage.reassigned {
+            if usage.reassigned || usage.inline_prevented {
                 return;
             }
 
@@ -305,14 +359,14 @@ impl Optimizer<'_> {
                     match &f.function.body {
                         Some(body) => {
                             if self.is_fn_body_simple_enough_to_inline(body) {
-                                log::trace!(
+                                log::debug!(
                                     "inline: Decided to inline function '{}{:?}' as it's very \
                                      simple",
                                     f.ident.sym,
                                     f.ident.span.ctxt
                                 );
 
-                                self.lits.insert(
+                                self.vars_for_inlining.insert(
                                     i.to_id(),
                                     match decl {
                                         Decl::Fn(f) => Box::new(Expr::Fn(FnExpr {
@@ -351,14 +405,14 @@ impl Optimizer<'_> {
                 self.changed = true;
                 match &decl {
                     Decl::Class(c) => {
-                        log::trace!(
+                        log::debug!(
                             "inline: Decided to inline class '{}{:?}' as it's used only once",
                             c.ident.sym,
                             c.ident.span.ctxt
                         );
                     }
                     Decl::Fn(f) => {
-                        log::trace!(
+                        log::debug!(
                             "inline: Decided to inline function '{}{:?}' as it's used only once",
                             f.ident.sym,
                             f.ident.span.ctxt
@@ -366,6 +420,7 @@ impl Optimizer<'_> {
                     }
                     _ => {}
                 }
+
                 self.vars_for_inlining.insert(
                     i.to_id(),
                     match decl.take() {
@@ -399,33 +454,92 @@ impl Optimizer<'_> {
                     return;
                 }
                 //
-                if let Some(value) = self.lits.get(&i.to_id()).cloned() {
+                if let Some(value) = self
+                    .lits
+                    .get(&i.to_id())
+                    .and_then(|v| {
+                        // Prevent infinite recursion.
+                        let ids = idents_used_by(&**v);
+                        if ids.contains(&i.to_id()) {
+                            None
+                        } else {
+                            Some(v)
+                        }
+                    })
+                    .cloned()
+                {
                     match &*value {
                         Expr::Lit(Lit::Num(..)) => {
                             if self.ctx.in_lhs_of_assign {
                                 return;
                             }
                         }
+                        Expr::Member(..) => {
+                            if self.ctx.executed_multiple_time {
+                                return;
+                            }
+                        }
                         _ => {}
                     }
 
                     self.changed = true;
-                    log::trace!("inline: Replacing a variable with cheap expression");
+                    log::debug!("inline: Replacing a variable with cheap expression");
 
                     *e = *value;
-                } else if let Some(value) = self.vars_for_inlining.get(&i.to_id()) {
+                    return;
+                }
+
+                if let Some(value) = self.vars_for_inlining.get(&i.to_id()) {
                     if self.ctx.is_exact_lhs_of_assign && !is_valid_for_lhs(&value) {
                         return;
                     }
 
+                    match &**value {
+                        Expr::Member(..) => {
+                            if self.ctx.executed_multiple_time {
+                                return;
+                            }
+                        }
+                        _ => {}
+                    }
+                }
+
+                if self.ctx.inline_as_assignment {
+                    if let Some(value) = self.vars_for_inlining.remove(&i.to_id()) {
+                        self.changed = true;
+                        log::debug!(
+                            "inline: Inlining '{}{:?}' using assignment",
+                            i.sym,
+                            i.span.ctxt
+                        );
+
+                        *e = Expr::Assign(AssignExpr {
+                            span: DUMMY_SP,
+                            op: op!("="),
+                            left: PatOrExpr::Pat(Box::new(Pat::Ident(i.clone().into()))),
+                            right: value,
+                        });
+
+                        if cfg!(feature = "debug") {
+                            log::trace!("inline: [Change] {}", dump(&*e))
+                        }
+                        return;
+                    }
+                }
+
+                if let Some(value) = self.vars_for_inlining.get(&i.to_id()) {
                     self.changed = true;
-                    log::trace!(
+                    log::debug!(
                         "inline: Replacing '{}{:?}' with an expression",
                         i.sym,
                         i.span.ctxt
                     );
 
                     *e = *value.clone();
+
+                    if cfg!(feature = "debug") {
+                        log::trace!("inline: [Change] {}", dump(&*e))
+                    }
                 }
             }
             _ => {}

ecmascript/minifier/src/compress/optimize/join_vars.rs

@@ -46,7 +46,7 @@ impl Optimizer<'_> {
             }
         }
 
-        log::trace!("join_vars: Joining variables");
+        log::debug!("join_vars: Joining variables");
         self.changed = true;
 
         let mut cur: Option<VarDecl> = None;

ecmascript/minifier/src/compress/optimize/loops.rs

@@ -1,5 +1,6 @@
 use crate::compress::optimize::unused::UnreachableHandler;
 use crate::compress::optimize::Optimizer;
+use swc_common::Spanned;
 use swc_common::DUMMY_SP;
 use swc_ecma_ast::*;
 use swc_ecma_transforms_base::ext::MapWithMut;
@@ -19,7 +20,7 @@ impl Optimizer<'_> {
         match s {
             Stmt::While(stmt) => {
                 self.changed = true;
-                log::trace!("loops: Converting a while loop to a for loop");
+                log::debug!("loops: Converting a while loop to a for loop");
                 *s = Stmt::For(ForStmt {
                     span: stmt.span,
                     init: None,
@@ -32,7 +33,7 @@ impl Optimizer<'_> {
                 let val = stmt.test.as_pure_bool();
                 if let Known(true) = val {
                     self.changed = true;
-                    log::trace!("loops: Converting an always-true do-while loop to a for loop");
+                    log::debug!("loops: Converting an always-true do-while loop to a for loop");
 
                     *s = Stmt::For(ForStmt {
                         span: stmt.span,
@@ -79,7 +80,7 @@ impl Optimizer<'_> {
         }
 
         self.changed = true;
-        log::trace!("loops: Removing a for loop with instant break");
+        log::debug!("loops: Removing a for loop with instant break");
         self.prepend_stmts
             .extend(f.init.take().map(|init| match init {
                 VarDeclOrExpr::VarDecl(var) => Stmt::Decl(Decl::Var(var)),
@@ -97,6 +98,70 @@ impl Optimizer<'_> {
         *s = Stmt::Empty(EmptyStmt { span: DUMMY_SP })
     }
 
+    /// # Input
+    ///
+    /// ```js
+    /// for(; size--;)
+    ///     if (!(result = eq(a[size], b[size], aStack, bStack)))
+    ///         break;
+    /// ```
+    ///
+    ///
+    /// # Output
+    ///
+    /// ```js
+    /// for (; size-- && (result = eq(a[size], b[size], aStack, bStack)););
+    /// ```
+    pub(super) fn merge_for_if_break(&mut self, s: &mut ForStmt) {
+        match &mut *s.body {
+            Stmt::If(IfStmt {
+                test,
+                cons,
+                alt: None,
+                ..
+            }) => {
+                match &**cons {
+                    Stmt::Break(BreakStmt { label: None, .. }) => {
+                        // We only care about instant breaks.
+                        //
+                        // Note: As the minifier of swc is very fast, we don't
+                        // care about block statements with a single break as a
+                        // body.
+                        //
+                        // If it's optimizable, other pass for if statements
+                        // will remove block and with the next pass we can apply
+                        // this pass.
+                        self.changed = true;
+                        log::debug!("loops: Compressing for-if-break into a for statement");
+
+                        // We negate because this `test` is used as a condition for `break`.
+                        self.negate(test);
+
+                        match s.test.take() {
+                            Some(left) => {
+                                s.test = Some(Box::new(Expr::Bin(BinExpr {
+                                    span: s.test.span(),
+                                    op: op!("&&"),
+                                    left,
+                                    right: test.take(),
+                                })));
+                            }
+                            None => {
+                                s.test = Some(test.take());
+                            }
+                        }
+
+                        // Remove body
+                        s.body.take();
+                    }
+                    _ => {}
+                }
+            }
+
+            _ => {}
+        }
+    }
+
     ///
     /// - `while(false) { var a; foo() }` => `var a;`
     pub(super) fn optiimze_loops_if_cond_is_false(&mut self, stmt: &mut Stmt) {
@@ -112,7 +177,7 @@ impl Optimizer<'_> {
                         let changed = UnreachableHandler::preserve_vars(stmt);
                         self.changed |= changed;
                         if changed {
-                            log::trace!(
+                            log::debug!(
                                 "loops: Removing unreachable while statement without side effects"
                             );
                         }
@@ -120,7 +185,7 @@ impl Optimizer<'_> {
                         let changed = UnreachableHandler::preserve_vars(&mut w.body);
                         self.changed |= changed;
                         if changed {
-                            log::trace!("loops: Removing unreachable body of a while statement");
+                            log::debug!("loops: Removing unreachable body of a while statement");
                         }
                     }
                 }
@@ -132,7 +197,7 @@ impl Optimizer<'_> {
                         let changed = UnreachableHandler::preserve_vars(&mut f.body);
                         self.changed |= changed;
                         if changed {
-                            log::trace!("loops: Removing unreachable body of a for statement");
+                            log::debug!("loops: Removing unreachable body of a for statement");
                         }
                         self.changed |= f.init.is_some() | f.update.is_some();
 
@@ -154,7 +219,7 @@ impl Optimizer<'_> {
                     } else if let Known(true) = val {
                         if purity.is_pure() {
                             self.changed = true;
-                            log::trace!(
+                            log::debug!(
                                 "loops: Remving `test` part of a for stmt as it's always true"
                             );
                             f.test = None;
@@ -190,7 +255,7 @@ impl Optimizer<'_> {
                     } else {
                         s.init = None;
                         self.changed = true;
-                        log::trace!(
+                        log::debug!(
                             "loops: Removed side-effect-free expressions in `init` of a for stmt"
                         );
                     }

ecmascript/minifier/src/compress/optimize/misc.rs

@@ -0,0 +1,38 @@
+use super::Optimizer;
+use swc_ecma_ast::*;
+use unicode_xid::UnicodeXID;
+
+impl Optimizer<'_> {
+    pub(super) fn optimize_prop_name(&mut self, name: &mut PropName) {
+        match name {
+            PropName::Str(s) => {
+                if s.value.is_reserved() || s.value.is_reserved_in_es3() {
+                    return;
+                }
+
+                if s.value.starts_with(|c: char| c.is_xid_start())
+                    && s.value.chars().all(|c: char| c.is_xid_continue())
+                    && !s.value.contains("𝒶")
+                {
+                    self.changed = true;
+                    log::debug!("misc: Optimizing string property name");
+                    *name = PropName::Ident(Ident {
+                        span: s.span,
+                        sym: s.value.clone(),
+                        optional: false,
+                    });
+                    return;
+                }
+            }
+            _ => {}
+        }
+    }
+
+    pub(super) fn remove_useless_return(&mut self, stmts: &mut Vec<Stmt>) {
+        if let Some(Stmt::Return(ReturnStmt { arg: None, .. })) = stmts.last() {
+            self.changed = true;
+            log::debug!("misc: Removing useless return");
+            stmts.pop();
+        }
+    }
+}

ecmascript/minifier/src/compress/optimize/numbers.rs

@@ -9,7 +9,7 @@ impl Optimizer<'_> {
                 let value = if value.is_empty() { 0f64 } else { 1f64 };
 
                 self.changed = true;
-                log::trace!("numbers: Converting a string literal to {:?}", value);
+                log::debug!("numbers: Converting a string literal to {:?}", value);
                 *e = Expr::Lit(Lit::Num(Number { span: *span, value }));
                 return;
             }
@@ -37,7 +37,7 @@ impl Optimizer<'_> {
                         ..
                     }) => {
                         self.changed = true;
-                        log::trace!("numbers: Lifting `-`");
+                        log::debug!("numbers: Lifting `-`");
 
                         *e = Expr::Unary(UnaryExpr {
                             span: arg.span,
@@ -55,7 +55,7 @@ impl Optimizer<'_> {
                     Expr::Lit(Lit::Num(Number { span, value, .. })) => {
                         if value.is_sign_negative() {
                             self.changed = true;
-                            log::trace!("numbers: Lifting `-` in a literal");
+                            log::debug!("numbers: Lifting `-` in a literal");
 
                             *e = Expr::Unary(UnaryExpr {
                                 span: arg.span,

ecmascript/minifier/src/compress/optimize/ops.rs

@@ -1,4 +1,8 @@
 use super::Optimizer;
+use crate::compress::optimize::bools::is_ok_to_negate_for_cond;
+use crate::compress::optimize::bools::is_ok_to_negate_rhs;
+use crate::compress::optimize::is_pure_undefined;
+use crate::debug::dump;
 use crate::util::make_bool;
 use crate::util::ValueExt;
 use std::mem::swap;
@@ -74,7 +78,7 @@ impl Optimizer<'_> {
                     match (lt, rt) {
                         (Type::Undefined, Type::Null) | (Type::Null, Type::Undefined) => {
                             if op == op!("===") {
-                                log::trace!(
+                                log::debug!(
                                     "Reducing `!== null || !== undefined` check to `!= null`"
                                 );
                                 return Some(BinExpr {
@@ -84,7 +88,7 @@ impl Optimizer<'_> {
                                     right: Box::new(Expr::Lit(Lit::Null(Null { span: DUMMY_SP }))),
                                 });
                             } else {
-                                log::trace!(
+                                log::debug!(
                                     "Reducing `=== null || === undefined` check to `== null`"
                                 );
                                 return Some(BinExpr {
@@ -167,7 +171,7 @@ impl Optimizer<'_> {
         if e.op == op!("===") || e.op == op!("!==") {
             if (e.left.is_ident() || e.left.is_member()) && e.left.eq_ignore_span(&e.right) {
                 self.changed = true;
-                log::trace!("Reducing comparison of same variable ({})", e.op);
+                log::debug!("Reducing comparison of same variable ({})", e.op);
 
                 e.op = if e.op == op!("===") {
                     op!("==")
@@ -187,7 +191,7 @@ impl Optimizer<'_> {
                     if lt == rt {
                         e.op = op!("==");
                         self.changed = true;
-                        log::trace!("Reduced `===` to `==` because types of operands are identical")
+                        log::debug!("Reduced `===` to `==` because types of operands are identical")
                     }
                 }
             }
@@ -209,7 +213,7 @@ impl Optimizer<'_> {
 
                 let value = if n.op == op!("==") { l == r } else { l != r };
 
-                log::trace!("Optimizing: literal comparison => bool");
+                log::debug!("Optimizing: literal comparison => bool");
                 self.changed = true;
                 return Some(Expr::Lit(Lit::Bool(Bool {
                     span: n.span,
@@ -249,7 +253,7 @@ impl Optimizer<'_> {
                     | Expr::Bin(BinExpr { op: op!(">"), .. }) => {
                         if let Known(Type::Bool) = arg.get_type() {
                             self.changed = true;
-                            log::trace!("Optimizing: `!!expr` => `expr`");
+                            log::debug!("Optimizing: `!!expr` => `expr`");
                             *e = *arg.take();
                         }
 
@@ -278,9 +282,9 @@ impl Optimizer<'_> {
     ///
     /// TODO: Handle special cases like !1 or !0
     pub(super) fn negate(&mut self, e: &mut Expr) {
-        self.changed = true;
+        let start_str = dump(&*e);
-        let arg = Box::new(e.take());
 
+        self.changed = true;
         match e {
             Expr::Bin(bin @ BinExpr { op: op!("=="), .. })
             | Expr::Bin(bin @ BinExpr { op: op!("!="), .. })
@@ -304,15 +308,68 @@ impl Optimizer<'_> {
                     }
                 };
                 self.changed = true;
-                log::trace!("negate: binary");
+                log::debug!("negate: binary");
                 return;
             }
 
+            Expr::Bin(BinExpr {
+                left,
+                right,
+                op: op @ op!("&&"),
+                ..
+            }) if is_ok_to_negate_rhs(&right) => {
+                log::debug!("negate: a && b => !a || !b");
+
+                self.negate(&mut **left);
+                self.negate(&mut **right);
+                *op = op!("||");
+                return;
+            }
+
+            Expr::Bin(BinExpr {
+                left,
+                right,
+                op: op @ op!("||"),
+                ..
+            }) if is_ok_to_negate_rhs(&right) => {
+                log::debug!("negate: a || b => !a && !b");
+
+                self.negate(&mut **left);
+                self.negate(&mut **right);
+                *op = op!("&&");
+                return;
+            }
+
+            Expr::Cond(CondExpr { cons, alt, .. })
+                if is_ok_to_negate_for_cond(&cons) && is_ok_to_negate_for_cond(&alt) =>
+            {
+                log::debug!("negate: cond");
+
+                self.negate(&mut **cons);
+                self.negate(&mut **alt);
+                return;
+            }
+
+            Expr::Seq(SeqExpr { exprs, .. }) => {
+                if let Some(last) = exprs.last_mut() {
+                    log::debug!("negate: seq");
+
+                    self.negate(&mut **last);
+                    return;
+                }
+            }
+
+            _ => {}
+        }
+
+        let mut arg = Box::new(e.take());
+
+        match &mut *arg {
             Expr::Unary(UnaryExpr {
                 op: op!("!"), arg, ..
             }) => match &mut **arg {
                 Expr::Unary(UnaryExpr { op: op!("!"), .. }) => {
-                    log::trace!("negate: !!bool => !bool");
+                    log::debug!("negate: !!bool => !bool");
                     *e = *arg.take();
                     return;
                 }
@@ -321,22 +378,33 @@ impl Optimizer<'_> {
                     op: op!("instanceof"),
                     ..
                 }) => {
-                    log::trace!("negate: !bool => bool");
+                    log::debug!("negate: !bool => bool");
                     *e = *arg.take();
                     return;
                 }
-                _ => {}
+                _ => {
+                    if self.ctx.in_bool_ctx {
+                        log::debug!("negate: !expr => expr (in bool context)");
+                        *e = *arg.take();
+                        return;
+                    }
+                }
             },
+
             _ => {}
         }
 
-        log::trace!("negate: e => !e");
+        log::debug!("negate: e => !e");
 
         *e = Expr::Unary(UnaryExpr {
             span: DUMMY_SP,
             op: op!("!"),
             arg,
         });
+
+        if cfg!(feature = "debug") {
+            log::trace!("[Change] Negated `{}` as `{}`", start_str, dump(&*e));
+        }
     }
 
     pub(super) fn handle_negated_seq(&mut self, n: &mut Expr) {
@@ -352,7 +420,7 @@ impl Optimizer<'_> {
                         if exprs.is_empty() {
                             return;
                         }
-                        log::trace!("optimizing negated sequences");
+                        log::debug!("optimizing negated sequences");
 
                         {
                             let last = exprs.last_mut().unwrap();
@@ -427,24 +495,60 @@ impl Optimizer<'_> {
             _ => return,
         };
 
-        log::trace!("Compressing: `e = 3 & e` => `e &= 3`");
+        log::debug!("Compressing: `e = 3 & e` => `e &= 3`");
 
         self.changed = true;
         e.op = op;
         e.right = left.take();
     }
 
+    /// Rules:
+    ///  - `l > i` => `i < l`
     fn can_swap_bin_operands(&mut self, l: &Expr, r: &Expr, is_for_rel: bool) -> bool {
         match (l, r) {
-            (Expr::Ident(l), Expr::Ident(r)) => {
+            (Expr::Member(_), _) if is_for_rel => false,
-                self.options.comparisons && (is_for_rel || l.sym > r.sym)
+
+            (Expr::Update(..) | Expr::Assign(..), Expr::Lit(..)) if is_for_rel => false,
+
+            (
+                Expr::Member(..)
+                | Expr::Call(..)
+                | Expr::Assign(..)
+                | Expr::Update(..)
+                | Expr::Bin(BinExpr {
+                    op: op!("&&") | op!("||"),
+                    ..
+                }),
+                Expr::Lit(..),
+            ) => true,
+
+            (
+                Expr::Member(..) | Expr::Call(..) | Expr::Assign(..),
+                Expr::Unary(UnaryExpr {
+                    op: op!("!"), arg, ..
+                }),
+            ) if match &**arg {
+                Expr::Lit(..) => true,
+                _ => false,
+            } =>
+            {
+                true
             }
 
+            (Expr::Member(..) | Expr::Call(..) | Expr::Assign(..), r) if is_pure_undefined(r) => {
+                true
+            }
+
+            (Expr::Ident(..), Expr::Lit(..)) if is_for_rel => false,
+
+            (Expr::Ident(..), Expr::Ident(..)) => false,
+
             (Expr::Ident(..), Expr::Lit(..))
             | (
-                Expr::Ident(..),
+                Expr::Ident(..) | Expr::Member(..),
                 Expr::Unary(UnaryExpr {
-                    op: op!("void"), ..
+                    op: op!("void") | op!("!"),
+                    ..
                 }),
             )
             | (
@@ -479,7 +583,7 @@ impl Optimizer<'_> {
         }
 
         if self.can_swap_bin_operands(&left, &right, false) {
-            log::trace!("Swapping operands of binary exprssion");
+            log::debug!("Swapping operands of binary exprssion");
             swap(left, right);
             return true;
         }
@@ -494,7 +598,7 @@ impl Optimizer<'_> {
             | Expr::Bin(e @ BinExpr { op: op!("<"), .. }) => {
                 if self.options.comparisons && self.can_swap_bin_operands(&e.left, &e.right, true) {
                     self.changed = true;
-                    log::trace!("comparisons: Swapping operands of {}", e.op);
+                    log::debug!("comparisons: Swapping operands of {}", e.op);
 
                     e.op = if e.op == op!("<=") {
                         op!(">=")
@@ -568,13 +672,13 @@ impl Optimizer<'_> {
 
                 if rb {
                     self.changed = true;
-                    log::trace!("Optimizing: e && true => !!e");
+                    log::debug!("Optimizing: e && true => !!e");
 
                     self.negate_twice(&mut bin.left);
                     *e = *bin.left.take();
                 } else {
                     self.changed = true;
-                    log::trace!("Optimizing: e && false => e");
+                    log::debug!("Optimizing: e && false => e");
 
                     *e = *bin.left.take();
                 }
@@ -588,7 +692,7 @@ impl Optimizer<'_> {
 
                 if !rb {
                     self.changed = true;
-                    log::trace!("Optimizing: e || false => !!e");
+                    log::debug!("Optimizing: e || false => !!e");
 
                     self.negate_twice(&mut bin.left);
                     *e = *bin.left.take();
@@ -648,7 +752,7 @@ impl Optimizer<'_> {
 
         match l {
             Expr::Lit(Lit::Null(..)) => {
-                log::trace!("Removing null from lhs of ??");
+                log::debug!("Removing null from lhs of ??");
                 self.changed = true;
                 *e = r.take();
                 return;
@@ -658,7 +762,7 @@ impl Optimizer<'_> {
             | Expr::Lit(Lit::BigInt(..))
             | Expr::Lit(Lit::Bool(..))
             | Expr::Lit(Lit::Regex(..)) => {
-                log::trace!("Removing rhs of ?? as lhs cannot be null nor undefined");
+                log::debug!("Removing rhs of ?? as lhs cannot be null nor undefined");
                 self.changed = true;
                 *e = l.take();
                 return;
@@ -682,7 +786,7 @@ impl Optimizer<'_> {
             }) => match &**arg {
                 Expr::Ident(arg) => {
                     if let Some(value) = self.typeofs.get(&arg.to_id()).cloned() {
-                        log::trace!(
+                        log::debug!(
                             "Converting typeof of variable to literal as we know the value"
                         );
                         self.changed = true;
@@ -697,7 +801,7 @@ impl Optimizer<'_> {
                 }
 
                 Expr::Arrow(..) | Expr::Fn(..) => {
-                    log::trace!("Converting typeof to 'function' as we know the value");
+                    log::debug!("Converting typeof to 'function' as we know the value");
                     self.changed = true;
                     *e = Expr::Lit(Lit::Str(Str {
                         span: *span,
@@ -709,7 +813,7 @@ impl Optimizer<'_> {
                 }
 
                 Expr::Array(..) | Expr::Object(..) => {
-                    log::trace!("Converting typeof to 'object' as we know the value");
+                    log::debug!("Converting typeof to 'object' as we know the value");
                     self.changed = true;
                     *e = Expr::Lit(Lit::Str(Str {
                         span: *span,

ecmascript/minifier/src/compress/optimize/properties.rs

@@ -60,6 +60,10 @@ impl Optimizer<'_> {
             return;
         }
 
+        if self.ctx.is_callee {
+            return;
+        }
+
         if obj.props.iter().any(|prop| match prop {
             PropOrSpread::Spread(_) => false,
             PropOrSpread::Prop(p) => match &**p {
@@ -87,7 +91,7 @@ impl Optimizer<'_> {
                     Prop::Shorthand(_) => {}
                     Prop::KeyValue(p) => {
                         if prop_name_eq(&p.key, &key.sym) {
-                            log::trace!("properties: Inlining a key-value property `{}`", key.sym);
+                            log::debug!("properties: Inlining a key-value property `{}`", key.sym);
                             self.changed = true;
                             *e = *p.value.clone();
                             return;

ecmascript/minifier/src/compress/optimize/strings.rs

@@ -58,7 +58,7 @@ impl Optimizer<'_> {
                         match &*args[0].expr {
                             Expr::Lit(Lit::Str(..)) => {
                                 self.changed = true;
-                                log::trace!(
+                                log::debug!(
                                     "strings: Unsafely reduced `RegExp` call in a string context"
                                 );
 
@@ -87,7 +87,7 @@ impl Optimizer<'_> {
                     Expr::Lit(Lit::Str(..)) => {
                         *n = *e.expr.take();
                         self.changed = true;
-                        log::trace!("string: Removed a paren in a string context");
+                        log::debug!("string: Removed a paren in a string context");
                     }
                     _ => {}
                 }
@@ -101,7 +101,7 @@ impl Optimizer<'_> {
         let value = n.as_string();
         if let Known(value) = value {
             self.changed = true;
-            log::trace!(
+            log::debug!(
                 "strings: Converted an expression into a string literal (in string context)"
             );
             *n = Expr::Lit(Lit::Str(Str {
@@ -116,7 +116,7 @@ impl Optimizer<'_> {
         match n {
             Expr::Lit(Lit::Num(v)) => {
                 self.changed = true;
-                log::trace!(
+                log::debug!(
                     "strings: Converted a numeric literal ({}) into a string literal (in string \
                      context)",
                     v.value
@@ -136,7 +136,7 @@ impl Optimizer<'_> {
                     return;
                 }
                 self.changed = true;
-                log::trace!(
+                log::debug!(
                     "strings: Converted a regex (/{}/{}) into a string literal (in string context)",
                     v.exp,
                     v.flags
@@ -163,7 +163,7 @@ impl Optimizer<'_> {
                     .unwrap_or(false)
                 {
                     self.changed = true;
-                    log::trace!(
+                    log::debug!(
                         "strings: Converting a reference ({}{:?}) into `undefined` (in string \
                          context)",
                         i.sym,
@@ -274,7 +274,7 @@ impl Optimizer<'_> {
                 if let Some(l_last) = l.quasis.last_mut() {
                     self.changed = true;
 
-                    log::trace!(
+                    log::debug!(
                         "template: Concatted a string (`{}`) on rhs of `+` to a template literal",
                         rs.value
                     );
@@ -294,7 +294,7 @@ impl Optimizer<'_> {
                 if let Some(r_first) = r.quasis.first_mut() {
                     self.changed = true;
 
-                    log::trace!(
+                    log::debug!(
                         "template: Prepended a string (`{}`) on lhs of `+` to a template literal",
                         ls.value
                     );
@@ -332,7 +332,7 @@ impl Optimizer<'_> {
 
                 debug_assert!(l.quasis.len() == l.exprs.len() + 1, "{:?} is invalid", l);
                 self.changed = true;
-                log::trace!("strings: Merged to template literals");
+                log::debug!("strings: Merged to template literals");
             }
 
             _ => {}
@@ -365,7 +365,7 @@ impl Optimizer<'_> {
                                     let left_span = left.span;
 
                                     self.changed = true;
-                                    log::trace!(
+                                    log::debug!(
                                         "string: Concatting `{} + {}` to `{}`",
                                         second_str,
                                         third_str,
@@ -413,7 +413,7 @@ impl Optimizer<'_> {
                                 ..
                             })) => {
                                 self.changed = true;
-                                log::trace!(
+                                log::debug!(
                                     "string: Dropping empty string literal (in lhs) because it \
                                      does not changes type"
                                 );
@@ -430,7 +430,7 @@ impl Optimizer<'_> {
                                 ..
                             })) => {
                                 self.changed = true;
-                                log::trace!(
+                                log::debug!(
                                     "string: Dropping empty string literal (in rhs) because it \
                                      does not changes type"
                                 );

ecmascript/minifier/src/compress/optimize/switches.rs

@@ -1,3 +1,5 @@
+use std::mem::take;
+
 use super::Optimizer;
 use crate::util::ExprOptExt;
 use swc_common::EqIgnoreSpan;
@@ -5,7 +7,9 @@ use swc_common::DUMMY_SP;
 use swc_ecma_ast::*;
 use swc_ecma_transforms_base::ext::MapWithMut;
 use swc_ecma_utils::ident::IdentLike;
+use swc_ecma_utils::prepend;
 use swc_ecma_utils::ExprExt;
+use swc_ecma_utils::StmtExt;
 use swc_ecma_utils::Type;
 use swc_ecma_utils::Value::Known;
 use swc_ecma_visit::noop_visit_type;
@@ -45,6 +49,7 @@ impl Optimizer<'_> {
         });
 
         if let Some(case_idx) = matching_case {
+            let mut var_ids = vec![];
             let mut stmts = vec![];
 
             let should_preserve_switch = stmt.cases.iter().skip(case_idx).any(|case| {
@@ -60,9 +65,9 @@ impl Optimizer<'_> {
                     return;
                 }
 
-                log::trace!("switches: Removing unreachable cases from a constant switch");
+                log::debug!("switches: Removing unreachable cases from a constant switch");
             } else {
-                log::trace!("switches: Removing a constant switch");
+                log::debug!("switches: Removing a constant switch");
             }
 
             self.changed = true;
@@ -81,6 +86,21 @@ impl Optimizer<'_> {
                 }
             }
 
+            for case in &stmt.cases[..case_idx] {
+                for cons in &case.cons {
+                    var_ids.extend(
+                        cons.extract_var_ids()
+                            .into_iter()
+                            .map(|name| VarDeclarator {
+                                span: DUMMY_SP,
+                                name: Pat::Ident(name.into()),
+                                init: None,
+                                definite: Default::default(),
+                            }),
+                    );
+                }
+            }
+
             for case in stmt.cases.iter_mut().skip(case_idx) {
                 let mut found_break = false;
                 case.cons.retain(|stmt| match stmt {
@@ -110,6 +130,18 @@ impl Optimizer<'_> {
                 }
             }
 
+            if !var_ids.is_empty() {
+                prepend(
+                    &mut stmts,
+                    Stmt::Decl(Decl::Var(VarDecl {
+                        span: DUMMY_SP,
+                        kind: VarDeclKind::Var,
+                        declare: Default::default(),
+                        decls: take(&mut var_ids),
+                    })),
+                )
+            }
+
             let inner = if should_preserve_switch {
                 let mut cases = stmt.cases.take();
                 let case = SwitchCase {
@@ -193,7 +225,7 @@ impl Optimizer<'_> {
         if !preserve_cases {
             if let Some(last_non_empty) = last_non_empty {
                 if last_non_empty + 1 != cases.len() {
-                    log::trace!("switches: Removing empty cases at the end");
+                    log::debug!("switches: Removing empty cases at the end");
                     self.changed = true;
                     cases.drain(last_non_empty + 1..);
                 }
@@ -203,7 +235,7 @@ impl Optimizer<'_> {
         if let Some(last) = cases.last_mut() {
             match last.cons.last() {
                 Some(Stmt::Break(BreakStmt { label: None, .. })) => {
-                    log::trace!("switches: Removing `break` at the end");
+                    log::debug!("switches: Removing `break` at the end");
                     self.changed = true;
                     last.cons.pop();
                 }
@@ -215,12 +247,23 @@ impl Optimizer<'_> {
     /// If a case ends with break but content is same with the consequtive case
     /// except the break statement, we merge them.
     fn merge_cases_with_same_cons(&mut self, cases: &mut Vec<SwitchCase>) {
+        let stop_pos = cases.iter().position(|case| match case.test.as_deref() {
+            Some(Expr::Update(..)) => true,
+            _ => false,
+        });
+
         let mut found = None;
         'l: for (li, l) in cases.iter().enumerate().rev() {
             if l.cons.is_empty() {
                 continue;
             }
 
+            if let Some(stop_pos) = stop_pos {
+                if li > stop_pos {
+                    continue;
+                }
+            }
+
             if let Some(l_last) = l.cons.last() {
                 match l_last {
                     Stmt::Break(BreakStmt { label: None, .. }) => {}
@@ -253,7 +296,7 @@ impl Optimizer<'_> {
 
         if let Some(idx) = found {
             self.changed = true;
-            log::trace!("switches: Merging cases with same cons");
+            log::debug!("switches: Merging cases with same cons");
             cases[idx].cons.clear();
         }
     }

ecmascript/minifier/src/compress/optimize/unused.rs

@@ -1,19 +1,77 @@
-use crate::compress::optimize::util::class_has_side_effect;
-use crate::option::PureGetterOption;
-
 use super::Optimizer;
+use crate::compress::optimize::util::class_has_side_effect;
+use crate::debug::dump;
+use crate::option::PureGetterOption;
+use crate::util::has_mark;
 use swc_atoms::js_word;
+use swc_common::Span;
 use swc_common::DUMMY_SP;
 use swc_ecma_ast::*;
 use swc_ecma_transforms_base::ext::MapWithMut;
 use swc_ecma_utils::contains_ident_ref;
 use swc_ecma_utils::ident::IdentLike;
+use swc_ecma_utils::StmtLike;
 use swc_ecma_visit::noop_visit_mut_type;
 use swc_ecma_visit::VisitMut;
 use swc_ecma_visit::VisitMutWith;
 
 /// Methods related to the option `unused`.
 impl Optimizer<'_> {
+    pub(super) fn drop_useless_blocks<T>(&mut self, stmts: &mut Vec<T>)
+    where
+        T: StmtLike,
+    {
+        fn is_inliable(b: &BlockStmt) -> bool {
+            b.stmts.iter().all(|s| match s {
+                Stmt::Decl(Decl::Fn(FnDecl {
+                    ident:
+                        Ident {
+                            sym: js_word!("undefined"),
+                            ..
+                        },
+                    ..
+                })) => false,
+
+                Stmt::Decl(
+                    Decl::Var(VarDecl {
+                        kind: VarDeclKind::Var,
+                        ..
+                    })
+                    | Decl::Fn(..),
+                ) => true,
+                Stmt::Decl(..) => false,
+                _ => true,
+            })
+        }
+
+        if stmts.iter().all(|stmt| match stmt.as_stmt() {
+            Some(Stmt::Block(b)) if is_inliable(b) => false,
+            _ => true,
+        }) {
+            return;
+        }
+
+        self.changed = true;
+        log::debug!("Dropping useless block");
+
+        let mut new = vec![];
+        for stmt in stmts.take() {
+            match stmt.try_into_stmt() {
+                Ok(v) => match v {
+                    Stmt::Block(v) if is_inliable(&v) => {
+                        new.extend(v.stmts.into_iter().map(T::from_stmt));
+                    }
+                    _ => new.push(T::from_stmt(v)),
+                },
+                Err(v) => {
+                    new.push(v);
+                }
+            }
+        }
+
+        *stmts = new;
+    }
+
     pub(super) fn drop_unused_stmt_at_end_of_fn(&mut self, s: &mut Stmt) {
         match s {
             Stmt::Return(r) => match r.arg.as_deref_mut() {
@@ -22,7 +80,7 @@ impl Optimizer<'_> {
                     op: op!("void"),
                     arg,
                 })) => {
-                    log::trace!("unused: Removing `return void` in end of a function");
+                    log::debug!("unused: Removing `return void` in end of a function");
                     self.changed = true;
                     *s = Stmt::Expr(ExprStmt {
                         span: *span,
@@ -48,7 +106,7 @@ impl Optimizer<'_> {
                     ..
                 }) => {}
                 _ => {
-                    self.drop_unused_vars(&mut var.name, Some(init));
+                    self.drop_unused_vars(var.span, &mut var.name, Some(init));
 
                     if var.name.is_invalid() {
                         let side_effects = self.ignore_return_value(init);
@@ -62,7 +120,7 @@ impl Optimizer<'_> {
                 }
             },
             None => {
-                self.drop_unused_vars(&mut var.name, var.init.as_deref_mut());
+                self.drop_unused_vars(var.span, &mut var.name, var.init.as_deref_mut());
             }
         }
     }
@@ -87,30 +145,53 @@ impl Optimizer<'_> {
             return;
         }
 
-        self.take_pat_if_unused(pat, None)
+        self.take_pat_if_unused(DUMMY_SP, pat, None)
     }
 
-    pub(super) fn drop_unused_vars(&mut self, name: &mut Pat, init: Option<&mut Expr>) {
+    pub(super) fn drop_unused_vars(
-        if !self.options.unused || self.ctx.in_var_decl_of_for_in_or_of_loop || self.ctx.is_exported
+        &mut self,
-        {
+        var_declarator_span: Span,
-            return;
+        name: &mut Pat,
+        init: Option<&mut Expr>,
+    ) {
+        let has_mark = has_mark(var_declarator_span, self.marks.non_top_level);
+
+        if !has_mark {
+            if !self.options.unused
+                || self.ctx.in_var_decl_of_for_in_or_of_loop
+                || self.ctx.is_exported
+            {
+                return;
+            }
+        }
+
+        if cfg!(feature = "debug") {
+            log::trace!("unused: drop_unused_vars({})", dump(&*name));
         }
 
         // Top-level
-        match self.ctx.var_kind {
+        if !has_mark {
-            Some(VarDeclKind::Var) => {
+            match self.ctx.var_kind {
-                if (!self.options.top_level() && self.options.top_retain.is_empty())
+                Some(VarDeclKind::Var) => {
-                    && self.ctx.in_top_level()
+                    if (!self.options.top_level() && self.options.top_retain.is_empty())
-                {
+                        && self.ctx.in_top_level()
-                    return;
+                    {
+                        if cfg!(feature = "debug") {
+                            log::trace!(
+                                "unused: Preserving `var` `{}` because it's top-level",
+                                dump(&*name)
+                            );
+                        }
+                        return;
+                    }
                 }
-            }
+                Some(VarDeclKind::Let) | Some(VarDeclKind::Const) => {
-            Some(VarDeclKind::Let) | Some(VarDeclKind::Const) => {
+                    if !self.options.top_level() && self.ctx.is_top_level_for_block_level_vars() {
-                if !self.options.top_level() && self.ctx.is_top_level_for_block_level_vars() {
+                        return;
-                    return;
+                    }
                 }
+                None => {}
             }
-            None => {}
         }
 
         if let Some(scope) = self
@@ -127,12 +208,12 @@ impl Optimizer<'_> {
             return;
         }
 
-        self.take_pat_if_unused(name, init);
+        self.take_pat_if_unused(var_declarator_span, name, init);
     }
 
     pub(super) fn drop_unused_params(&mut self, params: &mut Vec<Param>) {
         for param in params.iter_mut().rev() {
-            self.take_pat_if_unused(&mut param.pat, None);
+            self.take_pat_if_unused(DUMMY_SP, &mut param.pat, None);
 
             if !param.pat.is_invalid() {
                 return;
@@ -140,7 +221,13 @@ impl Optimizer<'_> {
         }
     }
 
-    pub(super) fn take_pat_if_unused(&mut self, name: &mut Pat, mut init: Option<&mut Expr>) {
+    /// `parent_span` should be [Span] of [VarDeclarator] or [AssignExpr]
+    pub(super) fn take_pat_if_unused(
+        &mut self,
+        parent_span: Span,
+        name: &mut Pat,
+        mut init: Option<&mut Expr>,
+    ) {
         let had_value = init.is_some();
         let can_drop_children = had_value;
 
@@ -153,7 +240,9 @@ impl Optimizer<'_> {
 
         match name {
             Pat::Ident(i) => {
-                if self.options.top_retain.contains(&i.id.sym) {
+                if !has_mark(parent_span, self.marks.non_top_level)
+                    && self.options.top_retain.contains(&i.id.sym)
+                {
                     return;
                 }
 
@@ -165,7 +254,7 @@ impl Optimizer<'_> {
                     .unwrap_or(false)
                 {
                     self.changed = true;
-                    log::trace!(
+                    log::debug!(
                         "unused: Dropping a variable '{}{:?}' because it is not used",
                         i.id.sym,
                         i.id.span.ctxt
@@ -173,6 +262,10 @@ impl Optimizer<'_> {
                     // This will remove variable.
                     name.take();
                     return;
+                } else {
+                    if cfg!(feature = "debug") {
+                        log::trace!("unused: Cannot drop ({}) becaue it's used", dump(&*i));
+                    }
                 }
             }
 
@@ -188,7 +281,7 @@ impl Optimizer<'_> {
                                 .as_mut()
                                 .and_then(|expr| self.access_numeric_property(expr, idx));
 
-                            self.take_pat_if_unused(p, elem);
+                            self.take_pat_if_unused(parent_span, p, elem);
                         }
                         None => {}
                     }
@@ -224,7 +317,7 @@ impl Optimizer<'_> {
                                 continue;
                             }
 
-                            self.take_pat_if_unused(&mut p.value, prop);
+                            self.take_pat_if_unused(parent_span, &mut p.value, prop);
                         }
                         ObjectPatProp::Assign(_) => {}
                         ObjectPatProp::Rest(_) => {}
@@ -303,7 +396,7 @@ impl Optimizer<'_> {
                     .unwrap_or(false)
                 {
                     self.changed = true;
-                    log::trace!(
+                    log::debug!(
                         "unused: Dropping a decl '{}{:?}' because it is not used",
                         ident.sym,
                         ident.span.ctxt
@@ -327,7 +420,14 @@ impl Optimizer<'_> {
     }
 
     pub(super) fn drop_unused_assignments(&mut self, e: &mut Expr) {
-        if !self.options.unused {
+        let assign = match e {
+            Expr::Assign(e) => e,
+            _ => return,
+        };
+
+        let has_mark = has_mark(assign.span, self.marks.non_top_level);
+
+        if !has_mark && !self.options.unused {
             return;
         }
 
@@ -344,19 +444,36 @@ impl Optimizer<'_> {
             return;
         }
 
-        if (!self.options.top_level() && self.options.top_retain.is_empty())
+        if cfg!(feature = "debug") {
+            log::trace!(
+                "unused: drop_unused_assignments: Target: `{}`",
+                dump(&assign.left)
+            )
+        }
+
+        if !has_mark
+            && (!self.options.top_level() && self.options.top_retain.is_empty())
             && self.ctx.in_top_level()
         {
+            if cfg!(feature = "debug") {
+                log::trace!(
+                    "unused: Preserving assignment to `{}` because it's top-level",
+                    dump(&assign.left)
+                )
+            }
             return;
         }
 
-        let assign = match e {
-            Expr::Assign(e) => e,
-            _ => return,
-        };
-
         match &mut assign.left {
-            PatOrExpr::Expr(_) => return,
+            PatOrExpr::Expr(_) => {
+                if cfg!(feature = "debug") {
+                    log::trace!(
+                        "unused: Preserving assignment to `{}` because it's an expression",
+                        dump(&assign.left)
+                    )
+                }
+                return;
+            }
             PatOrExpr::Pat(left) => match &**left {
                 Pat::Ident(i) => {
                     if self.options.top_retain.contains(&i.id.sym) {
@@ -369,7 +486,7 @@ impl Optimizer<'_> {
                         .and_then(|data| data.vars.get(&i.to_id()))
                     {
                         if var.is_fn_local && var.usage_count == 0 {
-                            log::trace!(
+                            log::debug!(
                                 "unused: Dropping assignment to var '{}{:?}', which is never used",
                                 i.id.sym,
                                 i.id.span.ctxt
@@ -377,6 +494,14 @@ impl Optimizer<'_> {
                             self.changed = true;
                             *e = *assign.right.take();
                             return;
+                        } else {
+                            if cfg!(feature = "debug") {
+                                log::trace!(
+                                    "unused: Preserving assignment to `{}` because of usage: {:?}",
+                                    dump(&assign.left),
+                                    var
+                                )
+                            }
                         }
                     }
                 }
@@ -405,7 +530,7 @@ impl Optimizer<'_> {
 
                 if can_remove_ident {
                     self.changed = true;
-                    log::trace!("Removing ident of an class / function expression");
+                    log::debug!("Removing ident of an class / function expression");
                     *name = None;
                 }
             }
@@ -429,7 +554,7 @@ impl Optimizer<'_> {
                 }
 
                 self.changed = true;
-                log::trace!(
+                log::debug!(
                     "unused: Removing the name of a function expression because it's not used by \
                      it'"
                 );

ecmascript/minifier/src/compress/optimize/util.rs

@@ -12,6 +12,12 @@ use swc_ecma_utils::prop_name_eq;
 use swc_ecma_utils::ExprExt;
 
 impl<'b> Optimizer<'b> {
+    pub(super) fn line_col(&self, span: Span) -> String {
+        let loc = self.cm.lookup_char_pos(span.lo);
+
+        format!("{}:{}", loc.line, loc.col_display)
+    }
+
     pub(super) fn access_property<'e>(
         &mut self,
         expr: &'e mut Expr,
@@ -224,6 +230,40 @@ pub(crate) fn class_has_side_effect(c: &Class) -> bool {
     false
 }
 
+pub(crate) fn get_lhs_ident(e: &PatOrExpr) -> Option<&Ident> {
+    match e {
+        PatOrExpr::Expr(v) => match &**v {
+            Expr::Ident(i) => Some(i),
+            _ => None,
+        },
+        PatOrExpr::Pat(v) => match &**v {
+            Pat::Ident(i) => Some(&i.id),
+            Pat::Expr(v) => match &**v {
+                Expr::Ident(i) => Some(i),
+                _ => None,
+            },
+            _ => None,
+        },
+    }
+}
+
+pub(crate) fn get_lhs_ident_mut(e: &mut PatOrExpr) -> Option<&mut Ident> {
+    match e {
+        PatOrExpr::Expr(v) => match &mut **v {
+            Expr::Ident(i) => Some(i),
+            _ => None,
+        },
+        PatOrExpr::Pat(v) => match &mut **v {
+            Pat::Ident(i) => Some(&mut i.id),
+            Pat::Expr(v) => match &mut **v {
+                Expr::Ident(i) => Some(i),
+                _ => None,
+            },
+            _ => None,
+        },
+    }
+}
+
 pub(crate) fn is_valid_for_lhs(e: &Expr) -> bool {
     match e {
         Expr::Lit(..) => return false,

ecmascript/minifier/src/debug.rs

@@ -41,6 +41,10 @@ pub(crate) fn dump<N>(node: &N) -> String
 where
     N: swc_ecma_codegen::Node + Clone + VisitMutWith<DropSpan> + VisitMutWith<Debugger>,
 {
+    if !cfg!(feature = "debug") {
+        return String::new();
+    }
+
     let mut node = node.clone();
     node.visit_mut_with(&mut Debugger);
     node = drop_span(node);
@@ -109,5 +113,5 @@ pub(crate) fn invoke(module: &Module) {
         );
     }
 
-    log::debug!("[SWC_RUN]\n{}", String::from_utf8_lossy(&output.stdout))
+    log::info!("[SWC_RUN]\n{}", String::from_utf8_lossy(&output.stdout))
 }

ecmascript/minifier/src/lib.rs

@@ -14,6 +14,7 @@
 
 use crate::compress::compressor;
 use crate::hygiene::unique_marker;
+use crate::marks::Marks;
 use crate::option::ExtraOptions;
 use crate::option::MinifyOptions;
 use crate::pass::compute_char_freq::compute_char_freq;
@@ -23,9 +24,13 @@ use crate::pass::hygiene::hygiene_optimizer;
 pub use crate::pass::hygiene::optimize_hygiene;
 use crate::pass::mangle_names::name_mangler;
 use crate::pass::mangle_props::mangle_properties;
-use crate::pass::single::single_pass_optimizer;
+use crate::pass::precompress::precompress_optimizer;
 use analyzer::analyze;
+use pass::postcompress::postcompress_optimizer;
+use std::time::Instant;
 use swc_common::comments::Comments;
+use swc_common::sync::Lrc;
+use swc_common::SourceMap;
 use swc_ecma_ast::Module;
 use swc_ecma_visit::FoldWith;
 use swc_ecma_visit::VisitMutWith;
@@ -35,6 +40,7 @@ mod analyzer;
 mod compress;
 mod debug;
 mod hygiene;
+mod marks;
 pub mod option;
 mod pass;
 pub mod timing;
@@ -43,11 +49,15 @@ mod util;
 #[inline]
 pub fn optimize(
     mut m: Module,
+    cm: Lrc<SourceMap>,
     comments: Option<&dyn Comments>,
     mut timings: Option<&mut Timings>,
     options: &MinifyOptions,
     extra: &ExtraOptions,
 ) -> Module {
+    let marks = Marks::new();
+
+    let start = Instant::now();
     if let Some(defs) = options.compress.as_ref().map(|c| &c.global_defs) {
         // Apply global defs.
         //
@@ -60,10 +70,13 @@ pub fn optimize(
             m.visit_mut_with(&mut global_defs::globals_defs(defs, extra.top_level_mark));
         }
     }
+    log::info!("global_defs took {:?}", Instant::now() - start);
 
-    m.visit_mut_with(&mut single_pass_optimizer(
+    if let Some(options) = &options.compress {
-        options.compress.clone().unwrap_or_default(),
+        let start = Instant::now();
-    ));
+        m.visit_mut_with(&mut precompress_optimizer(options.clone()));
+        log::info!("precompress took {:?}", Instant::now() - start);
+    }
 
     m.visit_mut_with(&mut unique_marker());
 
@@ -95,8 +108,14 @@ pub fn optimize(
         t.section("compress");
     }
     if let Some(options) = &options.compress {
-        m = m.fold_with(&mut compressor(&options, comments));
+        let start = Instant::now();
+        m = m.fold_with(&mut compressor(cm.clone(), marks, &options, comments));
+        log::info!("compressor took {:?}", Instant::now() - start);
         // Again, we don't need to validate ast
+
+        let start = Instant::now();
+        m.visit_mut_with(&mut postcompress_optimizer(options));
+        log::info!("postcompressor took {:?}", Instant::now() - start);
     }
 
     if let Some(ref mut _t) = timings {

ecmascript/minifier/src/marks.rs

@@ -0,0 +1,18 @@
+use swc_common::Mark;
+
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct Marks {
+    /// [Mark] applied to non-top level varaibles which is injected while
+    /// inlining.
+    pub(crate) non_top_level: Mark,
+}
+
+impl Marks {
+    pub fn new() -> Marks {
+        fn m() -> Mark {
+            Mark::fresh(Mark::root())
+        }
+
+        Marks { non_top_level: m() }
+    }
+}

ecmascript/minifier/src/option/mod.rs

@@ -55,6 +55,9 @@ pub struct MangleOptions {
     #[serde(default, alias = "keep_fnames")]
     pub keep_fn_names: bool,
 
+    #[serde(default, alias = "keep_private_props")]
+    pub keep_private_props: bool,
+
     #[serde(default, alias = "ie8")]
     pub ie8: bool,
 
@@ -171,6 +174,7 @@ pub struct CompressOptions {
     #[serde(alias = "hoist_vars")]
     pub hoist_vars: bool,
 
+    /// No effect.
     #[serde(default)]
     #[serde(alias = "ie8")]
     pub ie8: bool,

ecmascript/minifier/src/pass/hygiene/analyzer.rs

@@ -40,6 +40,21 @@ impl HygieneAnalyzer<'_> {
 
         let ret = op(self);
 
+        let mut ids = vec![];
+        {
+            let scope = self.scope();
+            for (sym, ctxts) in &scope.declared_symbols {
+                if ctxts.len() == 1 {
+                    let id = (sym.clone(), *ctxts.iter().next().unwrap());
+                    ids.push(id)
+                }
+            }
+        }
+        for id in ids {
+            self.hygiene.preserved.remove(&id);
+            self.hygiene.modified.insert(id);
+        }
+
         self.cur_scope = old;
 
         ret

ecmascript/minifier/src/pass/hygiene/mod.rs

@@ -69,7 +69,7 @@ impl VisitMut for Optimizer {
     }
 
     fn visit_mut_module(&mut self, n: &mut Module) {
-        log::debug!("hygiene: Analyzing span hygiene");
+        log::info!("hygiene: Analyzing span hygiene");
         let start = Instant::now();
 
         let mut analyzer = HygieneAnalyzer {
@@ -82,12 +82,12 @@ impl VisitMut for Optimizer {
         self.hygiene = analyzer.hygiene;
 
         let end = Instant::now();
-        log::debug!("hygiene: Span hygiene analysis took {:?}", end - start);
+        log::info!("hygiene: Span hygiene analysis took {:?}", end - start);
         let start = end;
 
-        log::debug!("hygiene: Optimizing span hygiene");
+        log::info!("hygiene: Optimizing span hygiene");
         n.visit_mut_children_with(self);
         let end = Instant::now();
-        log::debug!("hygiene: Span hygiene optimiation took {:?}", end - start);
+        log::info!("hygiene: Span hygiene optimiation took {:?}", end - start);
     }
 }

ecmascript/minifier/src/pass/mangle_names/mod.rs

@@ -28,9 +28,12 @@ pub fn name_mangler(options: MangleOptions, _char_freq_info: CharFreqInfo) -> im
 struct Mangler {
     options: MangleOptions,
     n: usize,
+    private_n: usize,
+
     preserved: FxHashSet<Id>,
     preserved_symbols: FxHashSet<JsWord>,
     renamed: FxHashMap<Id, JsWord>,
+    renamed_private: FxHashMap<Id, JsWord>,
     data: Option<ProgramData>,
 }
 
@@ -65,6 +68,23 @@ impl Mangler {
             break;
         }
     }
+
+    fn rename_private(&mut self, private_name: &mut PrivateName) {
+        let id = private_name.id.to_id();
+
+        let new_sym = if let Some(cached) = self.renamed_private.get(&id) {
+            cached.clone()
+        } else {
+            let sym: JsWord = base54(self.private_n).into();
+            self.private_n += 1;
+
+            self.renamed_private.insert(id.clone(), sym.clone());
+
+            sym
+        };
+
+        private_name.id.sym = new_sym;
+    }
 }
 
 impl VisitMut for Mangler {
@@ -95,6 +115,12 @@ impl VisitMut for Mangler {
         }
     }
 
+    fn visit_mut_private_name(&mut self, private_name: &mut PrivateName) {
+        if !self.options.keep_private_props {
+            self.rename_private(private_name);
+        }
+    }
+
     fn visit_mut_fn_decl(&mut self, n: &mut FnDecl) {
         self.rename(&mut n.ident);
         n.function.visit_mut_with(self);

ecmascript/minifier/src/pass/mangle_props.rs

@@ -6,8 +6,8 @@ use once_cell::sync::Lazy;
 use std::collections::{HashMap, HashSet};
 use swc_atoms::JsWord;
 use swc_ecma_ast::{
-    CallExpr, Expr, ExprOrSuper, Ident, KeyValueProp, Lit, MemberExpr, Module, PrivateName, Prop,
+    CallExpr, Expr, ExprOrSuper, Ident, KeyValueProp, Lit, MemberExpr, Module, Prop, PropName, Str,
-    PropName, Str, StrKind,
+    StrKind,
 };
 use swc_ecma_utils::ident::IdentLike;
 use swc_ecma_visit::{VisitMut, VisitMutWith};
@@ -37,11 +37,9 @@ struct ManglePropertiesState {
 
     // Cache of already mangled names
     cache: HashMap<JsWord, JsWord>,
-    private_cache: HashMap<JsWord, JsWord>,
 
     // Numbers to pass to base54()
     n: usize,
-    private_n: usize,
 }
 
 impl ManglePropertiesState {
@@ -103,23 +101,6 @@ impl ManglePropertiesState {
             None
         }
     }
-
-    fn gen_private_name(&mut self, name: &JsWord) -> JsWord {
-        // Always mangleable
-        if let Some(cached) = self.private_cache.get(&name) {
-            cached.clone()
-        } else {
-            let private_n = self.private_n;
-            self.private_n += 1;
-
-            let mangled_name: JsWord = base54(private_n).into();
-
-            self.private_cache
-                .insert(name.clone(), mangled_name.clone());
-
-            mangled_name
-        }
-    }
 }
 
 pub fn mangle_properties<'a>(m: &mut Module, options: ManglePropertiesOptions) {
@@ -309,8 +290,4 @@ impl VisitMut for Mangler<'_> {
             }
         }
     }
-
-    fn visit_mut_private_name(&mut self, private_name: &mut PrivateName) {
-        private_name.id.sym = self.state.gen_private_name(&private_name.id.sym);
-    }
 }

ecmascript/minifier/src/pass/mod.rs

@@ -4,4 +4,5 @@ pub mod global_defs;
 pub mod hygiene;
 pub mod mangle_names;
 pub mod mangle_props;
-pub mod single;
+pub mod postcompress;
+pub mod precompress;

ecmascript/minifier/src/pass/postcompress.rs

@@ -0,0 +1,76 @@
+use crate::option::CompressOptions;
+use swc_ecma_ast::*;
+use swc_ecma_transforms_base::ext::MapWithMut;
+use swc_ecma_visit::{noop_visit_mut_type, VisitMut, VisitMutWith};
+
+pub fn postcompress_optimizer<'a>(options: &'a CompressOptions) -> impl 'a + VisitMut {
+    PostcompressOptimizer { options }
+}
+
+struct PostcompressOptimizer<'a> {
+    options: &'a CompressOptions,
+}
+
+impl PostcompressOptimizer<'_> {
+    fn optimize_in_bool_ctx(&mut self, e: &mut Expr) {
+        if !self.options.bools {
+            return;
+        }
+
+        // Note: `||` is not handled because of precedence.
+        match e {
+            Expr::Bin(BinExpr {
+                op: op @ op!("&&"),
+                right,
+                left,
+                ..
+            }) => {
+                match &**left {
+                    Expr::Bin(BinExpr { op: op!("&&"), .. }) => return,
+                    _ => {}
+                }
+
+                match &mut **right {
+                    Expr::Unary(UnaryExpr {
+                        op: op!("!"), arg, ..
+                    }) if arg.is_ident() => {
+                        let new_op = if *op == op!("&&") {
+                            op!("||")
+                        } else {
+                            op!("&&")
+                        };
+
+                        log::debug!(
+                            "bools: `(a {} !b)` => `(a {} b)` (in bool context)",
+                            *op,
+                            new_op
+                        );
+                        *op = new_op;
+                        *right = arg.take();
+                        return;
+                    }
+
+                    _ => {}
+                }
+            }
+
+            _ => {}
+        }
+    }
+}
+
+impl VisitMut for PostcompressOptimizer<'_> {
+    noop_visit_mut_type!();
+
+    fn visit_mut_cond_expr(&mut self, e: &mut CondExpr) {
+        e.visit_mut_children_with(self);
+
+        self.optimize_in_bool_ctx(&mut *e.test);
+    }
+
+    fn visit_mut_if_stmt(&mut self, s: &mut IfStmt) {
+        s.visit_mut_children_with(self);
+
+        self.optimize_in_bool_ctx(&mut *s.test);
+    }
+}

ecmascript/minifier/src/pass/precompress.rs

@@ -9,10 +9,11 @@ use swc_ecma_transforms_base::ext::MapWithMut;
 use swc_ecma_utils::{ident::IdentLike, Id};
 use swc_ecma_visit::{noop_visit_mut_type, VisitMut, VisitMutWith};
 
+/// Optimizer invoked before invoking compressor.
 ///
 /// - Remove parens.
-pub fn single_pass_optimizer(options: CompressOptions) -> impl VisitMut {
+pub fn precompress_optimizer(options: CompressOptions) -> impl VisitMut {
-    SinglePassOptimizer {
+    PrecompressOptimizer {
         options,
         data: Default::default(),
         fn_decl_count: Default::default(),
@@ -21,7 +22,7 @@ pub fn single_pass_optimizer(options: CompressOptions) -> impl VisitMut {
 }
 
 #[derive(Debug, Default)]
-struct SinglePassOptimizer {
+struct PrecompressOptimizer {
     options: CompressOptions,
     data: ProgramData,
     fn_decl_count: FxHashMap<Id, usize>,
@@ -33,7 +34,7 @@ struct Ctx {
     in_var_pat: bool,
 }
 
-impl VisitMut for SinglePassOptimizer {
+impl VisitMut for PrecompressOptimizer {
     noop_visit_mut_type!();
 
     fn visit_mut_decl(&mut self, n: &mut Decl) {

ecmascript/minifier/src/util/mod.rs

@@ -9,6 +9,7 @@ use swc_ecma_ast::*;
 use swc_ecma_transforms_base::ext::MapWithMut;
 use swc_ecma_utils::ident::IdentLike;
 use swc_ecma_utils::Id;
+use swc_ecma_utils::ModuleItemLike;
 use swc_ecma_utils::StmtLike;
 use swc_ecma_utils::Value;
 use swc_ecma_visit::noop_visit_type;
@@ -26,6 +27,55 @@ pub(crate) fn make_number(span: Span, value: f64) -> Expr {
     Expr::Lit(Lit::Num(Number { span, value }))
 }
 
+pub trait MoudleItemExt: StmtLike + ModuleItemLike {
+    fn as_module_decl(&self) -> Result<&ModuleDecl, &Stmt>;
+
+    fn from_module_item(item: ModuleItem) -> Self;
+
+    fn into_module_item(self) -> ModuleItem {
+        match self.into_module_decl() {
+            Ok(v) => ModuleItem::ModuleDecl(v),
+            Err(v) => ModuleItem::Stmt(v),
+        }
+    }
+
+    fn into_module_decl(self) -> Result<ModuleDecl, Stmt>;
+}
+
+impl MoudleItemExt for Stmt {
+    fn as_module_decl(&self) -> Result<&ModuleDecl, &Stmt> {
+        Err(self)
+    }
+
+    fn from_module_item(item: ModuleItem) -> Self {
+        item.expect_stmt()
+    }
+
+    fn into_module_decl(self) -> Result<ModuleDecl, Stmt> {
+        Err(self)
+    }
+}
+
+impl MoudleItemExt for ModuleItem {
+    fn as_module_decl(&self) -> Result<&ModuleDecl, &Stmt> {
+        match self {
+            ModuleItem::ModuleDecl(v) => Ok(v),
+            ModuleItem::Stmt(v) => Err(v),
+        }
+    }
+
+    fn from_module_item(item: ModuleItem) -> Self {
+        item
+    }
+
+    fn into_module_decl(self) -> Result<ModuleDecl, Stmt> {
+        match self {
+            ModuleItem::ModuleDecl(v) => Ok(v),
+            ModuleItem::Stmt(v) => Err(v),
+        }
+    }
+}
+
 ///
 /// - `!0` for true
 /// - `!1` for false
@@ -45,6 +95,18 @@ pub(crate) trait ExprOptExt: Sized {
     fn as_expr(&self) -> &Expr;
     fn as_mut(&mut self) -> &mut Expr;
 
+    fn first_expr_mut(&mut self) -> &mut Expr {
+        let expr = self.as_mut();
+        match expr {
+            Expr::Seq(seq) => seq
+                .exprs
+                .first_mut()
+                .expect("Sequence expressions should have at least one element")
+                .first_expr_mut(),
+            expr => expr,
+        }
+    }
+
     /// This returns itself for normal expressions and returns last exprssions
     /// for sequence expressions.
     fn value_mut(&mut self) -> &mut Expr {
@@ -279,11 +341,36 @@ where
 #[derive(Default)]
 pub(crate) struct IdentUsageCollector {
     ids: FxHashSet<Id>,
+    ignore_nested: bool,
 }
 
 impl Visit for IdentUsageCollector {
     noop_visit_type!();
 
+    fn visit_block_stmt_or_expr(&mut self, n: &BlockStmtOrExpr, _: &dyn Node) {
+        if self.ignore_nested {
+            return;
+        }
+
+        n.visit_children_with(self);
+    }
+
+    fn visit_constructor(&mut self, n: &Constructor, _: &dyn Node) {
+        if self.ignore_nested {
+            return;
+        }
+
+        n.visit_children_with(self);
+    }
+
+    fn visit_function(&mut self, n: &Function, _: &dyn Node) {
+        if self.ignore_nested {
+            return;
+        }
+
+        n.visit_children_with(self);
+    }
+
     fn visit_ident(&mut self, n: &Ident, _: &dyn Node) {
         self.ids.insert(n.to_id());
     }
@@ -295,13 +382,37 @@ impl Visit for IdentUsageCollector {
             n.prop.visit_with(n, self);
         }
     }
+
+    fn visit_prop_name(&mut self, n: &PropName, _: &dyn Node) {
+        match n {
+            PropName::Computed(..) => {
+                n.visit_children_with(self);
+            }
+            _ => {}
+        }
+    }
 }
 
 pub(crate) fn idents_used_by<N>(n: &N) -> FxHashSet<Id>
 where
     N: VisitWith<IdentUsageCollector>,
 {
-    let mut v = IdentUsageCollector::default();
+    let mut v = IdentUsageCollector {
+        ignore_nested: false,
+        ..Default::default()
+    };
+    n.visit_with(&Invalid { span: DUMMY_SP }, &mut v);
+    v.ids
+}
+
+pub(crate) fn idents_used_by_ignoring_nested<N>(n: &N) -> FxHashSet<Id>
+where
+    N: VisitWith<IdentUsageCollector>,
+{
+    let mut v = IdentUsageCollector {
+        ignore_nested: true,
+        ..Default::default()
+    };
     n.visit_with(&Invalid { span: DUMMY_SP }, &mut v);
     v.ids
 }

ecmascript/minifier/tests/compress.rs

@@ -1,3 +1,5 @@
+extern crate swc_node_base;
+
 use ansi_term::Color;
 use anyhow::bail;
 use anyhow::Context;
@@ -11,6 +13,7 @@ use std::panic::catch_unwind;
 use std::path::Path;
 use std::path::PathBuf;
 use std::process::Command;
+use std::time::Instant;
 use swc_common::comments::SingleThreadedComments;
 use swc_common::errors::Handler;
 use swc_common::sync::Lrc;
@@ -132,6 +135,8 @@ fn run(
 
     let top_level_mark = Mark::fresh(Mark::root());
 
+    let minification_start = Instant::now();
+
     let lexer = Lexer::new(
         Default::default(),
         Default::default(),
@@ -155,8 +160,10 @@ fn run(
         _ => return None,
     };
 
+    let optimization_start = Instant::now();
     let output = optimize(
         program,
+        cm.clone(),
         Some(&comments),
         None,
         &MinifyOptions {
@@ -174,9 +181,22 @@ fn run(
             ..Default::default()
         },
         &ExtraOptions { top_level_mark },
-    )
+    );
-    .fold_with(&mut hygiene())
+    let end = Instant::now();
-    .fold_with(&mut fixer(None));
+    log::info!(
+        "optimize({}) took {:?}",
+        input.display(),
+        end - optimization_start
+    );
+
+    let output = output.fold_with(&mut hygiene()).fold_with(&mut fixer(None));
+
+    let end = Instant::now();
+    log::info!(
+        "process({}) took {:?}",
+        input.display(),
+        end - minification_start
+    );
 
     Some(output)
 }
@@ -199,8 +219,52 @@ fn stdout_of(code: &str) -> Result<String, Error> {
     Ok(String::from_utf8_lossy(&actual_output.stdout).to_string())
 }
 
+fn find_config(dir: &Path) -> String {
+    let mut cur = Some(dir);
+    while let Some(dir) = cur {
+        let config = dir.join("config.json");
+        if config.exists() {
+            let config = read_to_string(&config).expect("failed to read config.json");
+
+            return config;
+        }
+
+        cur = dir.parent();
+    }
+
+    panic!("failed to find config file for {}", dir.display())
+}
+
 #[testing::fixture("tests/compress/fixture/**/input.js")]
 fn base_fixture(input: PathBuf) {
+    let dir = input.parent().unwrap();
+    let config = find_config(&dir);
+    eprintln!("---- {} -----\n{}", Color::Green.paint("Config"), config);
+
+    testing::run_test2(false, |cm, handler| {
+        let output = run(cm.clone(), &handler, &input, &config, None);
+        let output_module = match output {
+            Some(v) => v,
+            None => return Ok(()),
+        };
+
+        let output = print(cm.clone(), &[output_module.clone()], false);
+
+        eprintln!("---- {} -----\n{}", Color::Green.paint("Ouput"), output);
+
+        println!("{}", input.display());
+
+        NormalizedOutput::from(output)
+            .compare_to_file(dir.join("output.js"))
+            .unwrap();
+
+        Ok(())
+    })
+    .unwrap()
+}
+
+#[testing::fixture("tests/projects/files/*.js")]
+fn projects(input: PathBuf) {
     let dir = input.parent().unwrap();
     let config = dir.join("config.json");
     let config = read_to_string(&config).expect("failed to read config.json");
@@ -213,14 +277,19 @@ fn base_fixture(input: PathBuf) {
             None => return Ok(()),
         };
 
-        let output = print(cm.clone(), &[output_module.clone()]);
+        let output = print(cm.clone(), &[output_module.clone()], false);
 
         eprintln!("---- {} -----\n{}", Color::Green.paint("Ouput"), output);
 
         println!("{}", input.display());
 
         NormalizedOutput::from(output)
-            .compare_to_file(dir.join("output.js"))
+            .compare_to_file(
+                dir.parent()
+                    .unwrap()
+                    .join("output")
+                    .join(input.file_name().unwrap()),
+            )
             .unwrap();
 
         Ok(())
@@ -241,7 +310,7 @@ fn base_exec(input: PathBuf) {
 
         let output = run(cm.clone(), &handler, &input, &config, None);
         let output = output.expect("Parsing in base test should not fail");
-        let output = print(cm.clone(), &[output]);
+        let output = print(cm.clone(), &[output], false);
 
         eprintln!(
             "---- {} -----\n{}",
@@ -297,7 +366,7 @@ fn fixture(input: PathBuf) {
             None => return Ok(()),
         };
 
-        let output = print(cm.clone(), &[output_module.clone()]);
+        let output = print(cm.clone(), &[output_module.clone()], false);
 
         eprintln!("---- {} -----\n{}", Color::Green.paint("Ouput"), output);
 
@@ -327,7 +396,7 @@ fn fixture(input: PathBuf) {
                 ModuleItem::Stmt(Stmt::Empty(..)) => false,
                 _ => true,
             });
-            print(cm.clone(), &[expected])
+            print(cm.clone(), &[expected], false)
         };
 
         if output == expected {
@@ -368,7 +437,7 @@ fn fixture(input: PathBuf) {
             });
         }
 
-        let output_str = print(cm.clone(), &[drop_span(output_module.clone())]);
+        let output_str = print(cm.clone(), &[drop_span(output_module.clone())], false);
 
         assert_eq!(DebugUsingDisplay(&output_str), DebugUsingDisplay(&expected));
 
@@ -377,12 +446,12 @@ fn fixture(input: PathBuf) {
     .unwrap()
 }
 
-fn print<N: swc_ecma_codegen::Node>(cm: Lrc<SourceMap>, nodes: &[N]) -> String {
+fn print<N: swc_ecma_codegen::Node>(cm: Lrc<SourceMap>, nodes: &[N], minify: bool) -> String {
     let mut buf = vec![];
 
     {
         let mut emitter = Emitter {
-            cfg: Default::default(),
+            cfg: swc_ecma_codegen::Config { minify },
             cm: cm.clone(),
             comments: None,
             wr: Box::new(JsWriter::new(cm.clone(), "\n", &mut buf, None)),

ecmascript/minifier/tests/compress/fixture/ projects/angular/1/input.js

@@ -0,0 +1,10 @@
+function isUndefined(
+    value
+) {
+    return "undefined" == typeof value;
+}
+function isDefined(
+    value
+) {
+    return "undefined" != typeof value;
+}

ecmascript/minifier/tests/compress/fixture/ projects/angular/1/output.js

@@ -0,0 +1,6 @@
+function isUndefined(value) {
+    return void 0 === value;
+}
+function isDefined(value) {
+    return void 0 !== value;
+}

ecmascript/minifier/tests/compress/fixture/ projects/angular/2/input.js

@@ -0,0 +1,12 @@
+var h = destination.$$hashKey;
+forEach(
+    destination,
+    function (
+        value, key
+    ) {
+        delete destination[key];
+    }
+);
+for (var key in source) destination[key] = copy(
+    source[key]
+);

ecmascript/minifier/tests/compress/fixture/ projects/angular/2/output.js

@@ -0,0 +1,4 @@
+var h = destination.$$hashKey;
+for(var key in forEach(destination, function(value, key) {
+    delete destination[key];
+}), source)destination[key] = copy(source[key]);

ecmascript/minifier/tests/compress/fixture/ projects/angular/3/input.js

@@ -0,0 +1,5 @@
+if (foo) {
+    if (bar) {
+        var baz = console.log('Foo bar');
+    }
+}

ecmascript/minifier/tests/compress/fixture/ projects/angular/3/output.js

@@ -0,0 +1 @@
+if (foo && bar) var baz = console.log("Foo bar");

ecmascript/minifier/tests/compress/fixture/ projects/angular/4/input.js

@@ -0,0 +1,15 @@
+
+export const obj = {
+    eq: function (
+        jqLite,
+        index
+    ) {
+        return index >= 0
+            ? jqLite(
+                this[index]
+            )
+            : jqLite(
+                this[this.length + index]
+            );
+    },
+}

ecmascript/minifier/tests/compress/fixture/ projects/angular/4/output.js

@@ -0,0 +1,5 @@
+export const obj = {
+    eq: function(jqLite, index) {
+        return jqLite(index >= 0 ? this[index] : this[this.length + index]);
+    }
+};

ecmascript/minifier/tests/compress/fixture/ projects/angular/5/input.js

@@ -0,0 +1,24 @@
+function forEach(obj, iterator, context) {
+    var key;
+    if (obj) {
+        if (isFunction(obj)) {
+            for (key in obj) {
+                if (key != 'prototype' && key != 'length' && key != 'name' && obj.hasOwnProperty(key)) {
+                    iterator.call(context, obj[key], key);
+                }
+            }
+        } else if (obj.forEach && obj.forEach !== forEach) {
+            obj.forEach(iterator, context);
+        } else if (isArrayLike(obj)) {
+            for (key = 0; key < obj.length; key++)
+                iterator.call(context, obj[key], key);
+        } else {
+            for (key in obj) {
+                if (obj.hasOwnProperty(key)) {
+                    iterator.call(context, obj[key], key);
+                }
+            }
+        }
+    }
+    return obj;
+}

ecmascript/minifier/tests/compress/fixture/ projects/angular/5/output.js

@@ -0,0 +1,8 @@
+function forEach(obj, iterator, context) {
+    var key;
+    if (obj) if (isFunction(obj)) for(key in obj)"prototype" != key && "length" != key && "name" != key && obj.hasOwnProperty(key) && iterator.call(context, obj[key], key);
+    else if (obj.forEach && obj.forEach !== forEach) obj.forEach(iterator, context);
+    else if (isArrayLike(obj)) for(key = 0; key < obj.length; key++)iterator.call(context, obj[key], key);
+    else for(key in obj)obj.hasOwnProperty(key) && iterator.call(context, obj[key], key);
+    return obj;
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/1/input.js

@@ -0,0 +1,2 @@
+var _ = root._;
+if (!_ && (typeof require !== 'undefined')) _ = require('underscore');

ecmascript/minifier/tests/compress/fixture/ projects/backbone/1/output.js

@@ -0,0 +1,2 @@
+var _ = root._;
+_ || "undefined" == typeof require || (_ = require("underscore"));

ecmascript/minifier/tests/compress/fixture/ projects/backbone/10/input.js

@@ -0,0 +1,15 @@
+
+
+const obj = {
+    _ensureElement: function () {
+        if (!this.el) {
+            var attrs = _.extend({}, _.result(this, 'attributes'));
+            if (this.id) attrs.id = _.result(this, 'id');
+            if (this.className) attrs['class'] = _.result(this, 'className');
+            var $el = Backbone.$('<' + _.result(this, 'tagName') + '>').attr(attrs);
+            this.setElement($el, false);
+        } else {
+            this.setElement(_.result(this, 'el'), false);
+        }
+    }
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/10/output.js

@@ -0,0 +1,12 @@
+const obj = {
+    _ensureElement: function() {
+        if (this.el) this.setElement(_.result(this, "el"), !1);
+        else {
+            var attrs = _.extend({
+            }, _.result(this, "attributes"));
+            this.id && (attrs.id = _.result(this, "id")), this.className && (attrs.class = _.result(this, "className"));
+            var $el = Backbone.$("<" + _.result(this, "tagName") + ">").attr(attrs);
+            this.setElement($el, !1);
+        }
+    }
+};

ecmascript/minifier/tests/compress/fixture/ projects/backbone/11/input.js

@@ -0,0 +1,8 @@
+
+
+const obj = {
+    navigate: function (fragment, options) {
+        if (!History.started) return false;
+        if (!options || options === true) options = { trigger: !!options };
+    }
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/11/output.js

@@ -0,0 +1,8 @@
+const obj = {
+    navigate: function(fragment, options) {
+        if (!History.started) return !1;
+        options && !0 !== options || (options = {
+            trigger: !!options
+        });
+    }
+};

ecmascript/minifier/tests/compress/fixture/ projects/backbone/12/input.js

@@ -0,0 +1,6 @@
+var names, i, l;
+
+names = name ? [name] : _.keys(this._events);
+for (i = 0, l = names.length; i < l; i++) {
+    name = names[i];
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/12/output.js

@@ -0,0 +1,2 @@
+var names, i, l;
+for(i = 0, l = (names = name ? [name] : _.keys(this._events)).length; i < l; i++)name = names[i];

ecmascript/minifier/tests/compress/fixture/ projects/backbone/13/input.js

@@ -0,0 +1,10 @@
+export const obj = {
+    _validate: function (attrs, options) {
+        if (!options.validate || !this.validate) return true;
+        attrs = _.extend({}, this.attributes, attrs);
+        var error = this.validationError = this.validate(attrs, options) || null;
+        if (!error) return true;
+        this.trigger('invalid', this, error, _.extend(options, { validationError: error }));
+        return false;
+    }
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/13/output.js

@@ -0,0 +1,11 @@
+export const obj = {
+    _validate: function(attrs, options) {
+        if (!options.validate || !this.validate) return !0;
+        attrs = _.extend({
+        }, this.attributes, attrs);
+        var error = this.validationError = this.validate(attrs, options) || null;
+        return !error || (this.trigger("invalid", this, error, _.extend(options, {
+            validationError: error
+        })), !1);
+    }
+};

ecmascript/minifier/tests/compress/fixture/ projects/backbone/14/input.js

@@ -0,0 +1,68 @@
+export const obj = {
+    set: function (key, val, options) {
+        var attr, attrs, unset, changes, silent, changing, prev, current;
+        if (key == null) return this;
+
+        // Handle both `"key", value` and `{key: value}` -style arguments.
+        if (typeof key === 'object') {
+            attrs = key;
+            options = val;
+        } else {
+            (attrs = {})[key] = val;
+        }
+
+        options || (options = {});
+
+        // Run validation.
+        if (!this._validate(attrs, options)) return false;
+
+        // Extract attributes and options.
+        unset = options.unset;
+        silent = options.silent;
+        changes = [];
+        changing = this._changing;
+        this._changing = true;
+
+        if (!changing) {
+            this._previousAttributes = _.clone(this.attributes);
+            this.changed = {};
+        }
+        current = this.attributes, prev = this._previousAttributes;
+
+        // Check for changes of `id`.
+        if (this.idAttribute in attrs) this.id = attrs[this.idAttribute];
+
+        // For each `set` attribute, update or delete the current value.
+        for (attr in attrs) {
+            val = attrs[attr];
+            if (!_.isEqual(current[attr], val)) changes.push(attr);
+            if (!_.isEqual(prev[attr], val)) {
+                this.changed[attr] = val;
+            } else {
+                delete this.changed[attr];
+            }
+            unset ? delete current[attr] : current[attr] = val;
+        }
+
+        // Trigger all relevant attribute changes.
+        if (!silent) {
+            if (changes.length) this._pending = true;
+            for (var i = 0, l = changes.length; i < l; i++) {
+                this.trigger('change:' + changes[i], this, current[changes[i]], options);
+            }
+        }
+
+        // You might be wondering why there's a `while` loop here. Changes can
+        // be recursively nested within `"change"` events.
+        if (changing) return this;
+        if (!silent) {
+            while (this._pending) {
+                this._pending = false;
+                this.trigger('change', this, options);
+            }
+        }
+        this._pending = false;
+        this._changing = false;
+        return this;
+    },
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/14/output.js

@@ -0,0 +1,18 @@
+export const obj = {
+    set: function(key, val, options) {
+        var attr, attrs, unset, changes, silent, changing, prev, current;
+        if (null == key) return this;
+        if ("object" == typeof key ? (attrs = key, options = val) : (attrs = {
+        })[key] = val, options || (options = {
+        }), !this._validate(attrs, options)) return !1;
+        for(attr in unset = options.unset, silent = options.silent, changes = [], changing = this._changing, this._changing = !0, changing || (this._previousAttributes = _.clone(this.attributes), this.changed = {
+        }), current = this.attributes, prev = this._previousAttributes, this.idAttribute in attrs && (this.id = attrs[this.idAttribute]), attrs)val = attrs[attr], _.isEqual(current[attr], val) || changes.push(attr), _.isEqual(prev[attr], val) ? delete this.changed[attr] : this.changed[attr] = val, unset ? delete current[attr] : current[attr] = val;
+        if (!silent) {
+            changes.length && (this._pending = !0);
+            for(var i = 0, l = changes.length; i < l; i++)this.trigger("change:" + changes[i], this, current[changes[i]], options);
+        }
+        if (changing) return this;
+        if (!silent) for(; this._pending;)this._pending = !1, this.trigger("change", this, options);
+        return this._pending = !1, this._changing = !1, this;
+    }
+};

ecmascript/minifier/tests/compress/fixture/ projects/backbone/15/input.js

@@ -0,0 +1,12 @@
+export const obj = {
+    changedAttributes: function (diff) {
+        if (!diff) return this.hasChanged() ? _.clone(this.changed) : false;
+        var val, changed = false;
+        var old = this._changing ? this._previousAttributes : this.attributes;
+        for (var attr in diff) {
+            if (_.isEqual(old[attr], (val = diff[attr]))) continue;
+            (changed || (changed = {}))[attr] = val;
+        }
+        return changed;
+    }
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/15/output.js

@@ -0,0 +1,9 @@
+export const obj = {
+    changedAttributes: function(diff) {
+        if (!diff) return !!this.hasChanged() && _.clone(this.changed);
+        var val, changed = !1, old = this._changing ? this._previousAttributes : this.attributes;
+        for(var attr in diff)_.isEqual(old[attr], val = diff[attr]) || ((changed || (changed = {
+        }))[attr] = val);
+        return changed;
+    }
+};

ecmascript/minifier/tests/compress/fixture/ projects/backbone/16/input.js

@@ -0,0 +1,23 @@
+export const obj = {
+    remove: function (models, options) {
+        var singular = !_.isArray(models);
+        models = singular ? [models] : _.clone(models);
+        options || (options = {});
+        var i, l, index, model;
+        for (i = 0, l = models.length; i < l; i++) {
+            model = models[i] = this.get(models[i]);
+            if (!model) continue;
+            delete this._byId[model.id];
+            delete this._byId[model.cid];
+            index = this.indexOf(model);
+            this.models.splice(index, 1);
+            this.length--;
+            if (!options.silent) {
+                options.index = index;
+                model.trigger('remove', model, this, options);
+            }
+            this._removeReference(model);
+        }
+        return singular ? models[0] : models;
+    },
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/16/output.js

@@ -0,0 +1,8 @@
+export const obj = {
+    remove: function(models, options) {
+        var i, l, index, model, singular = !_.isArray(models);
+        for(options || (options = {
+        }), i = 0, l = (models = singular ? [models] : _.clone(models)).length; i < l; i++)(model = models[i] = this.get(models[i])) && (delete this._byId[model.id], delete this._byId[model.cid], index = this.indexOf(model), this.models.splice(index, 1), this.length--, options.silent || (options.index = index, model.trigger("remove", model, this, options)), this._removeReference(model));
+        return singular ? models[0] : models;
+    }
+};

ecmascript/minifier/tests/compress/fixture/ projects/backbone/17/input.js

@@ -0,0 +1,15 @@
+export const obj = {
+    create: function (model, options) {
+        options = options ? _.clone(options) : {};
+        if (!(model = this._prepareModel(model, options))) return false;
+        if (!options.wait) this.add(model, options);
+        var collection = this;
+        var success = options.success;
+        options.success = function (model, resp, options) {
+            if (options.wait) collection.add(model, options);
+            if (success) success(model, resp, options);
+        };
+        model.save(null, options);
+        return model;
+    },
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/17/output.js

@@ -0,0 +1,11 @@
+export const obj = {
+    create: function(model, options) {
+        if (options = options ? _.clone(options) : {
+        }, !(model = this._prepareModel(model, options))) return !1;
+        options.wait || this.add(model, options);
+        var collection = this, success = options.success;
+        return options.success = function(model, resp, options) {
+            options.wait && collection.add(model, options), success && success(model, resp, options);
+        }, model.save(null, options), model;
+    }
+};

ecmascript/minifier/tests/compress/fixture/ projects/backbone/18/input.js

@@ -0,0 +1,11 @@
+export const obj = {
+    _routeToRegExp: function (route) {
+        route = route.replace(escapeRegExp, '\\$&')
+            .replace(optionalParam, '(?:$1)?')
+            .replace(namedParam, function (match, optional) {
+                return optional ? match : '([^\/]+)';
+            })
+            .replace(splatParam, '(.*?)');
+        return new RegExp('^' + route + '$');
+    }
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/18/output.js

@@ -0,0 +1,7 @@
+export const obj = {
+    _routeToRegExp: function(route) {
+        return route = route.replace(escapeRegExp, "\\$&").replace(optionalParam, "(?:$1)?").replace(namedParam, function(match, optional) {
+            return optional ? match : "([^/]+)";
+        }).replace(splatParam, "(.*?)"), new RegExp("^" + route + "$");
+    }
+};

ecmascript/minifier/tests/compress/fixture/ projects/backbone/19/input.js

@@ -0,0 +1,40 @@
+export const obj = {
+    navigate: function (fragment, options) {
+        if (!History.started) return false;
+        if (!options || options === true) options = { trigger: !!options };
+
+        var url = this.root + (fragment = this.getFragment(fragment || ''));
+
+        // Strip the fragment of the query and hash for matching.
+        fragment = fragment.replace(pathStripper, '');
+
+        if (this.fragment === fragment) return;
+        this.fragment = fragment;
+
+        // Don't include a trailing slash on the root.
+        if (fragment === '' && url !== '/') url = url.slice(0, -1);
+
+        // If pushState is available, we use it to set the fragment as a real URL.
+        if (this._hasPushState) {
+            this.history[options.replace ? 'replaceState' : 'pushState']({}, document.title, url);
+
+            // If hash changes haven't been explicitly disabled, update the hash
+            // fragment to store history.
+        } else if (this._wantsHashChange) {
+            this._updateHash(this.location, fragment, options.replace);
+            if (this.iframe && (fragment !== this.getFragment(this.getHash(this.iframe)))) {
+                // Opening and closing the iframe tricks IE7 and earlier to push a
+                // history entry on hash-tag change.  When replace is true, we don't
+                // want this.
+                if (!options.replace) this.iframe.document.open().close();
+                this._updateHash(this.iframe.location, fragment, options.replace);
+            }
+
+            // If you've told us that you explicitly don't want fallback hashchange-
+            // based history, then `navigate` becomes a page refresh.
+        } else {
+            return this.location.assign(url);
+        }
+        if (options.trigger) return this.loadUrl(fragment);
+    },
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/19/output.js

@@ -0,0 +1,18 @@
+export const obj = {
+    navigate: function(fragment, options) {
+        if (!History.started) return !1;
+        options && !0 !== options || (options = {
+            trigger: !!options
+        });
+        var url = this.root + (fragment = this.getFragment(fragment || ""));
+        if (fragment = fragment.replace(pathStripper, ""), this.fragment !== fragment) {
+            if (this.fragment = fragment, "" === fragment && "/" !== url && (url = url.slice(0, -1)), this._hasPushState) this.history[options.replace ? "replaceState" : "pushState"]({
+            }, document.title, url);
+            else {
+                if (!this._wantsHashChange) return this.location.assign(url);
+                this._updateHash(this.location, fragment, options.replace), this.iframe && fragment !== this.getFragment(this.getHash(this.iframe)) && (options.replace || this.iframe.document.open().close(), this._updateHash(this.iframe.location, fragment, options.replace));
+            }
+            if (options.trigger) return this.loadUrl(fragment);
+        }
+    }
+};

ecmascript/minifier/tests/compress/fixture/ projects/backbone/2/input.js

@@ -0,0 +1,13 @@
+function foo() {
+    if (!eventsApi(this, "on", name, [callback, context]) || !callback)
+        return this;
+    return (
+        this._events || (this._events = {}),
+        (this._events[name] || (this._events[name] = [])).push({
+            callback: callback,
+            context: context,
+            ctx: context || this,
+        }),
+        this
+    );
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/2/output.js

@@ -0,0 +1,9 @@
+function foo() {
+    return eventsApi(this, "on", name, [callback,
+        context]) && callback && (this._events || (this._events = {
+    }), (this._events[name] || (this._events[name] = [])).push({
+        callback: callback,
+        context: context,
+        ctx: context || this
+    })), this;
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/20/input.js

@@ -0,0 +1,92 @@
+export const E = {
+    set: function (models, options) {
+        options = _.defaults({}, options, setOptions);
+        if (options.parse) models = this.parse(models, options);
+        var singular = !_.isArray(models);
+        models = singular ? (models ? [models] : []) : _.clone(models);
+        var i, l, id, model, attrs, existing, sort;
+        var at = options.at;
+        var targetModel = this.model;
+        var sortable = this.comparator && (at == null) && options.sort !== false;
+        var sortAttr = _.isString(this.comparator) ? this.comparator : null;
+        var toAdd = [], toRemove = [], modelMap = {};
+        var add = options.add, merge = options.merge, remove = options.remove;
+        var order = !sortable && add && remove ? [] : false;
+
+        // Turn bare objects into model references, and prevent invalid models
+        // from being added.
+        for (i = 0, l = models.length; i < l; i++) {
+            attrs = models[i];
+            if (attrs instanceof Model) {
+                id = model = attrs;
+            } else {
+                id = attrs[targetModel.prototype.idAttribute];
+            }
+
+            // If a duplicate is found, prevent it from being added and
+            // optionally merge it into the existing model.
+            if (existing = this.get(id)) {
+                if (remove) modelMap[existing.cid] = true;
+                if (merge) {
+                    attrs = attrs === model ? model.attributes : attrs;
+                    if (options.parse) attrs = existing.parse(attrs, options);
+                    existing.set(attrs, options);
+                    if (sortable && !sort && existing.hasChanged(sortAttr)) sort = true;
+                }
+                models[i] = existing;
+
+                // If this is a new, valid model, push it to the `toAdd` list.
+            } else if (add) {
+                model = models[i] = this._prepareModel(attrs, options);
+                if (!model) continue;
+                toAdd.push(model);
+
+                // Listen to added models' events, and index models for lookup by
+                // `id` and by `cid`.
+                model.on('all', this._onModelEvent, this);
+                this._byId[model.cid] = model;
+                if (model.id != null) this._byId[model.id] = model;
+            }
+            if (order) order.push(existing || model);
+        }
+
+        // Remove nonexistent models if appropriate.
+        if (remove) {
+            for (i = 0, l = this.length; i < l; ++i) {
+                if (!modelMap[(model = this.models[i]).cid]) toRemove.push(model);
+            }
+            if (toRemove.length) this.remove(toRemove, options);
+        }
+
+        // See if sorting is needed, update `length` and splice in new models.
+        if (toAdd.length || (order && order.length)) {
+            if (sortable) sort = true;
+            this.length += toAdd.length;
+            if (at != null) {
+                for (i = 0, l = toAdd.length; i < l; i++) {
+                    this.models.splice(at + i, 0, toAdd[i]);
+                }
+            } else {
+                if (order) this.models.length = 0;
+                var orderedModels = order || toAdd;
+                for (i = 0, l = orderedModels.length; i < l; i++) {
+                    this.models.push(orderedModels[i]);
+                }
+            }
+        }
+
+        // Silently sort the collection if appropriate.
+        if (sort) this.sort({ silent: true });
+
+        // Unless silenced, it's time to fire all appropriate add/sort events.
+        if (!options.silent) {
+            for (i = 0, l = toAdd.length; i < l; i++) {
+                (model = toAdd[i]).trigger('add', model, this, options);
+            }
+            if (sort || (order && order.length)) this.trigger('sort', this, options);
+        }
+
+        // Return the added (or merged) model (or models).
+        return singular ? models[0] : models;
+    }
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/20/output.js

@@ -0,0 +1,35 @@
+export const E = {
+    set: function(models, options) {
+        (options = _.defaults({
+        }, options, setOptions)).parse && (models = this.parse(models, options));
+        var singular = !_.isArray(models);
+        models = singular ? models ? [models] : [] : _.clone(models);
+        var i, l, id, model, attrs, existing, sort, at = options.at, targetModel = this.model, sortable = this.comparator && null == at && !1 !== options.sort, sortAttr = _.isString(this.comparator) ? this.comparator : null, toAdd = [], toRemove = [], modelMap = {
+        }, add = options.add, merge = options.merge, remove = options.remove, order = !sortable && !!add && !!remove && [];
+        for(i = 0, l = models.length; i < l; i++){
+            if (id = (attrs = models[i]) instanceof Model ? model = attrs : attrs[targetModel.prototype.idAttribute], existing = this.get(id)) remove && (modelMap[existing.cid] = !0), merge && (attrs = attrs === model ? model.attributes : attrs, options.parse && (attrs = existing.parse(attrs, options)), existing.set(attrs, options), sortable && !sort && existing.hasChanged(sortAttr) && (sort = !0)), models[i] = existing;
+            else if (add) {
+                if (!(model = models[i] = this._prepareModel(attrs, options))) continue;
+                toAdd.push(model), model.on("all", this._onModelEvent, this), this._byId[model.cid] = model, null != model.id && (this._byId[model.id] = model);
+            }
+            order && order.push(existing || model);
+        }
+        if (remove) {
+            for(i = 0, l = this.length; i < l; ++i)modelMap[(model = this.models[i]).cid] || toRemove.push(model);
+            toRemove.length && this.remove(toRemove, options);
+        }
+        if (toAdd.length || order && order.length) if (sortable && (sort = !0), this.length += toAdd.length, null != at) for(i = 0, l = toAdd.length; i < l; i++)this.models.splice(at + i, 0, toAdd[i]);
+        else {
+            order && (this.models.length = 0);
+            var orderedModels = order || toAdd;
+            for(i = 0, l = orderedModels.length; i < l; i++)this.models.push(orderedModels[i]);
+        }
+        if (sort && this.sort({
+            silent: !0
+        }), !options.silent) {
+            for(i = 0, l = toAdd.length; i < l; i++)(model = toAdd[i]).trigger("add", model, this, options);
+            (sort || order && order.length) && this.trigger("sort", this, options);
+        }
+        return singular ? models[0] : models;
+    }
+};

ecmascript/minifier/tests/compress/fixture/ projects/backbone/3/input.js

@@ -0,0 +1,4 @@
+
+if (!name && !callback && !context) {
+    console.log('foo')
+}

ecmascript/minifier/tests/compress/fixture/ projects/backbone/3/output.js

@@ -0,0 +1 @@
+name || callback || context || console.log("foo");