Improve optimizer (#660)

Although it's quite naive at the moment, I added two optimization passes.

 - dead code elimination (Closes #607)
 - inlining

common/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "swc_common"
-version = "0.5.2"
+version = "0.5.3"
 authors = ["강동윤 <kdy1997.dev@gmail.com>"]
 license = "Apache-2.0/MIT"
 repository = "https://github.com/swc-project/swc.git"

common/src/fold/and_then.rs

@@ -1,5 +1,9 @@
 use super::{Fold, FoldWith, Visit, VisitWith};
-use crate::util::move_map::MoveMap;
+use crate::{
+    pass::{CompilerPass, Repeated, RepeatedPass},
+    util::move_map::MoveMap,
+};
+use std::borrow::Cow;
 
 #[macro_export]
 macro_rules! chain {
@@ -90,3 +94,35 @@ where
         self.second.visit(node);
     }
 }
+
+impl<A, B> CompilerPass for AndThen<A, B>
+where
+    A: CompilerPass,
+    B: CompilerPass,
+{
+    fn name() -> Cow<'static, str> {
+        format!("{} -> {}", A::name(), B::name()).into()
+    }
+}
+
+impl<A, B, At> RepeatedPass<At> for AndThen<A, B>
+where
+    A: RepeatedPass<At>,
+    B: RepeatedPass<At>,
+{
+}
+
+impl<A, B> Repeated for AndThen<A, B>
+where
+    A: Repeated,
+    B: Repeated,
+{
+    fn changed(&self) -> bool {
+        self.first.changed() || self.second.changed()
+    }
+
+    fn reset(&mut self) {
+        self.first.reset();
+        self.second.reset();
+    }
+}

common/src/lib.rs

@@ -24,6 +24,7 @@ pub mod fold;
 pub mod input;
 pub mod iter;
 pub mod macros;
+pub mod pass;
 mod pos;
 mod rustc_data_structures;
 pub mod serializer;

common/src/pass.rs

@@ -0,0 +1,85 @@
+use crate::{Fold, FoldWith};
+use serde::export::PhantomData;
+use std::borrow::Cow;
+
+pub trait CompilerPass {
+    /// Name should follow hyphen-case
+    ///
+    /// TODO: timing
+    fn name() -> Cow<'static, str>;
+}
+
+pub trait Repeated: CompilerPass {
+    /// Should run again?
+    fn changed(&self) -> bool;
+
+    /// Reset.
+    fn reset(&mut self);
+}
+
+pub trait RepeatedPass<At>: Repeated + CompilerPass {}
+
+impl<T, P> RepeatedPass<T> for P where P: CompilerPass + Repeated {}
+
+#[derive(Debug, Copy, Clone)]
+pub struct Repeat<P, At>
+where
+    P: RepeatedPass<At>,
+{
+    pass: P,
+    at: PhantomData<At>,
+}
+
+impl<P, At> Repeat<P, At>
+where
+    P: RepeatedPass<At>,
+{
+    pub fn new(pass: P) -> Self {
+        Self {
+            pass,
+            at: PhantomData,
+        }
+    }
+}
+
+impl<P, At> CompilerPass for Repeat<P, At>
+where
+    P: RepeatedPass<At>,
+{
+    fn name() -> Cow<'static, str> {
+        format!("Repeat({})", P::name()).into()
+    }
+}
+
+impl<P, At> Repeated for Repeat<P, At>
+where
+    P: RepeatedPass<At>,
+{
+    fn changed(&self) -> bool {
+        self.pass.changed()
+    }
+
+    fn reset(&mut self) {
+        self.pass.reset()
+    }
+}
+
+#[cfg(feature = "fold")]
+impl<P, At> Fold<At> for Repeat<P, At>
+where
+    At: FoldWith<Self> + FoldWith<P>,
+    P: RepeatedPass<At>,
+{
+    fn fold(&mut self, mut node: At) -> At {
+        loop {
+            self.pass.reset();
+            node = node.fold_with(&mut self.pass);
+
+            if !self.pass.changed() {
+                break;
+            }
+        }
+
+        node
+    }
+}

ecmascript/parser/Cargo.toml

@@ -22,7 +22,7 @@ swc_ecma_ast = { version = "0.17.0", path ="../ast" }
 swc_ecma_parser_macros = { version = "0.4", path ="./macros" }
 enum_kind = { version = "0.2", path ="../../macros/enum_kind" }
 unicode-xid = "0.2"
-log = { version = "0.4", features = ["release_max_level_debug"] }
+log = "0.4"
 either = { version = "1.4" }
 serde = { version = "1", features = ["derive"] }
 smallvec = "1"

ecmascript/transforms/Cargo.toml

@@ -30,6 +30,7 @@ arrayvec = "0.5.1"
 serde_json = "1"
 smallvec = "1"
 is-macro = "0.1"
+log = "0.4.8"
 
 [dev-dependencies]
 testing = { version = "0.5", path ="../../testing" }

ecmascript/transforms/src/compat/es2015/regenerator/case.rs

@@ -49,7 +49,7 @@ pub(super) struct CaseHandler<'a> {
     listing_len: usize,
 
     /// A sparse array whose keys correspond to locations in this.listing
-    /// that have been marked as branch/jump targets.
+    /// that have been marked as stmt/jump targets.
     marked: Vec<Loc>,
 
     leaps: LeapManager,

ecmascript/transforms/src/fixer.rs

@@ -149,6 +149,24 @@ impl Fold<Stmt> for Fixer {
     }
 }
 
+impl Fold<IfStmt> for Fixer {
+    fn fold(&mut self, node: IfStmt) -> IfStmt {
+        let node: IfStmt = node.fold_children(self);
+
+        match *node.cons {
+            Stmt::If(..) => IfStmt {
+                cons: box Stmt::Block(BlockStmt {
+                    span: node.cons.span(),
+                    stmts: vec![*node.cons],
+                }),
+                ..node
+            },
+
+            _ => node,
+        }
+    }
+}
+
 macro_rules! context_fn_args {
     ($T:tt, $is_new:expr) => {
         impl Fold<$T> for Fixer {
@@ -510,6 +528,17 @@ impl Fold<Expr> for Fixer {
                     }
 
                     e @ Expr::Seq(..)
+                    | e @ Expr::Update(..)
+                    | e
+                    @
+                    Expr::Unary(UnaryExpr {
+                        op: op!("delete"), ..
+                    })
+                    | e
+                    @
+                    Expr::Unary(UnaryExpr {
+                        op: op!("void"), ..
+                    })
                     | e @ Expr::Yield(..)
                     | e @ Expr::Cond(..)
                     | e @ Expr::Assign(..)
@@ -1039,4 +1068,6 @@ var store = global[SHARED] || (global[SHARED] = {});
     foo: 1
 });"
     );
+
+    test_fixer!(void_and_bin, "(void 0) * 2", "(void 0) * 2");
 }

ecmascript/transforms/src/optimization.rs

@@ -1,9 +1,5 @@
-pub use self::{
-    inline_globals::InlineGlobals,
-    json_parse::JsonParse,
-    simplify::{expr_simplifier, simplifier},
-};
+pub use self::{inline_globals::InlineGlobals, json_parse::JsonParse, simplify::simplifier};
 
 mod inline_globals;
 mod json_parse;
-mod simplify;
+pub mod simplify;

ecmascript/transforms/src/optimization/simplify.rs

@@ -1,30 +0,0 @@
-//! Ported from closure compiler.
-pub use self::dce::dce;
-use self::expr::SimplifyExpr;
-use crate::pass::Pass;
-use swc_common::{Fold, FoldWith};
-use swc_ecma_ast::*;
-
-pub mod dce;
-mod expr;
-
-/// Not intended for general use. Use [simplifier] instead.
-///
-/// Ported from `PeepholeFoldConstants` of google closure compler.
-pub fn expr_simplifier() -> impl Pass + 'static {
-    SimplifyExpr
-}
-
-/// Ported from `PeepholeRemoveDeadCode` and `PeepholeFoldConstants` of google
-/// closure compiler.
-pub fn simplifier() -> impl Pass + 'static {
-    Simplifier
-}
-
-struct Simplifier;
-
-impl Fold<Program> for Simplifier {
-    fn fold(&mut self, p: Program) -> Program {
-        p.fold_with(&mut expr_simplifier()).fold_with(&mut dce())
-    }
-}

ecmascript/transforms/src/optimization/simplify/branch/tests.rs

@@ -1,12 +1,11 @@
-use super::dce;
-use crate::optimization::expr_simplifier;
+use super::{super::expr_simplifier, dead_branch_remover};
 use swc_common::chain;
 
 macro_rules! test_stmt {
     ($l:expr, $r:expr) => {
         test_transform!(
             ::swc_ecma_parser::Syntax::default(),
-            |_| chain!(expr_simplifier(), dce()),
+            |_| chain!(expr_simplifier(), dead_branch_remover()),
             $l,
             $r
         )
@@ -1662,3 +1661,63 @@ fn test_function_call_references_setter_is_not_removed() {
         "foo();",
     ));
 }
+
+#[test]
+fn custom_loop_1() {
+    test(
+        "let b = 2;
+
+let a = 1;
+if (2) {
+a = 2;
+}
+
+let c;
+if (a) {
+c = 3;
+}",
+        "let b = 2;
+
+let a = 1;
+a = 2;
+
+let c;
+if (a) c = 3;",
+    );
+}
+
+#[test]
+fn custom_loop_2() {
+    test(
+        "let b = 2;
+
+let a = 1;
+if (2) {
+a = 2;
+}
+
+let c;
+if (a) {
+c = 3;
+}",
+        "let b = 2;
+
+let a = 1;
+a = 2;
+
+let c;
+if (a) c = 3;",
+    );
+}
+
+#[test]
+fn custom_loop_3() {
+    test(
+        "let c;
+if (2) c = 3;
+console.log(c);",
+        "let c;
+c = 3;
+console.log(c);",
+    );
+}

ecmascript/transforms/src/optimization/simplify/dce/decl.rs

@@ -0,0 +1,67 @@
+use super::Dce;
+use swc_common::{Fold, FoldWith, Spanned};
+use swc_ecma_ast::*;
+use swc_ecma_utils::{find_ids, ident::IdentLike};
+
+impl Fold<FnDecl> for Dce<'_> {
+    fn fold(&mut self, mut f: FnDecl) -> FnDecl {
+        if self.is_marked(f.span()) {
+            return f;
+        }
+
+        if self.marking_phase || self.included.contains(&f.ident.to_id()) {
+            f.function.span = f.function.span.apply_mark(self.config.used_mark);
+            f.function.body = self.fold_in_marking_phase(f.function.body);
+        }
+
+        f.fold_children(self)
+    }
+}
+
+impl Fold<ClassDecl> for Dce<'_> {
+    fn fold(&mut self, mut node: ClassDecl) -> ClassDecl {
+        if self.is_marked(node.span()) {
+            return node;
+        }
+
+        if self.marking_phase || self.included.contains(&node.ident.to_id()) {
+            node.class.span = node.class.span.apply_mark(self.config.used_mark);
+        }
+
+        node.fold_children(self)
+    }
+}
+
+impl Fold<VarDecl> for Dce<'_> {
+    fn fold(&mut self, var: VarDecl) -> VarDecl {
+        if self.is_marked(var.span) {
+            return var;
+        }
+
+        let var: VarDecl = var.fold_children(self);
+
+        if self.included.is_empty() {
+            return var;
+        }
+
+        let ids: Vec<Ident> = find_ids(&var.decls);
+
+        for i in ids {
+            for i1 in &self.included {
+                if i1.0 == i.sym && i1.1 == i.span.ctxt() {
+                    return VarDecl {
+                        span: var.span.apply_mark(self.config.used_mark),
+                        ..var
+                    };
+                }
+            }
+        }
+
+        var
+    }
+}
+
+preserve!(TsInterfaceDecl);
+preserve!(TsTypeAliasDecl);
+preserve!(TsEnumDecl);
+preserve!(TsModuleDecl);

ecmascript/transforms/src/optimization/simplify/dce/module_decl.rs

@@ -0,0 +1,149 @@
+use super::Dce;
+use swc_common::{Fold, FoldWith};
+use swc_ecma_ast::*;
+use swc_ecma_utils::find_ids;
+
+impl Fold<ImportDecl> for Dce<'_> {
+    fn fold(&mut self, import: ImportDecl) -> ImportDecl {
+        if self.is_marked(import.span) {
+            return import;
+        }
+
+        let mut import: ImportDecl = import.fold_children(self);
+
+        // Side effect import
+        if import.specifiers.is_empty() {
+            import.span = import.span.apply_mark(self.config.used_mark);
+            return import;
+        }
+
+        // First run.
+        if self.included.is_empty() {
+            return import;
+        }
+
+        // TODO: Drop unused imports.
+        //      e.g) import { foo, bar } from './foo';
+        //           foo()
+
+        let ids: Vec<Ident> = find_ids(&import.specifiers);
+
+        for id in ids {
+            for c in &self.included {
+                if c.0 == id.sym && c.1 == id.span.ctxt() {
+                    import.span = import.span.apply_mark(self.config.used_mark);
+                    return import;
+                }
+            }
+        }
+
+        import
+    }
+}
+
+impl Fold<ExportDecl> for Dce<'_> {
+    fn fold(&mut self, mut node: ExportDecl) -> ExportDecl {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        let i = match node.decl {
+            Decl::Class(ClassDecl { ref ident, .. }) | Decl::Fn(FnDecl { ref ident, .. }) => ident,
+
+            // Preserve types
+            Decl::TsInterface(_) | Decl::TsTypeAlias(_) | Decl::TsEnum(_) | Decl::TsModule(_) => {
+                node.span = node.span.apply_mark(self.config.used_mark);
+                return node;
+            }
+
+            // Preserve only exported variables
+            Decl::Var(ref mut v) => {
+                // If config.used is None, all exports are preserved
+                if let Some(..) = self.config.used {
+                    v.decls.retain(|d| self.should_include(d));
+                }
+
+                if !v.decls.is_empty() {
+                    node.span = node.span.apply_mark(self.config.used_mark);
+                    node.decl = self.fold_in_marking_phase(node.decl);
+                }
+                return node;
+            }
+        };
+
+        if self.is_exported(&i.sym) {
+            node.span = node.span.apply_mark(self.config.used_mark);
+            node.decl = self.fold_in_marking_phase(node.decl);
+        }
+
+        node
+    }
+}
+
+impl Fold<ExportDefaultExpr> for Dce<'_> {
+    fn fold(&mut self, mut node: ExportDefaultExpr) -> ExportDefaultExpr {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        if self.is_exported(&js_word!("default")) {
+            node.span = node.span.apply_mark(self.config.used_mark);
+            node.expr = self.fold_in_marking_phase(node.expr);
+        }
+
+        node
+    }
+}
+
+impl Fold<NamedExport> for Dce<'_> {
+    fn fold(&mut self, mut node: NamedExport) -> NamedExport {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        // Export only when it's required.
+        node.specifiers.retain(|s| match s {
+            ExportSpecifier::Namespace(s) => self.is_exported(&s.name.sym),
+            ExportSpecifier::Default(..) => self.is_exported(&js_word!("default")),
+            ExportSpecifier::Named(s) => {
+                self.is_exported(&s.exported.as_ref().unwrap_or_else(|| &s.orig).sym)
+            }
+        });
+
+        if !node.specifiers.is_empty() {
+            node.span = node.span.apply_mark(self.config.used_mark);
+            node.specifiers = self.fold_in_marking_phase(node.specifiers);
+        }
+
+        node
+    }
+}
+
+impl Fold<ExportDefaultDecl> for Dce<'_> {
+    fn fold(&mut self, mut node: ExportDefaultDecl) -> ExportDefaultDecl {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        // TODO: Export only when it's required. (i.e. check self.used_exports)
+
+        node.span = node.span.apply_mark(self.config.used_mark);
+        node.decl = self.fold_in_marking_phase(node.decl);
+
+        node
+    }
+}
+
+impl Fold<ExportAll> for Dce<'_> {
+    fn fold(&mut self, node: ExportAll) -> ExportAll {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        unimplemented!("dce: `export * from 'foo'`")
+    }
+}
+
+preserve!(TsImportEqualsDecl);
+preserve!(TsExportAssignment);
+preserve!(TsNamespaceExportDecl);

ecmascript/transforms/src/optimization/simplify/dce/side_effect.rs

@@ -0,0 +1,200 @@
+use super::Dce;
+use fxhash::FxHashSet;
+use swc_common::{Visit, VisitWith};
+use swc_ecma_ast::*;
+use swc_ecma_utils::{ident::IdentLike, ExprExt, Id};
+
+impl Dce<'_> {
+    pub fn should_include<T>(&mut self, node: &T) -> bool
+    where
+        T: for<'any> VisitWith<SideEffectVisitor<'any>>,
+    {
+        let mut v = SideEffectVisitor {
+            included: &mut self.included,
+            exports: self.config.used.as_ref().map(|v| &**v),
+            found: false,
+        };
+
+        node.visit_with(&mut v);
+
+        v.found
+    }
+}
+
+pub(super) struct SideEffectVisitor<'a> {
+    included: &'a mut FxHashSet<Id>,
+    exports: Option<&'a [Id]>,
+    found: bool,
+}
+
+impl SideEffectVisitor<'_> {
+    fn include(&self, i: &Id) -> bool {
+        let id = i.to_id();
+        if self.included.contains(&id) {
+            return true;
+        }
+
+        if let Some(exports) = self.exports {
+            if exports.contains(&id) {
+                return true;
+            }
+        }
+
+        false
+    }
+}
+
+impl Visit<Expr> for SideEffectVisitor<'_> {
+    fn visit(&mut self, node: &Expr) {
+        log::debug!("Visit<Expr>");
+
+        if self.found || node.is_pure_callee() {
+            return;
+        }
+
+        match node {
+            Expr::Lit(..) | Expr::PrivateName(..) | Expr::TsConstAssertion(..) => return,
+
+            _ => {}
+        }
+
+        node.visit_children(self)
+    }
+}
+
+impl Visit<AssignExpr> for SideEffectVisitor<'_> {
+    fn visit(&mut self, node: &AssignExpr) {
+        if self.found {
+            return;
+        }
+
+        node.left.visit_with(self);
+
+        match &*node.right {
+            Expr::Ident(..) => {
+                //TODO: Check for alias
+            }
+            right => right.visit_with(self),
+        }
+    }
+}
+
+impl Visit<MemberExpr> for SideEffectVisitor<'_> {
+    fn visit(&mut self, _: &MemberExpr) {
+        self.found = true;
+
+        //        if self.found {
+        //            return;
+        //        }
+
+        //        node.obj.visit_with(self);
+        //        if node.computed {
+        //            node.prop.visit_with(self);
+        //        }
+    }
+}
+
+impl Visit<Ident> for SideEffectVisitor<'_> {
+    fn visit(&mut self, node: &Ident) {
+        if self.found {
+            return;
+        }
+
+        self.found |= self.include(&node.to_id());
+    }
+}
+
+impl Visit<CallExpr> for SideEffectVisitor<'_> {
+    fn visit(&mut self, node: &CallExpr) {
+        if self.found {
+            return;
+        }
+
+        match node.callee {
+            ExprOrSuper::Expr(ref e) if e.is_pure_callee() => return,
+            _ => {}
+        }
+
+        self.found = true;
+    }
+}
+
+impl Visit<NewExpr> for SideEffectVisitor<'_> {
+    fn visit(&mut self, _: &NewExpr) {
+        if self.found {
+            return;
+        }
+
+        self.found = true;
+    }
+}
+
+impl Visit<ExprOrSpread> for SideEffectVisitor<'_> {
+    fn visit(&mut self, node: &ExprOrSpread) {
+        if self.found {
+            return;
+        }
+
+        if node.spread.is_some() {
+            self.found = true;
+        }
+
+        if !self.found {
+            node.expr.visit_with(self);
+        }
+    }
+}
+
+impl Visit<ReturnStmt> for SideEffectVisitor<'_> {
+    fn visit(&mut self, _: &ReturnStmt) {
+        self.found = true;
+    }
+}
+
+impl Visit<ThrowStmt> for SideEffectVisitor<'_> {
+    fn visit(&mut self, _: &ThrowStmt) {
+        self.found = true;
+    }
+}
+
+impl Visit<BreakStmt> for SideEffectVisitor<'_> {
+    fn visit(&mut self, _: &BreakStmt) {
+        self.found = true;
+    }
+}
+
+impl Visit<ContinueStmt> for SideEffectVisitor<'_> {
+    fn visit(&mut self, _: &ContinueStmt) {
+        self.found = true;
+    }
+}
+
+impl Visit<ForStmt> for SideEffectVisitor<'_> {
+    fn visit(&mut self, _: &ForStmt) {
+        self.found = true;
+    }
+}
+
+impl Visit<ForInStmt> for SideEffectVisitor<'_> {
+    fn visit(&mut self, _: &ForInStmt) {
+        self.found = true;
+    }
+}
+
+impl Visit<ForOfStmt> for SideEffectVisitor<'_> {
+    fn visit(&mut self, _: &ForOfStmt) {
+        self.found = true;
+    }
+}
+
+impl Visit<WhileStmt> for SideEffectVisitor<'_> {
+    fn visit(&mut self, _: &WhileStmt) {
+        self.found = true;
+    }
+}
+
+impl Visit<DoWhileStmt> for SideEffectVisitor<'_> {
+    fn visit(&mut self, _: &DoWhileStmt) {
+        self.found = true;
+    }
+}

ecmascript/transforms/src/optimization/simplify/dce/stmt.rs

@@ -0,0 +1,293 @@
+use super::Dce;
+use swc_common::{fold::FoldWith, Fold, Spanned};
+use swc_ecma_ast::*;
+
+impl Fold<ExprStmt> for Dce<'_> {
+    fn fold(&mut self, node: ExprStmt) -> ExprStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        if self.should_include(&node.expr) {
+            let stmt = ExprStmt {
+                span: node.span.apply_mark(self.config.used_mark),
+                expr: self.fold_in_marking_phase(node.expr),
+            };
+            return stmt;
+        }
+
+        node.fold_children(self)
+    }
+}
+
+impl Fold<BlockStmt> for Dce<'_> {
+    fn fold(&mut self, node: BlockStmt) -> BlockStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        let stmts = node.stmts.fold_with(self);
+
+        let mut span = node.span;
+        if stmts.iter().any(|stmt| self.is_marked(stmt.span())) {
+            span = span.apply_mark(self.config.used_mark);
+        }
+
+        BlockStmt { span, stmts }
+    }
+}
+
+impl Fold<IfStmt> for Dce<'_> {
+    fn fold(&mut self, node: IfStmt) -> IfStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        let mut node: IfStmt = node.fold_children(self);
+
+        if self.is_marked(node.test.span())
+            || self.is_marked(node.cons.span())
+            || self.is_marked(node.alt.span())
+        {
+            node.span = node.span.apply_mark(self.config.used_mark);
+
+            node.test = self.fold_in_marking_phase(node.test);
+            node.cons = self.fold_in_marking_phase(node.cons);
+            node.alt = self.fold_in_marking_phase(node.alt);
+        }
+
+        node
+    }
+}
+
+impl Fold<ReturnStmt> for Dce<'_> {
+    fn fold(&mut self, mut node: ReturnStmt) -> ReturnStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+        node.span = node.span.apply_mark(self.config.used_mark);
+
+        let mut node = node.fold_children(self);
+
+        if self.is_marked(node.arg.span()) {
+            node.arg = self.fold_in_marking_phase(node.arg)
+        }
+
+        node
+    }
+}
+
+impl Fold<ThrowStmt> for Dce<'_> {
+    fn fold(&mut self, mut node: ThrowStmt) -> ThrowStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+        node.span = node.span.apply_mark(self.config.used_mark);
+
+        let mut node = node.fold_children(self);
+
+        if self.is_marked(node.arg.span()) {
+            node.arg = self.fold_in_marking_phase(node.arg)
+        }
+
+        node
+    }
+}
+
+impl Fold<LabeledStmt> for Dce<'_> {
+    fn fold(&mut self, mut node: LabeledStmt) -> LabeledStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        node.body = node.body.fold_with(self);
+
+        if self.is_marked(node.body.span()) {
+            node.span = node.span.apply_mark(self.config.used_mark);
+            node.body = self.fold_in_marking_phase(node.body);
+        }
+
+        node
+    }
+}
+
+impl Fold<SwitchStmt> for Dce<'_> {
+    fn fold(&mut self, mut node: SwitchStmt) -> SwitchStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        node = node.fold_children(self);
+
+        // TODO: Handle fallthrough
+        //  Drop useless switch case.
+        //        node.cases.retain(|case| {
+        //            self.is_marked(case.span)
+        //        });
+
+        if self.is_marked(node.discriminant.span())
+            || node.cases.iter().any(|case| self.is_marked(case.span))
+        {
+            node.span = node.span.apply_mark(self.config.used_mark);
+            node.cases = self.fold_in_marking_phase(node.cases);
+        }
+
+        node
+    }
+}
+
+impl Fold<SwitchCase> for Dce<'_> {
+    fn fold(&mut self, mut node: SwitchCase) -> SwitchCase {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        node = node.fold_children(self);
+
+        if self.is_marked(node.test.span()) || node.cons.iter().any(|v| self.is_marked(v.span())) {
+            node.span = node.span.apply_mark(self.config.used_mark);
+
+            node.test = self.fold_in_marking_phase(node.test);
+            node.cons = self.fold_in_marking_phase(node.cons);
+        }
+
+        node
+    }
+}
+
+impl Fold<TryStmt> for Dce<'_> {
+    fn fold(&mut self, mut node: TryStmt) -> TryStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        node = node.fold_children(self);
+
+        if self.is_marked(node.block.span())
+            || self.is_marked(node.handler.span())
+            || self.is_marked(node.finalizer.span())
+        {
+            node.span = node.span.apply_mark(self.config.used_mark);
+
+            node.block = self.fold_in_marking_phase(node.block);
+            node.handler = self.fold_in_marking_phase(node.handler);
+            node.finalizer = self.fold_in_marking_phase(node.finalizer);
+        }
+
+        node
+    }
+}
+
+impl Fold<WhileStmt> for Dce<'_> {
+    fn fold(&mut self, mut node: WhileStmt) -> WhileStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        node = node.fold_children(self);
+
+        if self.is_marked(node.test.span()) || self.is_marked(node.body.span()) {
+            node.span = node.span.apply_mark(self.config.used_mark);
+
+            node.test = self.fold_in_marking_phase(node.test);
+            node.body = self.fold_in_marking_phase(node.body);
+        }
+
+        node
+    }
+}
+
+impl Fold<DoWhileStmt> for Dce<'_> {
+    fn fold(&mut self, mut node: DoWhileStmt) -> DoWhileStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        node = node.fold_children(self);
+
+        if self.is_marked(node.test.span()) || self.is_marked(node.body.span()) {
+            node.span = node.span.apply_mark(self.config.used_mark);
+
+            node.test = self.fold_in_marking_phase(node.test);
+            node.body = self.fold_in_marking_phase(node.body);
+        }
+
+        node
+    }
+}
+
+impl Fold<ForStmt> for Dce<'_> {
+    fn fold(&mut self, mut node: ForStmt) -> ForStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        node = node.fold_children(self);
+
+        if self.is_marked(node.init.span())
+            || self.is_marked(node.test.span())
+            || self.is_marked(node.update.span())
+            || self.is_marked(node.body.span())
+        {
+            node.span = node.span.apply_mark(self.config.used_mark);
+
+            node.test = self.fold_in_marking_phase(node.test);
+            node.init = self.fold_in_marking_phase(node.init);
+            node.update = self.fold_in_marking_phase(node.update);
+            node.body = self.fold_in_marking_phase(node.body);
+        }
+
+        node
+    }
+}
+
+impl Fold<ForInStmt> for Dce<'_> {
+    fn fold(&mut self, mut node: ForInStmt) -> ForInStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        node = node.fold_children(self);
+
+        if self.is_marked(node.left.span())
+            || self.is_marked(node.right.span())
+            || self.is_marked(node.body.span())
+        {
+            node.span = node.span.apply_mark(self.config.used_mark);
+
+            node.left = self.fold_in_marking_phase(node.left);
+            node.right = self.fold_in_marking_phase(node.right);
+            node.body = self.fold_in_marking_phase(node.body);
+        }
+
+        node
+    }
+}
+
+impl Fold<ForOfStmt> for Dce<'_> {
+    fn fold(&mut self, mut node: ForOfStmt) -> ForOfStmt {
+        if self.is_marked(node.span) {
+            return node;
+        }
+
+        node = node.fold_children(self);
+
+        if self.is_marked(node.left.span())
+            || self.is_marked(node.right.span())
+            || self.is_marked(node.body.span())
+        {
+            node.span = node.span.apply_mark(self.config.used_mark);
+
+            node.left = self.fold_in_marking_phase(node.left);
+            node.right = self.fold_in_marking_phase(node.right);
+            node.body = self.fold_in_marking_phase(node.body);
+        }
+
+        node
+    }
+}
+
+preserve!(DebuggerStmt);
+preserve!(WithStmt);
+preserve!(BreakStmt);
+preserve!(ContinueStmt);

ecmascript/transforms/src/optimization/simplify/expr/tests.rs

@@ -3,7 +3,7 @@ use super::SimplifyExpr;
 fn fold(src: &str, expected: &str) {
     test_transform!(
         ::swc_ecma_parser::Syntax::default(),
-        |_| SimplifyExpr,
+        |_| SimplifyExpr { changed: false },
         src,
         expected,
         true
@@ -15,6 +15,11 @@ fn fold_same(s: &str) {
     fold(s, s)
 }
 
+#[test]
+fn regex() {
+    fold("/ab/?x=1:x=2", "x=1");
+}
+
 #[test]
 fn object() {
     fold("!({a:foo()});", "foo(), false;");

ecmascript/transforms/src/optimization/simplify/inlining/mod.rs

@@ -0,0 +1,850 @@
+use self::scope::{Scope, ScopeKind, VarType};
+use crate::{pass::RepeatedJsPass, scope::IdentType};
+use std::borrow::Cow;
+use swc_common::{
+    pass::{CompilerPass, Repeated},
+    Fold, FoldWith, Visit, VisitWith,
+};
+use swc_ecma_ast::*;
+use swc_ecma_utils::{contains_this_expr, find_ids, ident::IdentLike, undefined, Id};
+
+mod scope;
+
+#[derive(Debug, Default)]
+pub struct Config {}
+
+/// Note: this pass assumes that resolver is invoked before the pass.
+///
+/// As swc focuses on reducing gzipped file size, all strings are inlined.
+///
+///
+/// # TODOs
+///
+///  - Handling of `void 0`
+///  - Properly handle binary expressions.
+///  - Track variables access by a function
+///
+/// Currently all functions are treated as a black box, and all the pass gives
+/// up inlining variables across a function call or a constructor call.
+pub fn inlining(_: Config) -> impl RepeatedJsPass + 'static {
+    Inlining {
+        phase: Phase::Analysis,
+        is_first_run: true,
+        changed: false,
+        scope: Default::default(),
+        var_decl_kind: VarDeclKind::Var,
+        ident_type: IdentType::Ref,
+        pat_mode: PatFoldingMode::VarDecl,
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Phase {
+    Analysis,
+    Inlining,
+}
+
+impl CompilerPass for Inlining<'_> {
+    fn name() -> Cow<'static, str> {
+        Cow::Borrowed("inlining")
+    }
+}
+
+impl Repeated for Inlining<'_> {
+    fn changed(&self) -> bool {
+        self.changed
+    }
+
+    fn reset(&mut self) {
+        self.changed = false;
+        self.is_first_run = false;
+    }
+}
+
+struct Inlining<'a> {
+    phase: Phase,
+    is_first_run: bool,
+    changed: bool,
+    scope: Scope<'a>,
+    var_decl_kind: VarDeclKind,
+    ident_type: IdentType,
+    pat_mode: PatFoldingMode,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum PatFoldingMode {
+    Assign,
+    Param,
+    CatchParam,
+    VarDecl,
+}
+
+impl Inlining<'_> {
+    fn fold_with_child<T>(&mut self, kind: ScopeKind, node: T) -> T
+    where
+        T: 'static + for<'any> FoldWith<Inlining<'any>>,
+    {
+        self.with_child(kind, node, |child, node| node.fold_children(child))
+    }
+}
+
+impl Fold<Vec<ModuleItem>> for Inlining<'_> {
+    fn fold(&mut self, mut items: Vec<ModuleItem>) -> Vec<ModuleItem> {
+        let old_phase = self.phase;
+
+        self.phase = Phase::Analysis;
+        items = items.fold_children(self);
+
+        log::debug!("Switching to Inlining phase");
+
+        // Inline
+        self.phase = Phase::Inlining;
+        items = items.fold_children(self);
+
+        self.phase = old_phase;
+
+        items
+    }
+}
+
+impl Fold<Vec<Stmt>> for Inlining<'_> {
+    fn fold(&mut self, mut items: Vec<Stmt>) -> Vec<Stmt> {
+        let old_phase = self.phase;
+
+        match old_phase {
+            Phase::Analysis => {
+                items = items.fold_children(self);
+            }
+            Phase::Inlining => {
+                self.phase = Phase::Analysis;
+                items = items.fold_children(self);
+
+                // Inline
+                self.phase = Phase::Inlining;
+                items = items.fold_children(self);
+
+                self.phase = old_phase
+            }
+        }
+
+        items
+    }
+}
+
+impl Fold<VarDecl> for Inlining<'_> {
+    fn fold(&mut self, decl: VarDecl) -> VarDecl {
+        self.var_decl_kind = decl.kind;
+
+        decl.fold_children(self)
+    }
+}
+
+impl Fold<VarDeclarator> for Inlining<'_> {
+    fn fold(&mut self, mut node: VarDeclarator) -> VarDeclarator {
+        let kind = VarType::Var(self.var_decl_kind);
+        node.init = node.init.fold_with(self);
+
+        self.pat_mode = PatFoldingMode::VarDecl;
+
+        match self.phase {
+            Phase::Analysis => match node.name {
+                Pat::Ident(ref name) => {
+                    //
+                    match &node.init {
+                        None => {
+                            if self.var_decl_kind != VarDeclKind::Const {
+                                self.declare(name.to_id(), None, true, kind);
+                            }
+                        }
+
+                        // Constants
+                        Some(box e @ Expr::Lit(..)) | Some(box e @ Expr::Ident(..))
+                            if self.var_decl_kind == VarDeclKind::Const =>
+                        {
+                            if self.is_first_run {
+                                self.scope.constants.insert(name.to_id(), Some(e.clone()));
+                            }
+                        }
+                        Some(..) if self.var_decl_kind == VarDeclKind::Const => {
+                            if self.is_first_run {
+                                self.scope.constants.insert(name.to_id(), None);
+                            }
+                        }
+
+                        // Bindings
+                        Some(box e @ Expr::Lit(..)) | Some(box e @ Expr::Ident(..)) => {
+                            self.declare(name.to_id(), Some(Cow::Borrowed(&e)), false, kind);
+
+                            if self.scope.is_inline_prevented(&e) {
+                                self.scope.prevent_inline(&name.to_id());
+                            }
+                        }
+                        Some(ref e) => {
+                            if self.var_decl_kind != VarDeclKind::Const {
+                                self.declare(name.to_id(), Some(Cow::Borrowed(&e)), false, kind);
+
+                                if contains_this_expr(&node.init) {
+                                    self.scope.prevent_inline(&name.to_id());
+                                    return node;
+                                }
+                            }
+                        }
+                    }
+                }
+                _ => {}
+            },
+            Phase::Inlining => {
+                match node.name {
+                    Pat::Ident(ref name) => {
+                        if self.var_decl_kind != VarDeclKind::Const {
+                            let id = name.to_id();
+
+                            log::trace!("Trying to optimize variable declaration: {:?}", id);
+
+                            if self.scope.is_inline_prevented(&Expr::Ident(name.clone()))
+                                || !self
+                                    .scope
+                                    .has_same_this(&id, node.init.as_ref().map(|v| &**v))
+                            {
+                                log::trace!("Inline is prevented for {:?}", id);
+                                return node;
+                            }
+
+                            let init = node.init.take().fold_with(self);
+                            log::trace!("\tInit: {:?}", init);
+
+                            match init {
+                                Some(box Expr::Ident(ref ri)) => {
+                                    self.declare(
+                                        name.to_id(),
+                                        Some(Cow::Owned(Expr::Ident(ri.clone()))),
+                                        false,
+                                        kind,
+                                    );
+                                }
+
+                                _ => {}
+                            }
+
+                            match init {
+                                Some(ref e) => {
+                                    if self.scope.is_inline_prevented(&e) {
+                                        log::trace!(
+                                            "Inlining is not possible as inline of the \
+                                             initialization was prevented"
+                                        );
+                                        node.init = init;
+                                        self.scope.prevent_inline(&name.to_id());
+                                        return node;
+                                    }
+                                }
+                                _ => {}
+                            }
+
+                            let e = match init {
+                                None => None,
+                                Some(box e @ Expr::Lit(..)) | Some(box e @ Expr::Ident(..)) => {
+                                    Some(e)
+                                }
+                                Some(box e) => {
+                                    if self.scope.is_inline_prevented(&Expr::Ident(name.clone())) {
+                                        node.init = Some(box e);
+                                        return node;
+                                    }
+
+                                    if let Some(cnt) = self.scope.read_cnt(&name.to_id()) {
+                                        if cnt == 1 {
+                                            Some(e)
+                                        } else {
+                                            node.init = Some(box e);
+                                            return node;
+                                        }
+                                    } else {
+                                        node.init = Some(box e);
+                                        return node;
+                                    }
+                                }
+                            };
+
+                            // log::trace!("({}): Inserting {:?}", self.scope.depth(),
+                            // name.to_id());
+
+                            self.declare(name.to_id(), e.map(Cow::Owned), false, kind);
+
+                            return node;
+                        }
+                    }
+                    _ => {}
+                }
+            }
+        }
+
+        node.name = node.name.fold_with(self);
+
+        node
+    }
+}
+
+impl Fold<BlockStmt> for Inlining<'_> {
+    fn fold(&mut self, node: BlockStmt) -> BlockStmt {
+        self.fold_with_child(ScopeKind::Block, node)
+    }
+}
+
+impl Fold<ArrowExpr> for Inlining<'_> {
+    fn fold(&mut self, node: ArrowExpr) -> ArrowExpr {
+        self.fold_with_child(ScopeKind::Fn { named: false }, node)
+    }
+}
+
+impl Fold<Function> for Inlining<'_> {
+    fn fold(&mut self, node: Function) -> Function {
+        self.with_child(
+            ScopeKind::Fn { named: false },
+            node,
+            move |child, mut node| {
+                child.pat_mode = PatFoldingMode::Param;
+                node.params = node.params.fold_with(child);
+                node.body = match node.body {
+                    None => None,
+                    Some(v) => Some(v.fold_children(child)),
+                };
+
+                node
+            },
+        )
+    }
+}
+
+impl Fold<FnDecl> for Inlining<'_> {
+    fn fold(&mut self, node: FnDecl) -> FnDecl {
+        if self.phase == Phase::Analysis {
+            self.declare(
+                node.ident.to_id(),
+                None,
+                true,
+                VarType::Var(VarDeclKind::Var),
+            );
+        }
+
+        let function = node.function;
+
+        let function = self.with_child(
+            ScopeKind::Fn { named: true },
+            function,
+            |child, mut node| {
+                child.pat_mode = PatFoldingMode::Param;
+                node.params = node.params.fold_with(child);
+                node.body = match node.body {
+                    None => None,
+                    Some(v) => Some(v.fold_children(child)),
+                };
+
+                node
+            },
+        );
+        FnDecl { function, ..node }
+    }
+}
+
+impl Fold<FnExpr> for Inlining<'_> {
+    fn fold(&mut self, node: FnExpr) -> FnExpr {
+        if let Some(ref ident) = node.ident {
+            self.scope.add_write(&ident.to_id(), true);
+        }
+
+        FnExpr {
+            function: node.function.fold_with(self),
+            ..node
+        }
+    }
+}
+
+impl Fold<IfStmt> for Inlining<'_> {
+    fn fold(&mut self, mut node: IfStmt) -> IfStmt {
+        node.test = node.test.fold_with(self);
+
+        node.cons = self.fold_with_child(ScopeKind::Cond, node.cons);
+        node.alt = self.fold_with_child(ScopeKind::Cond, node.alt);
+
+        node
+    }
+}
+
+impl Fold<SwitchCase> for Inlining<'_> {
+    fn fold(&mut self, node: SwitchCase) -> SwitchCase {
+        self.fold_with_child(ScopeKind::Block, node)
+    }
+}
+
+impl Fold<CatchClause> for Inlining<'_> {
+    fn fold(&mut self, node: CatchClause) -> CatchClause {
+        self.with_child(ScopeKind::Block, node, move |child, mut node| {
+            child.pat_mode = PatFoldingMode::CatchParam;
+            node.param = node.param.fold_with(child);
+            match child.phase {
+                Phase::Analysis => {
+                    let ids: Vec<Id> = find_ids(&node.param);
+                    for id in ids {
+                        child.scope.prevent_inline(&id);
+                    }
+                }
+                Phase::Inlining => {}
+            }
+
+            node.body = node.body.fold_with(child);
+
+            node
+        })
+    }
+}
+
+impl Fold<CallExpr> for Inlining<'_> {
+    fn fold(&mut self, mut node: CallExpr) -> CallExpr {
+        node.callee = node.callee.fold_with(self);
+
+        if self.phase == Phase::Analysis {
+            match node.callee {
+                ExprOrSuper::Expr(ref callee) => {
+                    self.scope.mark_this_sensitive(&callee);
+                }
+
+                _ => {}
+            }
+        }
+
+        node.args = node.args.fold_with(self);
+
+        self.scope.store_inline_barrier(self.phase);
+
+        node
+    }
+}
+
+impl Fold<NewExpr> for Inlining<'_> {
+    fn fold(&mut self, mut node: NewExpr) -> NewExpr {
+        node.callee = node.callee.fold_with(self);
+        if self.phase == Phase::Analysis {
+            self.scope.mark_this_sensitive(&node.callee);
+        }
+
+        node.args = node.args.fold_with(self);
+
+        self.scope.store_inline_barrier(self.phase);
+
+        node
+    }
+}
+
+impl Fold<AssignExpr> for Inlining<'_> {
+    fn fold(&mut self, e: AssignExpr) -> AssignExpr {
+        log::trace!("{:?}; Fold<AssignExpr>", self.phase);
+        self.pat_mode = PatFoldingMode::Assign;
+        let e = AssignExpr {
+            left: match e.left {
+                PatOrExpr::Expr(left) | PatOrExpr::Pat(box Pat::Expr(left)) => {
+                    //
+                    match *left {
+                        Expr::Member(ref left) => {
+                            log::trace!("Assign to member expression!");
+                            let mut v = IdentListVisitor {
+                                scope: &mut self.scope,
+                            };
+
+                            left.visit_with(&mut v);
+                            e.right.visit_with(&mut v);
+                        }
+
+                        _ => {}
+                    }
+
+                    PatOrExpr::Expr(left)
+                }
+                PatOrExpr::Pat(p) => PatOrExpr::Pat(p.fold_with(self)),
+            },
+            right: e.right.fold_with(self),
+            ..e
+        };
+
+        match e.op {
+            op!("=") => {}
+            _ => {
+                let mut v = IdentListVisitor {
+                    scope: &mut self.scope,
+                };
+
+                e.left.visit_with(&mut v);
+                e.right.visit_with(&mut v)
+            }
+        }
+
+        if self.scope.is_inline_prevented(&e.right) {
+            // Prevent inline for lhd
+            let ids: Vec<Id> = find_ids(&e.left);
+            for id in ids {
+                self.scope.prevent_inline(&id);
+            }
+            return e;
+        }
+
+        match *e.right {
+            Expr::Lit(..) | Expr::Ident(..) => {
+                //
+                match e.left {
+                    PatOrExpr::Pat(box Pat::Ident(ref i))
+                    | PatOrExpr::Expr(box Expr::Ident(ref i)) => {
+                        let id = i.to_id();
+                        self.scope.add_write(&id, false);
+
+                        if let Some(var) = self.scope.find_binding(&id) {
+                            if !var.is_inline_prevented() {
+                                *var.value.borrow_mut() = Some(*e.right.clone());
+                            }
+                        }
+                    }
+                    _ => {}
+                }
+            }
+
+            _ => {}
+        }
+
+        e
+    }
+}
+
+impl Fold<MemberExpr> for Inlining<'_> {
+    fn fold(&mut self, mut e: MemberExpr) -> MemberExpr {
+        e.obj = e.obj.fold_with(self);
+        if e.computed {
+            e.prop = e.prop.fold_with(self);
+        }
+
+        e
+    }
+}
+
+impl Fold<Expr> for Inlining<'_> {
+    fn fold(&mut self, node: Expr) -> Expr {
+        let node: Expr = node.fold_children(self);
+
+        // Codes like
+        //
+        //      var y;
+        //      y = x;
+        //      use(y)
+        //
+        //  should be transformed to
+        //
+        //      var y;
+        //      x;
+        //      use(x)
+        //
+        // We cannot know if this is possible while analysis phase
+        if self.phase == Phase::Inlining {
+            match node {
+                Expr::Assign(e @ AssignExpr { op: op!("="), .. }) => {
+                    match e.left {
+                        PatOrExpr::Pat(box Pat::Ident(ref i))
+                        | PatOrExpr::Expr(box Expr::Ident(ref i)) => {
+                            if let Some(var) = self.scope.find_binding_from_current(&i.to_id()) {
+                                if var.is_undefined.get() && !var.is_inline_prevented() {
+                                    if !self.scope.is_inline_prevented(&e.right) {
+                                        *var.value.borrow_mut() = Some(*e.right.clone());
+                                        var.is_undefined.set(false);
+                                        return *e.right;
+                                    }
+                                }
+                            }
+                        }
+                        _ => {}
+                    }
+
+                    return Expr::Assign(e);
+                }
+
+                _ => {}
+            }
+        }
+
+        match node {
+            Expr::Ident(ref i) => {
+                let id = i.to_id();
+                if self.is_first_run {
+                    if let Some(expr) = self.scope.find_constant(&id) {
+                        self.changed = true;
+                        return expr.clone().fold_with(self);
+                    }
+                }
+
+                match self.phase {
+                    Phase::Analysis => {
+                        self.scope.add_read(&id);
+                    }
+                    Phase::Inlining => {
+                        log::trace!("Trying to inline: {:?}", id);
+                        let expr = if let Some(var) = self.scope.find_binding(&id) {
+                            log::trace!("VarInfo: {:?}", var);
+                            if !var.is_inline_prevented() {
+                                let expr = var.value.borrow();
+
+                                if let Some(expr) = &*expr {
+                                    if node != *expr {
+                                        self.changed = true;
+                                    }
+
+                                    Some(expr.clone())
+                                } else {
+                                    if var.is_undefined.get() {
+                                        return *undefined(i.span);
+                                    } else {
+                                        log::trace!("Not a cheap expression");
+                                        None
+                                    }
+                                }
+                            } else {
+                                log::trace!("Inlining is prevented");
+                                None
+                            }
+                        } else {
+                            None
+                        };
+
+                        if let Some(expr) = expr {
+                            return expr;
+                        }
+                    }
+                }
+            }
+
+            _ => {}
+        }
+
+        node
+    }
+}
+
+impl Fold<UpdateExpr> for Inlining<'_> {
+    fn fold(&mut self, node: UpdateExpr) -> UpdateExpr {
+        let mut v = IdentListVisitor {
+            scope: &mut self.scope,
+        };
+
+        node.arg.visit_with(&mut v);
+        node
+    }
+}
+
+impl Fold<UnaryExpr> for Inlining<'_> {
+    fn fold(&mut self, node: UnaryExpr) -> UnaryExpr {
+        match node.op {
+            op!("delete") => {
+                let mut v = IdentListVisitor {
+                    scope: &mut self.scope,
+                };
+
+                node.arg.visit_with(&mut v);
+                return node;
+            }
+
+            _ => {}
+        }
+
+        node.fold_children(self)
+    }
+}
+
+impl Fold<Pat> for Inlining<'_> {
+    fn fold(&mut self, node: Pat) -> Pat {
+        let node: Pat = node.fold_children(self);
+
+        match node {
+            Pat::Ident(ref i) => match self.pat_mode {
+                PatFoldingMode::Param => {
+                    self.declare(
+                        i.to_id(),
+                        Some(Cow::Owned(Expr::Ident(i.clone()))),
+                        false,
+                        VarType::Param,
+                    );
+                }
+                PatFoldingMode::CatchParam => {
+                    self.declare(
+                        i.to_id(),
+                        Some(Cow::Owned(Expr::Ident(i.clone()))),
+                        false,
+                        VarType::Var(VarDeclKind::Var),
+                    );
+                }
+                PatFoldingMode::VarDecl => {}
+                PatFoldingMode::Assign => {
+                    if let Some(..) = self.scope.find_binding_from_current(&i.to_id()) {
+                    } else {
+                        self.scope.add_write(&i.to_id(), false);
+                    }
+                }
+            },
+
+            _ => {}
+        }
+
+        node
+    }
+}
+
+impl Fold<ForInStmt> for Inlining<'_> {
+    fn fold(&mut self, mut node: ForInStmt) -> ForInStmt {
+        self.pat_mode = PatFoldingMode::Param;
+        node.left = node.left.fold_with(self);
+
+        {
+            node.left.visit_with(&mut IdentListVisitor {
+                scope: &mut self.scope,
+            });
+        }
+
+        {
+            node.right.visit_with(&mut IdentListVisitor {
+                scope: &mut self.scope,
+            });
+        }
+
+        node.right = node.right.fold_with(self);
+        node.body = self.fold_with_child(ScopeKind::Loop, node.body);
+
+        node
+    }
+}
+
+impl Fold<ForOfStmt> for Inlining<'_> {
+    fn fold(&mut self, mut node: ForOfStmt) -> ForOfStmt {
+        self.pat_mode = PatFoldingMode::Param;
+        node.left = node.left.fold_with(self);
+
+        {
+            node.left.visit_with(&mut IdentListVisitor {
+                scope: &mut self.scope,
+            });
+        }
+        {
+            node.right.visit_with(&mut IdentListVisitor {
+                scope: &mut self.scope,
+            });
+        }
+
+        node.right = node.right.fold_with(self);
+        node.body = self.fold_with_child(ScopeKind::Loop, node.body);
+
+        node
+    }
+}
+
+impl Fold<ForStmt> for Inlining<'_> {
+    fn fold(&mut self, mut node: ForStmt) -> ForStmt {
+        node.init = node.init.fold_with(self);
+
+        {
+            node.init.visit_with(&mut IdentListVisitor {
+                scope: &mut self.scope,
+            });
+        }
+        {
+            node.test.visit_with(&mut IdentListVisitor {
+                scope: &mut self.scope,
+            });
+        }
+        {
+            node.update.visit_with(&mut IdentListVisitor {
+                scope: &mut self.scope,
+            });
+        }
+
+        node.test = node.test.fold_with(self);
+        node.update = node.update.fold_with(self);
+        node.body = self.fold_with_child(ScopeKind::Loop, node.body);
+
+        if node.init.is_none() && node.test.is_none() && node.update.is_none() {
+            self.scope.store_inline_barrier(self.phase);
+        }
+
+        node
+    }
+}
+
+impl Fold<WhileStmt> for Inlining<'_> {
+    fn fold(&mut self, mut node: WhileStmt) -> WhileStmt {
+        {
+            node.test.visit_with(&mut IdentListVisitor {
+                scope: &mut self.scope,
+            });
+        }
+
+        node.test = node.test.fold_with(self);
+        node.body = self.fold_with_child(ScopeKind::Loop, node.body);
+
+        node
+    }
+}
+
+impl Fold<DoWhileStmt> for Inlining<'_> {
+    fn fold(&mut self, mut node: DoWhileStmt) -> DoWhileStmt {
+        {
+            node.test.visit_with(&mut IdentListVisitor {
+                scope: &mut self.scope,
+            });
+        }
+
+        node.test = node.test.fold_with(self);
+        node.body = self.fold_with_child(ScopeKind::Loop, node.body);
+
+        node
+    }
+}
+
+impl Fold<BinExpr> for Inlining<'_> {
+    fn fold(&mut self, node: BinExpr) -> BinExpr {
+        match node.op {
+            op!("&&") | op!("||") => BinExpr {
+                left: node.left.fold_with(self),
+                ..node
+            },
+            _ => node.fold_children(self),
+        }
+    }
+}
+
+impl Fold<TryStmt> for Inlining<'_> {
+    fn fold(&mut self, node: TryStmt) -> TryStmt {
+        node.block.visit_with(&mut IdentListVisitor {
+            scope: &mut self.scope,
+        });
+
+        TryStmt {
+            // TODO:
+            //            block: node.block.fold_with(self),
+            handler: node.handler.fold_with(self),
+            ..node
+        }
+    }
+}
+
+#[derive(Debug)]
+struct IdentListVisitor<'a, 'b> {
+    scope: &'a mut Scope<'b>,
+}
+
+impl Visit<MemberExpr> for IdentListVisitor<'_, '_> {
+    fn visit(&mut self, node: &MemberExpr) {
+        node.obj.visit_with(self);
+
+        if node.computed {
+            node.prop.visit_with(self);
+        }
+    }
+}
+
+impl Visit<Ident> for IdentListVisitor<'_, '_> {
+    fn visit(&mut self, node: &Ident) {
+        self.scope.add_write(&node.to_id(), true);
+    }
+}

ecmascript/transforms/src/optimization/simplify/inlining/scope.rs

@@ -0,0 +1,675 @@
+use super::{Inlining, Phase};
+use fxhash::{FxBuildHasher, FxHashMap, FxHashSet};
+use indexmap::map::{Entry, IndexMap};
+use std::{
+    borrow::Cow,
+    cell::{Cell, RefCell},
+    collections::VecDeque,
+};
+use swc_atoms::js_word;
+use swc_ecma_ast::*;
+use swc_ecma_utils::{ident::IdentLike, Id};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ScopeKind {
+    /// If / Switch
+    Cond,
+    Loop,
+    Block,
+    Fn {
+        named: bool,
+    },
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(super) enum VarType {
+    Param,
+    Var(VarDeclKind),
+}
+
+impl Default for ScopeKind {
+    fn default() -> Self {
+        Self::Fn { named: false }
+    }
+}
+
+impl Inlining<'_> {
+    pub(super) fn with_child<F, T>(&mut self, kind: ScopeKind, node: T, op: F) -> T
+    where
+        F: for<'any> FnOnce(&mut Inlining<'any>, T) -> T,
+    {
+        let (node, unresolved_usages, bindings) = {
+            let mut child = Inlining {
+                phase: self.phase,
+                is_first_run: self.is_first_run,
+                changed: false,
+                scope: Scope::new(Some(&self.scope), kind),
+                var_decl_kind: VarDeclKind::Var,
+                ident_type: self.ident_type,
+                pat_mode: self.pat_mode,
+            };
+
+            let node = op(&mut child, node);
+
+            self.changed |= child.changed;
+
+            (node, child.scope.unresolved_usages, child.scope.bindings)
+        };
+
+        log::trace!("propagating variables");
+
+        self.scope.unresolved_usages.extend(unresolved_usages);
+
+        if match kind {
+            ScopeKind::Fn { .. } => false,
+            _ => true,
+        } {
+            let v = bindings;
+
+            for (id, v) in v.into_iter().filter_map(|(id, v)| {
+                if v.kind == VarType::Var(VarDeclKind::Var) {
+                    Some((id, v))
+                } else {
+                    None
+                }
+            }) {
+                let v: VarInfo = v;
+
+                log::debug!("Hoisting a variable {:?}", id);
+
+                if self.scope.unresolved_usages.contains(&id) {
+                    v.inline_prevented.set(true)
+                }
+
+                v.hoisted.set(true);
+
+                *v.value.borrow_mut() = None;
+                v.is_undefined.set(false);
+                self.scope.bindings.insert(id, v);
+            }
+        }
+
+        node
+    }
+
+    /// Note: this method stores the value only if init is [Cow::Owned] or it's
+    /// [Expr::Ident] or [Expr::Lit].
+    pub(super) fn declare(
+        &mut self,
+        id: Id,
+        init: Option<Cow<Expr>>,
+        is_change: bool,
+        kind: VarType,
+    ) {
+        log::trace!(
+            "({}, {:?}) declare({})",
+            self.scope.depth(),
+            self.phase,
+            id.0
+        );
+
+        let init = init.map(|cow| match cow {
+            Cow::Owned(v) => Cow::Owned(v),
+            Cow::Borrowed(b) => match b {
+                Expr::Ident(..) | Expr::Lit(..) => Cow::Owned(b.clone()),
+                _ => Cow::Borrowed(b),
+            },
+        });
+
+        let is_undefined = self.var_decl_kind == VarDeclKind::Var
+            && !is_change
+            && init.is_none()
+            && self.phase == Phase::Inlining;
+
+        let mut alias_of = None;
+
+        let value_idx = match init.as_ref().map(|v| &**v) {
+            Some(&Expr::Ident(ref vi)) => {
+                if let Some((value_idx, value_var)) = self.scope.idx_val(&vi.to_id()) {
+                    alias_of = Some(value_var.kind);
+                    Some((value_idx, vi.to_id()))
+                } else {
+                    None
+                }
+            }
+            _ => None,
+        };
+
+        let is_inline_prevented = self.scope.should_prevent_inline_because_of_scope(&id)
+            || match init {
+                Some(ref e) => self.scope.is_inline_prevented(&e),
+                _ => false,
+            };
+
+        if is_inline_prevented {
+            log::trace!("\tdeclare: Inline prevented: {:?}", id)
+        }
+        if is_undefined {
+            log::trace!("\tdeclare: {:?} is undefined", id);
+        }
+
+        let idx = match self.scope.bindings.entry(id.clone()) {
+            Entry::Occupied(mut e) => {
+                e.get().is_undefined.set(is_undefined);
+                e.get().read_cnt.set(0);
+                e.get().read_from_nested_scope.set(false);
+
+                match init {
+                    Some(Cow::Owned(v)) => e.get_mut().value = RefCell::new(Some(v)),
+                    None => e.get_mut().value = RefCell::new(None),
+                    _ => {}
+                }
+
+                e.get().inline_prevented.set(is_inline_prevented);
+                e.index()
+            }
+            Entry::Vacant(e) => {
+                let idx = e.index();
+                e.insert(VarInfo {
+                    kind,
+                    alias_of,
+                    read_from_nested_scope: Cell::new(false),
+                    read_cnt: Cell::new(0),
+                    inline_prevented: Cell::new(is_inline_prevented),
+                    is_undefined: Cell::new(is_undefined),
+                    value: RefCell::new(match init {
+                        Some(Cow::Owned(v)) => Some(v),
+                        _ => None,
+                    }),
+                    this_sensitive: Cell::new(false),
+                    hoisted: Cell::new(false),
+                });
+                idx
+            }
+        };
+
+        {
+            let mut cur = Some(&self.scope);
+            while let Some(scope) = cur {
+                if let ScopeKind::Fn { .. } = scope.kind {
+                    break;
+                }
+
+                if scope.kind == ScopeKind::Loop {
+                    log::debug!("preventing inline as it's declared in a loop");
+                    self.scope.prevent_inline(&id);
+                    break;
+                }
+
+                cur = scope.parent;
+            }
+        }
+
+        //
+        let barrier_works = match kind {
+            VarType::Param => false,
+            _ if alias_of == Some(VarType::Param) => false,
+            _ => true,
+        };
+
+        if barrier_works {
+            if let Some((value_idx, vi)) = value_idx {
+                log::trace!("\tdeclare: {} -> {}", idx, value_idx);
+
+                let barrier_exists = (|| {
+                    for &blocker in self.scope.inline_barriers.borrow().iter() {
+                        if value_idx <= blocker && blocker <= idx {
+                            return true;
+                        } else if idx <= blocker && blocker <= value_idx {
+                            return true;
+                        }
+                    }
+
+                    false
+                })();
+
+                if value_idx > idx || barrier_exists {
+                    log::trace!("Variable use before declaration: {:?}", id);
+                    self.scope.prevent_inline(&id);
+                    self.scope.prevent_inline(&vi)
+                }
+            } else {
+                log::trace!("\tdeclare: value idx is none");
+            }
+        }
+    }
+}
+
+#[derive(Debug, Default)]
+pub(super) struct Scope<'a> {
+    pub parent: Option<&'a Scope<'a>>,
+    pub kind: ScopeKind,
+
+    inline_barriers: RefCell<VecDeque<usize>>,
+    bindings: IndexMap<Id, VarInfo, FxBuildHasher>,
+    unresolved_usages: FxHashSet<Id>,
+
+    /// Simple optimization. We don't need complex scope analysis.
+    pub constants: FxHashMap<Id, Option<Expr>>,
+}
+
+impl<'a> Scope<'a> {
+    pub fn new(parent: Option<&'a Scope<'a>>, kind: ScopeKind) -> Self {
+        Self {
+            parent,
+            kind,
+            ..Default::default()
+        }
+    }
+
+    pub fn depth(&self) -> usize {
+        match self.parent {
+            None => 0,
+            Some(p) => p.depth() + 1,
+        }
+    }
+
+    fn should_prevent_inline_because_of_scope(&self, id: &Id) -> bool {
+        if self.unresolved_usages.contains(id) {
+            return true;
+        }
+
+        match self.parent {
+            None => false,
+            Some(p) => {
+                if p.should_prevent_inline_because_of_scope(id) {
+                    return true;
+                }
+
+                if let Some(v) = p.find_binding(id) {
+                    if v.hoisted.get() && v.is_inline_prevented() {
+                        return true;
+                    }
+                }
+
+                false
+            }
+        }
+    }
+
+    /// True if the returned scope is self
+    fn scope_for(&self, id: &Id) -> (&Scope, bool) {
+        if let Some(..) = self.constants.get(id) {
+            return (self, true);
+        }
+        if let Some(..) = self.find_binding_from_current(id) {
+            return (self, true);
+        }
+
+        match self.parent {
+            None => (self, true),
+            Some(ref p) => {
+                let (s, _) = p.scope_for(id);
+                (s, false)
+            }
+        }
+    }
+
+    pub fn read_cnt(&self, id: &Id) -> Option<usize> {
+        if let Some(var) = self.find_binding(id) {
+            return Some(var.read_cnt.get());
+        }
+
+        None
+    }
+
+    fn read_prevents_inlining(&self, id: &Id) -> bool {
+        log::trace!("read_prevents_inlining({:?})", id);
+
+        if let Some(v) = self.find_binding(id) {
+            match v.kind {
+                // Reading parameter is ok.
+                VarType::Param => return false,
+                VarType::Var(VarDeclKind::Let) | VarType::Var(VarDeclKind::Const) => return false,
+                _ => {}
+            }
+
+            // If it's already hoisted, it means that it is already processed by child
+            // scope.
+            if v.hoisted.get() {
+                return false;
+            }
+        }
+
+        {
+            let mut cur = Some(self);
+
+            while let Some(scope) = cur {
+                let found = scope.find_binding_from_current(id).is_some();
+
+                if found {
+                    log::trace!("found");
+                    break;
+                }
+                log::debug!("({}): {}: kind = {:?}", scope.depth(), id.0, scope.kind);
+
+                match scope.kind {
+                    ScopeKind::Fn { .. } => {
+                        log::debug!("{}: variable access from a nested function detected", id.0);
+                        return true;
+                    }
+                    ScopeKind::Loop | ScopeKind::Cond => {
+                        return true;
+                    }
+                    _ => {}
+                }
+                cur = scope.parent;
+            }
+        }
+
+        false
+    }
+
+    pub fn add_read(&mut self, id: &Id) {
+        if self.read_prevents_inlining(id) {
+            log::debug!("prevent inlining because of read: {}", id.0);
+
+            self.prevent_inline(id)
+        }
+
+        if id.0 == js_word!("arguments") {
+            self.prevent_inline_of_params();
+        }
+
+        if let Some(var_info) = self.find_binding(id) {
+            var_info.read_cnt.set(var_info.read_cnt.get() + 1);
+            if var_info.hoisted.get() {
+                var_info.inline_prevented.set(true);
+            }
+        } else {
+            log::trace!("({}): Unresolved usage.: {:?}", self.depth(), id);
+            self.unresolved_usages.insert(id.clone());
+        }
+
+        let (scope, is_self) = self.scope_for(id);
+        if !is_self {
+            if let Some(var_info) = scope.find_binding_from_current(id) {
+                var_info.read_from_nested_scope.set(true);
+            }
+        }
+    }
+
+    fn write_prevents_inline(&self, id: &Id) -> bool {
+        log::trace!("write_prevents_inline({})", id.0);
+
+        {
+            let mut cur = Some(self);
+
+            while let Some(scope) = cur {
+                let found = scope.find_binding_from_current(id).is_some();
+
+                if found {
+                    break;
+                }
+                log::debug!("({}): {}: kind = {:?}", scope.depth(), id.0, scope.kind);
+
+                match scope.kind {
+                    ScopeKind::Fn { .. } => {
+                        log::debug!("{}: variable access from a nested function detected", id.0);
+                        return true;
+                    }
+                    ScopeKind::Loop | ScopeKind::Cond => {
+                        return true;
+                    }
+                    _ => {}
+                }
+                cur = scope.parent;
+            }
+        }
+
+        false
+    }
+
+    pub fn add_write(&mut self, id: &Id, force_no_inline: bool) {
+        if self.write_prevents_inline(id) {
+            log::debug!("prevent inlining because of write: {}", id.0);
+
+            self.prevent_inline(id)
+        }
+
+        if id.0 == js_word!("arguments") {
+            self.prevent_inline_of_params();
+        }
+
+        let (scope, is_self) = self.scope_for(id);
+
+        if let Some(var_info) = scope.find_binding_from_current(id) {
+            var_info.is_undefined.set(false);
+
+            if !is_self || force_no_inline {
+                self.prevent_inline(id)
+            }
+        } else if self.has_constant(id) {
+            // noop
+        } else {
+            log::trace!(
+                "({}): Unresolved. (scope = ({})): {:?}",
+                self.depth(),
+                scope.depth(),
+                id
+            );
+            self.bindings.insert(
+                id.clone(),
+                VarInfo {
+                    kind: VarType::Var(VarDeclKind::Var),
+                    alias_of: None,
+                    read_from_nested_scope: Cell::new(false),
+                    read_cnt: Cell::new(0),
+                    inline_prevented: Cell::new(force_no_inline),
+                    value: RefCell::new(None),
+                    is_undefined: Cell::new(false),
+                    this_sensitive: Cell::new(false),
+                    hoisted: Cell::new(false),
+                },
+            );
+        }
+    }
+
+    pub fn find_binding(&self, id: &Id) -> Option<&VarInfo> {
+        if let Some(e) = self.find_binding_from_current(id) {
+            return Some(e);
+        }
+
+        self.parent.and_then(|parent| parent.find_binding(id))
+    }
+
+    /// Searches only for current scope.
+    fn idx_val(&self, id: &Id) -> Option<(usize, &VarInfo)> {
+        self.bindings.iter().enumerate().find_map(
+            |(idx, (k, v))| {
+                if k == id {
+                    Some((idx, v))
+                } else {
+                    None
+                }
+            },
+        )
+    }
+
+    pub fn find_binding_from_current(&self, id: &Id) -> Option<&VarInfo> {
+        let (_, v) = self.idx_val(id)?;
+
+        Some(v)
+    }
+
+    fn has_constant(&self, id: &Id) -> bool {
+        if let Some(..) = self.constants.get(id) {
+            return true;
+        }
+
+        self.parent
+            .map(|parent| parent.has_constant(id))
+            .unwrap_or(false)
+    }
+
+    pub fn find_constant(&self, id: &Id) -> Option<&Expr> {
+        if let Some(Some(e)) = self.constants.get(id) {
+            return Some(e);
+        }
+
+        self.parent.and_then(|parent| parent.find_constant(id))
+    }
+
+    pub fn mark_this_sensitive(&self, callee: &Expr) {
+        match callee {
+            Expr::Ident(ref i) => {
+                if let Some(v) = self.find_binding(&i.to_id()) {
+                    v.this_sensitive.set(true);
+                }
+            }
+
+            _ => {}
+        }
+    }
+
+    pub fn store_inline_barrier(&self, phase: Phase) {
+        log::trace!("store_inline_barrier({:?})", phase);
+
+        match phase {
+            Phase::Analysis => {
+                let idx = self.bindings.len();
+                self.inline_barriers.borrow_mut().push_back(idx);
+            }
+            Phase::Inlining => {
+                //if let Some(idx) =
+                // self.inline_barriers.borrow_mut().pop_front() {
+                //    for i in 0..idx {
+                //        if let Some((id, _)) = self.bindings.get_index(i) {
+                //            self.prevent_inline(id);
+                //        }
+                //    }
+                //}
+            }
+        }
+
+        match self.parent {
+            None => {}
+            Some(p) => p.store_inline_barrier(phase),
+        }
+    }
+
+    fn prevent_inline_of_params(&self) {
+        for (_, v) in self.bindings.iter() {
+            let v: &VarInfo = v;
+
+            if v.is_param() {
+                v.inline_prevented.set(true);
+            }
+        }
+
+        if let ScopeKind::Fn { .. } = self.kind {
+            return;
+        }
+
+        match self.parent {
+            Some(p) => p.prevent_inline_of_params(),
+            None => {}
+        }
+    }
+
+    pub fn prevent_inline(&self, id: &Id) {
+        log::debug!("({}) Prevent inlining: {:?}", self.depth(), id);
+
+        if let Some(v) = self.find_binding_from_current(id) {
+            v.inline_prevented.set(true);
+        }
+
+        for (_, v) in self.bindings.iter() {
+            match v.value.borrow().as_ref() {
+                Some(&Expr::Ident(ref i)) => {
+                    if i.sym == id.0 && i.span.ctxt() == id.1 {
+                        v.inline_prevented.set(true);
+                    }
+                }
+
+                _ => {}
+            }
+        }
+
+        match self.parent {
+            None => {}
+            Some(p) => p.prevent_inline(id),
+        }
+    }
+
+    pub fn is_inline_prevented(&self, e: &Expr) -> bool {
+        match *e {
+            Expr::Ident(ref ri) => {
+                if let Some(v) = self.find_binding_from_current(&ri.to_id()) {
+                    return v.inline_prevented.get();
+                }
+            }
+            Expr::Member(MemberExpr {
+                obj: ExprOrSuper::Expr(box Expr::Ident(ref ri)),
+                ..
+            }) => {
+                if let Some(v) = self.find_binding_from_current(&ri.to_id()) {
+                    return v.inline_prevented.get();
+                }
+            }
+            Expr::Update(..) => return true,
+
+            // TODO: Remove this
+            Expr::Paren(..) | Expr::Call(..) | Expr::New(..) => return true,
+
+            _ => {}
+        }
+
+        match self.parent {
+            None => false,
+            Some(p) => p.is_inline_prevented(e),
+        }
+    }
+
+    pub fn has_same_this(&self, id: &Id, init: Option<&Expr>) -> bool {
+        if let Some(v) = self.find_binding(id) {
+            if v.this_sensitive.get() {
+                match init {
+                    Some(&Expr::Member(..)) => return false,
+                    _ => {}
+                }
+            }
+        }
+
+        true
+    }
+}
+
+#[derive(Debug)]
+pub(super) struct VarInfo {
+    pub kind: VarType,
+
+    alias_of: Option<VarType>,
+
+    read_from_nested_scope: Cell<bool>,
+    read_cnt: Cell<usize>,
+
+    inline_prevented: Cell<bool>,
+    this_sensitive: Cell<bool>,
+
+    pub value: RefCell<Option<Expr>>,
+    pub is_undefined: Cell<bool>,
+
+    hoisted: Cell<bool>,
+}
+
+impl VarInfo {
+    pub fn is_param(&self) -> bool {
+        self.kind == VarType::Param
+    }
+
+    pub fn is_inline_prevented(&self) -> bool {
+        if self.inline_prevented.get() {
+            return true;
+        }
+
+        if self.this_sensitive.get() {
+            match *self.value.borrow() {
+                Some(Expr::Member(..)) => return true,
+                _ => {}
+            }
+        }
+
+        false
+    }
+}

ecmascript/transforms/src/optimization/simplify/mod.rs

@@ -0,0 +1,26 @@
+//! Ported from closure compiler.
+pub use self::{branch::dead_branch_remover, expr::expr_simplifier};
+use crate::pass::RepeatedJsPass;
+use swc_common::{chain, pass::Repeat};
+
+mod branch;
+pub mod dce;
+mod expr;
+pub mod inlining;
+
+#[derive(Debug, Default)]
+pub struct Config<'a> {
+    pub dce: dce::Config<'a>,
+    pub inlining: inlining::Config,
+}
+
+/// Performs simplify-expr, inlining, remove-dead-branch and dce until nothing
+/// changes.
+pub fn simplifier<'a>(c: Config<'a>) -> impl RepeatedJsPass + 'a {
+    Repeat::new(chain!(
+        expr_simplifier(),
+        inlining::inlining(c.inlining),
+        dead_branch_remover(),
+        dce::dce(c.dce)
+    ))
+}

ecmascript/transforms/src/pass.rs

@@ -1,5 +1,8 @@
 use std::marker::PhantomData;
-use swc_common::{Fold, FoldWith};
+use swc_common::{
+    pass::{Repeated, RepeatedPass},
+    Fold, FoldWith,
+};
 use swc_ecma_ast::*;
 
 pub fn noop() -> impl Pass {
@@ -210,3 +213,10 @@ where
         node.fold_children(self)
     }
 }
+
+pub trait RepeatedJsPass:
+    Repeated + RepeatedPass<Program> + RepeatedPass<Module> + RepeatedPass<Script> + Pass
+{
+}
+
+impl<P> RepeatedJsPass for P where P: Repeated + Pass {}

ecmascript/transforms/src/resolver.rs

@@ -360,6 +360,28 @@ impl<'a> Fold<Ident> for Resolver<'a> {
                     if cfg!(debug_assertions) && LOG {
                         eprintln!("\t -> Unresolved");
                     }
+
+                    let mark = {
+                        let mut mark = self.mark;
+                        let mut cur = Some(&self.current);
+                        while let Some(scope) = cur {
+                            cur = scope.parent;
+
+                            if cur.is_none() {
+                                break;
+                            }
+                            mark = mark.parent();
+                        }
+
+                        mark
+                    };
+
+                    let span = span.apply_mark(mark);
+
+                    if cfg!(debug_assertions) && LOG {
+                        eprintln!("\t -> {:?}", span.ctxt());
+                    }
+
                     // Support hoisting
                     self.fold_binding_ident(Ident { sym, span, ..i })
                 }

ecmascript/transforms/src/resolver/tests.rs

@@ -1044,3 +1044,12 @@ test!(
     Object1.defineProperty();
 }"
 );
+
+identical!(
+    hoisting,
+    "function foo() {
+        return XXX
+    }
+    var XXX = 1;
+    "
+);

ecmascript/transforms/tests/common/mod.rs

@@ -200,6 +200,7 @@ where
         let expected =
             tester.apply_transform(::testing::DropSpan, "output.js", syntax, expected)?;
 
+        println!(">>>>> Orig <<<<<\n{}", input);
         println!("----- Actual -----");
 
         let tr = make_tr("actual", tr, tester);
@@ -236,7 +237,6 @@ where
             return Err(());
         }
 
-        println!(">>>>> Orig <<<<<\n{}", input);
         println!(">>>>> Code <<<<<\n{}", actual_src);
         if actual_src != expected_src {
             panic!(

ecmascript/transforms/tests/fixer_test262.rs

@@ -111,7 +111,7 @@ struct MyHandlers;
 
 impl swc_ecma_codegen::Handlers for MyHandlers {}
 
-fn error_tests(tests: &mut Vec<TestDescAndFn>) -> Result<(), io::Error> {
+fn identity_tests(tests: &mut Vec<TestDescAndFn>) -> Result<(), io::Error> {
     let dir = Path::new(env!("CARGO_MANIFEST_DIR"))
         .parent()
         .unwrap()
@@ -269,7 +269,7 @@ fn error_tests(tests: &mut Vec<TestDescAndFn>) -> Result<(), io::Error> {
 fn identity() {
     let args: Vec<_> = env::args().collect();
     let mut tests = Vec::new();
-    error_tests(&mut tests).expect("failed to load testss");
+    identity_tests(&mut tests).expect("failed to load testss");
     test_main(&args, tests, Some(Options::new()));
 }
 

ecmascript/transforms/tests/modules_common_js.rs

@@ -113,7 +113,7 @@ test!(
         decorators(Default::default()),
         class_properties(),
         export(),
-        simplifier(),
+        simplifier(Default::default()),
         compat::es2018(),
         compat::es2017(),
         compat::es2016(),

ecmascript/transforms/tests/optimization_simplify.rs

@@ -0,0 +1,448 @@
+//! Copied from PeepholeIntegrationTest from the google closure compiler.
+
+#![feature(box_syntax)]
+#![feature(test)]
+#![feature(box_patterns)]
+#![feature(specialization)]
+
+use swc_common::chain;
+use swc_ecma_transforms::{optimization::simplifier, resolver};
+
+#[macro_use]
+mod common;
+
+fn test(src: &str, expected: &str) {
+    test_transform!(
+        ::swc_ecma_parser::Syntax::default(),
+        |_| chain!(resolver(), simplifier(Default::default())),
+        src,
+        expected,
+        true
+    )
+}
+
+fn test_same(src: &str) {
+    test(src, src)
+}
+
+macro_rules! to {
+    ($name:ident, $src:expr, $expected:expr) => {
+        test!(
+            Default::default(),
+            |_| chain!(resolver(), simplifier(Default::default())),
+            $name,
+            $src,
+            $expected
+        );
+    };
+}
+
+macro_rules! optimized_out {
+    ($name:ident, $src:expr) => {
+        to!($name, $src, "");
+    };
+}
+
+optimized_out!(
+    single_pass,
+    "
+const a = 1;
+
+if (a) {
+    const b = 2;
+}
+"
+);
+
+optimized_out!(issue_607, "let a");
+
+to!(
+    multi_run,
+    "
+let b = 2;
+
+let a = 1;
+if (b) { // Removed by first run of remove_dead_branch
+    a = 2; // It becomes `flat assignment` to a on second run of inlining
+}
+
+let c;
+if (a) { // Removed by second run of remove_dead_branch
+    c = 3; // It becomes `flat assignment` to c on third run of inlining.
+}
+console.log(c); // Prevent optimizing out.
+",
+    "console.log(3)"
+);
+
+#[test]
+#[ignore] // TODO
+fn test_fold_one_child_blocks_integration() {
+    test(
+        "function f(){switch(foo()){default:{break}}}",
+        "function f(){foo()}",
+    );
+
+    test(
+        "function f(){switch(x){default:{break}}} use(f);",
+        "function f(){} use(f);",
+    );
+
+    test(
+        "function f(){switch(x){default:x;case 1:return 2}} use(f);",
+        "function f(){switch(x){default:case 1:return 2}} use(f);",
+    );
+
+    // ensure that block folding does not break hook ifs
+    test(
+        "if(x){if(true){foo();foo()}else{bar();bar()}}",
+        "if(x){foo();foo()}",
+    );
+
+    test(
+        "if(x){if(false){foo();foo()}else{bar();bar()}}",
+        "if(x){bar();bar()}",
+    );
+
+    // Cases where the then clause has no side effects.
+    test("if(x()){}", "x()");
+
+    test("if(x()){} else {x()}", "x()||x()");
+    test("if(x){}", ""); // Even the condition has no side effect.
+    test(
+        "if(a()){A()} else if (b()) {} else {C()}",
+        "a()?A():b()||C()",
+    );
+
+    test(
+        "if(a()){} else if (b()) {} else {C()}",
+        "a() || (b() || C())",
+    );
+    test(
+        "if(a()){A()} else if (b()) {} else if (c()) {} else{D()}",
+        "a() ? A() : b() || (c() || D())",
+    );
+    test(
+        "if(a()){} else if (b()) {} else if (c()) {} else{D()}",
+        "a() || (b() || (c() || D()))",
+    );
+    test(
+        "if(a()){A()} else if (b()) {} else if (c()) {} else{}",
+        "a()?A():b()||c()",
+    );
+
+    // Verify that non-global scope works.
+    test("function foo(){if(x()){}}", "function foo(){x()}");
+}
+
+#[test]
+#[ignore] // swc optimizes out everything
+fn test_fold_one_child_blocks_string_compare() {
+    test(
+        "if (x) {if (y) { var x; } } else{ var z; }",
+        "if (x) { if (y) var x } else var z",
+    );
+}
+
+#[test]
+fn test_necessary_dangling_else() {
+    test(
+        "if (x) if (y){ y(); z() } else; else x()",
+        "if (x) { if(y) { y(); z() } } else x()",
+    );
+}
+
+#[test]
+#[ignore] // TODO
+fn test_fold_returns_integration() {
+    // if-then-else duplicate statement removal handles this case:
+    test("function f(){if(x)return;else return}", "function f(){}");
+}
+
+#[test]
+fn test_bug1059649() {
+    // ensure that folding blocks with a single var node doesn't explode
+    test(
+        "if(x){var y=3;}var z=5; use(y, z)",
+        "if(x)var y=3; use(y, 5)",
+    );
+
+    test(
+        "for(var i=0;i<10;i++){var y=3;}var z=5; use(y, z)",
+        "for(var i=0;i<10;i++)var y=3; use(y, 5)",
+    );
+    test(
+        "for(var i in x){var y=3;}var z=5; use(y, z)",
+        "for(var i in x)var y=3; use(y, 5)",
+    );
+    test(
+        "do{var y=3;}while(x);var z=5; use(y, z)",
+        "do var y=3;while(x); use(y, 5)",
+    );
+}
+
+#[test]
+#[ignore] // TODO
+fn test_hook_if_integration() {
+    test(
+        "if (false){ x = 1; } else if (cond) { x = 2; } else { x = 3; }",
+        "x=cond?2:3",
+    );
+
+    test("x?void 0:y()", "x||y()");
+    test("!x?void 0:y()", "x&&y()");
+    test("x?y():void 0", "x&&y()");
+}
+
+#[test]
+#[ignore] // normalize
+fn test_remove_duplicate_statements_integration() {
+    test(
+        concat!(
+            "function z() {if (a) { return true }",
+            "else if (b) { return true }",
+            "else { return true }}",
+        ),
+        "function z() {return true;}",
+    );
+
+    test(
+        concat!(
+            "function z() {if (a()) { return true }",
+            "else if (b()) { return true }",
+            "else { return true }}",
+        ),
+        "function z() {a()||b();return true;}",
+    );
+}
+
+#[test]
+#[ignore] // TODO
+fn test_fold_logical_op_integration() {
+    test("if(x && true) z()", "x&&z()");
+    test("if(x && false) z()", "");
+    test("if(x || 3) z()", "z()");
+    test("if(x || false) z()", "x&&z()");
+    test("if(x==y && false) z()", "");
+    test("if(y() || x || 3) z()", "y();z()");
+}
+
+#[test]
+#[ignore] // TODO: This is a bug, but does anyone write code like this?
+fn test_fold_bitwise_op_string_compare_integration() {
+    test("for (;-1 | 0;) {}", "for (;;);");
+}
+
+#[test]
+fn test_var_lifting_integration() {
+    test("if(true);else var a;", "");
+    test("if(false) foo();else var a;", "");
+    test("if(true)var a;else;", "");
+    test("if(false)var a;else;", "");
+    test("if(false)var a,b;", "");
+    test("if(false){var a;var a;}", "");
+    test("if(false)var a=function(){var b};", "");
+    test("if(a)if(false)var a;else var b;", "");
+}
+
+#[test]
+fn test_bug1438784() {
+    test_same("for(var i=0;i<10;i++)if(x)x.y;");
+}
+
+#[test]
+fn test_fold_useless_for_integration() {
+    test("for(;!true;) { foo() }", "");
+    test("for(;void 0;) { foo() }", "");
+    test("for(;undefined;) { foo() }", "");
+    test("for(;1;) foo()", "for(;;) foo()");
+    test("for(;!void 0;) foo()", "for(;;) foo()");
+
+    // Make sure proper empty nodes are inserted.
+    //    test("if(foo())for(;false;){foo()}else bar()", "foo()||bar()");
+    test(
+        "if(foo())for(;false;){foo()}else bar()",
+        "if (foo()); else bar();",
+    );
+}
+
+#[test]
+fn test_fold_useless_do_integration() {
+    test("do { foo() } while(!true);", "foo()");
+    test("do { foo() } while(void 0);", "foo()");
+    test("do { foo() } while(undefined);", "foo()");
+    test("do { foo() } while(!void 0);", "for(;;)foo();");
+
+    // Make sure proper empty nodes are inserted.
+    //    test(
+    //        "if(foo())do {foo()} while(false) else bar()",
+    //        "foo()?foo():bar()",
+    //    );
+
+    test(
+        "if(foo())do {foo()} while(false) else bar()",
+        "if (foo()) foo(); else bar();",
+    );
+}
+
+#[test]
+#[ignore] // TODO
+fn test_minimize_expr() {
+    test("!!true", "");
+
+    test("!!x()", "x()");
+    test("!(!x()&&!y())", "x()||y()");
+    test("x()||!!y()", "x()||y()");
+
+    /* This is similar to the !!true case */
+    test("!!x()&&y()", "x()&&y()");
+}
+
+#[test]
+fn test_bug_issue3() {
+    test_same(concat!(
+        "function foo() {",
+        "  if(sections.length != 1) children[i] = 0;",
+        "  else var selectedid = children[i]",
+        "}",
+    ));
+}
+
+#[test]
+fn test_bug_issue43() {
+    test_same("function foo() {\n  if (a) var b = bar(); else a.b = 1; \n} use(foo);");
+}
+
+#[test]
+fn test_fold_negative_bug() {
+    test("for (;-3;){};", "for (;;);");
+}
+
+#[test]
+#[ignore] // normalize
+fn test_no_normalize_labeled_expr() {
+    test_same("var x; foo:{x = 3;}");
+    test_same("var x; foo:x = 3;");
+}
+
+#[test]
+fn test_short_circuit1() {
+    test("1 && a()", "a()");
+}
+
+#[test]
+fn test_short_circuit2() {
+    test("1 && a() && 2", "a()");
+}
+
+#[test]
+fn test_short_circuit3() {
+    test("a() && 1 && 2", "a()");
+}
+
+#[test]
+#[ignore]
+fn test_short_circuit4() {
+    test("a() && (1 && b())", "a() && b()");
+    test("a() && 1 && b()", "a() && b()");
+    test("(a() && 1) && b()", "a() && b()");
+}
+
+#[test]
+#[ignore] // TODO
+fn test_minimize_expr_condition() {
+    test("(x || true) && y()", "y()");
+    test("(x || false) && y()", "x&&y()");
+    test("(x && true) && y()", "x && y()");
+    test("(x && false) && y()", "");
+    test("a = x || false ? b : c", "a=x?b:c");
+    test("do {x()} while((x && false) && y())", "x()");
+}
+
+// A few miscellaneous cases where one of the peephole passes increases the
+// size, but it does it in such a way that a later pass can decrease it.
+// Test to make sure the overall change is a decrease, not an increase.
+#[test]
+#[ignore] // TODO
+fn test_misc() {
+    test("use(x = [foo()] && x)", "use(x = (foo(),x))");
+    test("x = foo() && false || bar()", "x = (foo(), bar())");
+    test("if(foo() && false) z()", "foo()");
+}
+
+#[test]
+#[ignore] // swc strips out whole of this
+fn test_comma_spliting_constant_condition() {
+    test("(b=0,b=1);if(b)x=b;", "b=0;b=1;x=b;");
+    test("(b=0,b=1);if(b)x=b;", "b=0;b=1;x=b;");
+}
+
+#[test]
+#[ignore]
+fn test_avoid_comma_splitting() {
+    test("x(),y(),z()", "x();y();z()");
+}
+
+#[test]
+fn test_object_literal() {
+    test("({})", "");
+    test("({a:1})", "");
+    test("({a:foo()})", "foo()");
+    test("({'a':foo()})", "foo()");
+}
+
+#[test]
+fn test_array_literal() {
+    test("([])", "");
+    test("([1])", "");
+    test("([a])", "");
+    test("([foo()])", "foo()");
+}
+
+#[test]
+#[ignore] // TODO
+fn test_fold_ifs1() {
+    test(
+        "function f() {if (x) return 1; else if (y) return 1;}",
+        "function f() {if (x||y) return 1;}",
+    );
+    test(
+        "function f() {if (x) return 1; else {if (y) return 1; else foo();}}",
+        "function f() {if (x||y) return 1; foo();}",
+    );
+}
+
+#[test]
+#[ignore] // TODO
+fn test_fold_ifs2() {
+    test(
+        "function f() {if (x) { a(); } else if (y) { a() }}",
+        "function f() {x?a():y&&a();}",
+    );
+}
+
+#[test]
+#[ignore] // TODO
+fn test_fold_hook2() {
+    test(
+        "function f(a) {if (!a) return a; else return a;}",
+        "function f(a) {return a}",
+    );
+}
+
+#[test]
+#[ignore] // TODO
+fn test_template_strings_known_methods() {
+    test("x = `abcdef`.indexOf('b')", "x = 1");
+    test("x = [`a`, `b`, `c`].join(``)", "x='abc'");
+    test("x = `abcdef`.substr(0,2)", "x = 'ab'");
+    test("x = `abcdef`.substring(0,2)", "x = 'ab'");
+    test("x = `abcdef`.slice(0,2)", "x = 'ab'");
+    test("x = `abcdef`.charAt(0)", "x = 'a'");
+    test("x = `abcdef`.charCodeAt(0)", "x = 97");
+    test("x = `abc`.toUpperCase()", "x = 'ABC'");
+    test("x = `ABC`.toLowerCase()", "x = 'abc'");
+    //test("x = `\t\n\uFEFF\t asd foo bar \r\n`.trim()", "x = 'asd foo bar'");
+    test("x = parseInt(`123`)", "x = 123");
+    test("x = parseFloat(`1.23`)", "x = 1.23");
+}

ecmascript/transforms/tests/optimization_simplify_dce.rs

@@ -0,0 +1,106 @@
+#![feature(box_syntax)]
+#![feature(test)]
+#![feature(box_patterns)]
+#![feature(specialization)]
+
+use swc_common::chain;
+use swc_ecma_transforms::{optimization::simplify::dce::dce, resolver};
+
+#[macro_use]
+mod common;
+
+macro_rules! to {
+    ($name:ident, $src:expr, $expected:expr) => {
+        test!(
+            Default::default(),
+            |_| chain!(resolver(), dce(Default::default())),
+            $name,
+            $src,
+            $expected
+        );
+    };
+}
+
+macro_rules! optimized_out {
+    ($name:ident, $src:expr) => {
+        to!($name, $src, "");
+    };
+}
+
+macro_rules! noop {
+    ($name:ident, $src:expr) => {
+        to!($name, $src, $src);
+    };
+}
+
+optimized_out!(
+    single_pass,
+    "
+const a = 1;
+
+if (a) {
+    const b = 2;
+}
+"
+);
+
+optimized_out!(issue_607, "let a");
+
+noop!(
+    noop_1,
+    "
+let b = 2;
+
+let a = 1;
+if (b) {
+    a = 2;
+}
+
+let c;
+if (a) {
+    c = 3;
+}
+console.log(c);
+"
+);
+
+noop!(
+    noop_2,
+    "
+switch (1){
+    case 1: 
+        a = '1';
+}
+
+console.log(a);
+"
+);
+
+noop!(
+    noop_3,
+    "
+try {
+    console.log(foo())
+} catch (e) {
+    console.error(e);
+}"
+);
+
+to!(
+    custom_loop_2,
+    "let b = 2;
+
+let a = 1;
+a = 2;
+
+let c;
+if (2) c = 3
+console.log(c)",
+    "let c;
+if (2) c = 3;
+console.log(c);"
+);
+
+optimized_out!(simple_const, "{const x = 1}");
+
+noop!(assign_op, "x *= 2; use(x)");

ecmascript/utils/src/lib.rs

@@ -477,6 +477,25 @@ pub trait ExprExt {
                 v
             }
 
+            Expr::Bin(BinExpr {
+                ref left,
+                op: op!("||"),
+                ref right,
+                ..
+            }) => {
+                let (lp, lv) = left.as_bool();
+                if let Known(true) = lv {
+                    return (lp, lv);
+                }
+
+                let (rp, rv) = right.as_bool();
+                if let Known(true) = rv {
+                    return (lp + rp, rv);
+                }
+
+                Unknown
+            }
+
             Expr::Fn(..) | Expr::Class(..) | Expr::New(..) | Expr::Array(..) | Expr::Object(..) => {
                 Known(true)
             }
@@ -1353,7 +1372,7 @@ pub fn undefined(span: Span) -> Box<Expr> {
     })
 }
 
-/// inject `stmt` after directives
+/// inject `branch` after directives
 #[inline(never)]
 pub fn prepend<T: StmtLike>(stmts: &mut Vec<T>, stmt: T) {
     let idx = stmts

scripts/rustdoc.sh

@@ -1,40 +0,0 @@
-#!/bin/bash
-set -eu
-
-crate_name() {
-    POSITIONAL=()
-    while [[ $# -gt 0 ]]
-    do
-    key="$1"
-
-    case $key in
-        --crate-name)
-        CRATE_NAME="$2"
-        shift # past argument
-        shift # past value
-        ;;
-        *)    # unknown option
-        POSITIONAL+=("$1") # save it in an array for later
-        shift # past argument
-        ;;
-    esac
-    done
-    set -- "${POSITIONAL[@]}" # restore positional parameters
-
-    echo "$CRATE_NAME"
-}
-
-cr=$(crate_name "$@")
-if [[ $cr == swc* ]]; then
-    # We use this instead of --document-private-items to
-    # make output simillar to usage from outside.
-    #
-    # e.g. this inlines self::stmt::*, and when we're using ecmascript::ast, 
-    #   we can't use ecmascript::ast::stmt because it's private.  
-#     rustdoc --passes strip-hidden,unindent-comments,\
-# collapse-docs,strip-priv-imports,propagate-doc-cfg $@  
-    rustdoc --document-private-items $@
-else
-    rustdoc $@
-fi
-

src/config.rs

@@ -206,7 +206,7 @@ impl Options {
                 export(),
                 syntax.export_default_from() || syntax.export_namespace_from()
             ),
-            Optional::new(simplifier(), enable_optimizer),
+            Optional::new(simplifier(Default::default()), enable_optimizer),
             json_parse_pass
         );
 

testing/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "testing"
-version = "0.5.0"
+version = "0.5.1"
 authors = ["강동윤 <kdy1997.dev@gmail.com>"]
 license = "Apache-2.0/MIT"
 repository = "https://github.com/swc-project/swc.git"
@@ -14,3 +14,6 @@ once_cell = "1"
 regex = "1"
 relative-path = "1"
 difference = "2"
+log = "0.4"
+env_logger = "0.7.1"
+ansi_term = "0.12.1"

testing/src/lib.rs

@@ -8,6 +8,7 @@ use difference::Changeset;
 use once_cell::sync::Lazy;
 use regex::Regex;
 use std::{
+    fmt,
     fmt::Debug,
     fs::{create_dir_all, File},
     io::Write,
@@ -27,11 +28,48 @@ mod output;
 mod paths;
 mod string_errors;
 
+/// Configures logger
+pub fn init() {
+    use ansi_term::Color;
+
+    struct Padded<T> {
+        value: T,
+        width: usize,
+    }
+
+    impl<T: fmt::Display> fmt::Display for Padded<T> {
+        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+            write!(f, "{: <width$}", self.value, width = self.width)
+        }
+    }
+
+    fn colored_level<'a>(level: log::Level) -> String {
+        match level {
+            log::Level::Trace => Color::Cyan.paint("TRACE").to_string(),
+            log::Level::Debug => Color::Blue.paint("TRACE").to_string(),
+            log::Level::Info => Color::Green.paint("INFO ").to_string(),
+            log::Level::Warn => Color::Yellow.paint("WARN ").to_string(),
+            log::Level::Error => Color::Red.paint("ERROR").to_string(),
+        }
+    }
+
+    let _ = env_logger::Builder::from_default_env()
+        .is_test(true)
+        .format(|f, record| {
+            let level = colored_level(record.level());
+
+            writeln!(f, " {} > {}", level, record.args(),)
+        })
+        .try_init();
+}
+
 /// Run test and print errors.
 pub fn run_test<F, Ret>(treat_err_as_bug: bool, op: F) -> Result<Ret, StdErr>
 where
     F: FnOnce(Arc<SourceMap>, &Handler) -> Result<Ret, ()>,
 {
+    init();
+
     let cm = Arc::new(SourceMap::new(FilePathMapping::empty()));
     let (handler, errors) = self::string_errors::new_handler(cm.clone(), treat_err_as_bug);
     let result = swc_common::GLOBALS.set(&swc_common::Globals::new(), || op(cm, &handler));
@@ -47,6 +85,8 @@ pub fn run_test2<F, Ret>(treat_err_as_bug: bool, op: F) -> Result<Ret, StdErr>
 where
     F: FnOnce(Arc<SourceMap>, Handler) -> Result<Ret, ()>,
 {
+    init();
+
     let cm = Arc::new(SourceMap::new(FilePathMapping::empty()));
     let (handler, errors) = self::string_errors::new_handler(cm.clone(), treat_err_as_bug);
     let result = swc_common::GLOBALS.set(&swc_common::Globals::new(), || op(cm, handler));
@@ -64,6 +104,8 @@ pub struct Tester {
 
 impl Tester {
     pub fn new() -> Self {
+        init();
+
         Tester {
             cm: Arc::new(SourceMap::new(FilePathMapping::empty())),
             globals: swc_common::Globals::new(),

tests/projects/issue-409-1/input.js

@@ -1 +1,2 @@
 let a = { b: 'c' };
+use(a)