perf(es/minifier): Make more passes parallel (#4821)

crates/swc_ecma_minifier/src/compress/optimize/if_return.rs

@@ -1,6 +1,6 @@
 use swc_common::{util::take::Take, Spanned, DUMMY_SP};
 use swc_ecma_ast::*;
-use swc_ecma_utils::{prepend_stmt, undefined, StmtExt, StmtLike};
+use swc_ecma_utils::{undefined, StmtExt, StmtLike};
 use swc_ecma_visit::{noop_visit_type, Visit, VisitWith};
 
 use super::Optimizer;
@@ -41,58 +41,6 @@ where
         }
     }
 
-    pub(super) fn merge_else_if(&mut self, s: &mut IfStmt) {
-        if let Some(Stmt::If(IfStmt {
-            span: span_of_alt,
-            test: test_of_alt,
-            cons: cons_of_alt,
-            alt: Some(alt_of_alt),
-            ..
-        })) = s.alt.as_deref_mut()
-        {
-            match &**cons_of_alt {
-                Stmt::Return(..) | Stmt::Continue(ContinueStmt { label: None, .. }) => {}
-                _ => return,
-            }
-
-            match &mut **alt_of_alt {
-                Stmt::Block(..) => {}
-                Stmt::Expr(..) => {
-                    *alt_of_alt = Box::new(Stmt::Block(BlockStmt {
-                        span: DUMMY_SP,
-                        stmts: vec![*alt_of_alt.take()],
-                    }));
-                }
-                _ => {
-                    return;
-                }
-            }
-
-            self.changed = true;
-            report_change!("if_return: Merging `else if` into `else`");
-
-            match &mut **alt_of_alt {
-                Stmt::Block(alt_of_alt) => {
-                    prepend_stmt(
-                        &mut alt_of_alt.stmts,
-                        Stmt::If(IfStmt {
-                            span: *span_of_alt,
-                            test: test_of_alt.take(),
-                            cons: cons_of_alt.take(),
-                            alt: None,
-                        }),
-                    );
-                }
-
-                _ => {
-                    unreachable!()
-                }
-            }
-
-            s.alt = Some(alt_of_alt.take());
-        }
-    }
-
     pub(super) fn merge_if_returns(
         &mut self,
         stmts: &mut Vec<Stmt>,

crates/swc_ecma_minifier/src/compress/optimize/mod.rs

@@ -2039,8 +2039,6 @@ where
         self.negate_if_stmt(n);
 
         self.merge_nested_if(n);
-
-        self.merge_else_if(n);
     }
 
     #[cfg_attr(feature = "debug", tracing::instrument(skip_all))]

crates/swc_ecma_minifier/src/compress/pure/if_return.rs

@@ -1,5 +1,6 @@
 use swc_common::{util::take::Take, DUMMY_SP};
 use swc_ecma_ast::*;
+use swc_ecma_utils::prepend_stmt;
 
 use super::Pure;
 use crate::compress::util::{is_fine_for_if_cons, negate};
@@ -125,4 +126,56 @@ impl Pure<'_> {
 
         *stmts = new;
     }
+
+    pub(super) fn merge_else_if(&mut self, s: &mut IfStmt) {
+        if let Some(Stmt::If(IfStmt {
+            span: span_of_alt,
+            test: test_of_alt,
+            cons: cons_of_alt,
+            alt: Some(alt_of_alt),
+            ..
+        })) = s.alt.as_deref_mut()
+        {
+            match &**cons_of_alt {
+                Stmt::Return(..) | Stmt::Continue(ContinueStmt { label: None, .. }) => {}
+                _ => return,
+            }
+
+            match &mut **alt_of_alt {
+                Stmt::Block(..) => {}
+                Stmt::Expr(..) => {
+                    *alt_of_alt = Box::new(Stmt::Block(BlockStmt {
+                        span: DUMMY_SP,
+                        stmts: vec![*alt_of_alt.take()],
+                    }));
+                }
+                _ => {
+                    return;
+                }
+            }
+
+            self.changed = true;
+            report_change!("if_return: Merging `else if` into `else`");
+
+            match &mut **alt_of_alt {
+                Stmt::Block(alt_of_alt) => {
+                    prepend_stmt(
+                        &mut alt_of_alt.stmts,
+                        Stmt::If(IfStmt {
+                            span: *span_of_alt,
+                            test: test_of_alt.take(),
+                            cons: cons_of_alt.take(),
+                            alt: None,
+                        }),
+                    );
+                }
+
+                _ => {
+                    unreachable!()
+                }
+            }
+
+            s.alt = Some(alt_of_alt.take());
+        }
+    }
 }

crates/swc_ecma_minifier/src/compress/pure/mod.rs

@@ -459,6 +459,8 @@ impl VisitMut for Pure<'_> {
         s.visit_mut_children_with(self);
 
         self.optimize_expr_in_bool_ctx(&mut s.test, false);
+
+        self.merge_else_if(s);
     }
 
     fn visit_mut_member_expr(&mut self, e: &mut MemberExpr) {

crates/swc_ecma_minifier/tests/postponed.txt

@@ -216,7 +216,6 @@ export/name_cache_mangle_export_default_class/input.js
 export/name_cache_mangle_export_default_function/input.js
 export/name_cache_mangle_local_import_and_export_aliases/input.js
 functions/duplicate_arg_var/input.js
-functions/empty_body/input.js
 functions/hoist_funs/input.js
 functions/hoist_funs_strict/input.js
 functions/inline_1/input.js

crates/swc_ecma_minifier/tests/terser/compress/functions/empty_body/output.js

@@ -1,4 +1,3 @@
 function f() {
-    function noop() {}
+    return function noop() {};
-    return noop;
 }