feat(es/minifier): Improve if_return (#4694)

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

@@ -7,7 +7,10 @@ use swc_ecma_utils::{ExprExt, ExprFactory, StmtExt, StmtLike};
 
 use super::Optimizer;
 use crate::{
-    compress::{optimize::Ctx, util::negate_cost},
+    compress::{
+        optimize::Ctx,
+        util::{negate, negate_cost},
+    },
     mode::Mode,
     DISABLE_BUGGY_PASSES,
 };
@@ -687,6 +690,10 @@ where
         *stmts = new;
     }
 
+    /// if (foo) return bar()
+    /// else baz()
+    ///
+    /// `else` token can be removed from the code above.
     /// if (foo) return bar()
     /// else baz()
     ///
@@ -716,11 +723,22 @@ where
                 Ok(stmt) => match stmt {
                     Stmt::If(IfStmt {
                         span,
-                        test,
+                        mut test,
-                        cons,
+                        mut cons,
-                        alt: Some(alt),
+                        alt: Some(mut alt),
                         ..
                     }) if cons.terminates() => {
+                        if let (
+                            Stmt::Return(ReturnStmt { arg: None, .. }),
+                            Stmt::Decl(Decl::Fn(..)),
+                        ) = (&*cons, &*alt)
+                        {
+                            // I don't know why, but terser behaves differently
+                            negate(&self.expr_ctx, &mut test, true, false);
+
+                            swap(&mut cons, &mut alt);
+                        }
+
                         new_stmts.push(T::from_stmt(Stmt::If(IfStmt {
                             span,
                             test,

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

@@ -193,7 +193,7 @@ impl Pure<'_> {
     where
         T: StmtLike + ModuleItemExt + Take,
     {
-        if !self.options.dead_code {
+        if !self.options.dead_code && !self.options.if_return {
             return;
         }
 

crates/swc_ecma_minifier/tests/TODO.txt

@@ -8,8 +8,6 @@ drop_unused/var_catch_toplevel/input.js
 evaluate/issue_2535_1/input.js
 harmony/array_literal_with_spread_4a/input.js
 inline/dont_inline_funcs_into_default_param_2/input.js
-issue_1052/defun_else_if_return/input.js
-issue_1052/defun_if_return/input.js
 issue_281/inner_var_for_in_1/input.js
 issue_368/collapse/input.js
 nullish/conditional_to_nullish_coalescing_2/input.js

crates/swc_ecma_minifier/tests/golden.txt

@@ -271,6 +271,7 @@ conditionals/issue_1645_1/input.js
 conditionals/issue_1645_2/input.js
 conditionals/issue_2535_2/input.js
 conditionals/issue_2560/input.js
+conditionals/issue_2994/input.js
 conditionals/no_evaluate/input.js
 conditionals/ternary_boolean_alternative/input.js
 conditionals/ternary_boolean_consequent/input.js
@@ -711,6 +712,8 @@ issue_1041/const_pragma/input.js
 issue_1041/not_const/input.js
 issue_1043/issue_1043/input.js
 issue_1044/issue_1044/input.js
+issue_1052/defun_else_if_return/input.js
+issue_1052/defun_if_return/input.js
 issue_1105/Infinity_in_with_scope/input.js
 issue_1105/Infinity_not_in_with_scope/input.js
 issue_1105/with_in_global_scope/input.js

crates/swc_ecma_minifier/tests/postponed.txt

@@ -100,7 +100,6 @@ conditionals/ifs_6/input.js
 conditionals/ifs_same_consequent/input.js
 conditionals/issue_1154/input.js
 conditionals/issue_2535_1/input.js
-conditionals/issue_2994/input.js
 dead_code/dead_code_2_should_warn/input.js
 dead_code/dead_code_2_should_warn_strict/input.js
 dead_code/dead_code_const_annotation/input.js

crates/swc_ecma_minifier/tests/terser/compress/conditionals/issue_2994/output.js

@@ -3,14 +3,13 @@ function f(condition1, condition2, condition3) {
         if (condition2) return aValue;
         {
             const variable1 = "something";
-            if (condition3) {
+            if (!condition3) return;
+            {
                 const variable2 = "else";
                 return anotherValue;
             }
-            return;
         }
     }
 }
-let aValue = 2,
+let aValue = 2, anotherValue = 3;
-    anotherValue = 3;
+for(let i = 0; i < 8; ++i)console.log(f(4 & i, 2 & i, 1 & i));
-for (let i = 0; i < 8; ++i) console.log(f(4 & i, 2 & i, 1 & i));