From ed696b5725f23ebf4c4ec045421c4fdf142c73fa Mon Sep 17 00:00:00 2001
From: Boshen <1430279+Boshen@users.noreply.github.com>
Date: Thu, 17 Jul 2025 14:04:57 +0000
Subject: [PATCH] fix(minifier): remove more unused assignment expressions
 (#12364)

---
 .../src/peephole/remove_dead_code.rs          |  4 ++++
 .../remove_unused_variable_declaration.rs     | 21 ++++++++++++-------
 tasks/minsize/minsize.snap                    |  8 +++----
 3 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/crates/oxc_minifier/src/peephole/remove_dead_code.rs b/crates/oxc_minifier/src/peephole/remove_dead_code.rs
index 9a4a809e66e89..80d75ad1ca98c 100644
--- a/crates/oxc_minifier/src/peephole/remove_dead_code.rs
+++ b/crates/oxc_minifier/src/peephole/remove_dead_code.rs
@@ -49,6 +49,10 @@ impl<'a> PeepholeOptimizations {
                 self.try_fold_conditional_expression(e, state, ctx)
             }
             Expression::SequenceExpression(e) => self.try_fold_sequence_expression(e, state, ctx),
+            Expression::AssignmentExpression(_) => {
+                self.remove_unused_assignment_expression(expr, state, ctx);
+                None
+            }
             _ => None,
         } {
             *expr = folded_expr;
diff --git a/crates/oxc_minifier/src/peephole/remove_unused_variable_declaration.rs b/crates/oxc_minifier/src/peephole/remove_unused_variable_declaration.rs
index 1ead2df217621..26e671f14d499 100644
--- a/crates/oxc_minifier/src/peephole/remove_unused_variable_declaration.rs
+++ b/crates/oxc_minifier/src/peephole/remove_unused_variable_declaration.rs
@@ -1,6 +1,5 @@
 use oxc_allocator::TakeIn;
 use oxc_ast::ast::*;
-use oxc_ecmascript::side_effects::MayHaveSideEffects;
 
 use crate::{CompressOptionsUnused, ctx::Ctx};
 
@@ -79,13 +78,9 @@ impl<'a> PeepholeOptimizations {
         if !ctx.scoping().get_resolved_references(symbol_id).all(|r| !r.flags().is_read()) {
             return false;
         }
+        *e = assign_expr.right.take_in(ctx.ast);
         state.changed = true;
-        if assign_expr.right.may_have_side_effects(ctx) {
-            *e = assign_expr.right.take_in(ctx.ast);
-            false
-        } else {
-            true
-        }
+        false
     }
 
     /// Do remove top level vars in script mode.
@@ -132,7 +127,17 @@ mod test {
         test_options("var x = 1; x = 2;", "", &options);
         test_options("var x = 1; x = foo();", "foo()", &options);
         test_same_options("var x = 1; x = 2, foo(x)", &options);
-        test_same_options("function foo() { var t; return t = x(); } foo();", &options);
+        test_same_options("function foo() { return t = x(); } foo();", &options);
+        test_options(
+            "function foo() { var t; return t = x(); } foo();",
+            "function foo() { return x(); } foo();",
+            &options,
+        );
+        test_options(
+            "function foo(t) { return t = x(); } foo();",
+            "function foo(t) { return x(); } foo();",
+            &options,
+        );
     }
 
     #[test]
diff --git a/tasks/minsize/minsize.snap b/tasks/minsize/minsize.snap
index cdffd933888cc..f835ace0c522e 100644
--- a/tasks/minsize/minsize.snap
+++ b/tasks/minsize/minsize.snap
@@ -11,17 +11,17 @@ Original   | minified   | minified   | gzip       | gzip       | Fixture
 
 544.10 kB  | 71.38 kB   | 72.48 kB   | 25.85 kB   | 26.20 kB   | lodash.js 
 
-555.77 kB  | 270.82 kB  | 270.13 kB  | 88.25 kB   | 90.80 kB   | d3.js     
+555.77 kB  | 270.80 kB  | 270.13 kB  | 88.24 kB   | 90.80 kB   | d3.js     
 
 1.01 MB    | 440.17 kB  | 458.89 kB  | 122.37 kB  | 126.71 kB  | bundle.min.js
 
 1.25 MB    | 647 kB     | 646.76 kB  | 160.28 kB  | 163.73 kB  | three.js  
 
-2.14 MB    | 716.11 kB  | 724.14 kB  | 161.77 kB  | 181.07 kB  | victory.js
+2.14 MB    | 716.10 kB  | 724.14 kB  | 161.76 kB  | 181.07 kB  | victory.js
 
 3.20 MB    | 1.01 MB    | 1.01 MB    | 324.08 kB  | 331.56 kB  | echarts.js
 
-6.69 MB    | 2.25 MB    | 2.31 MB    | 463.06 kB  | 488.28 kB  | antd.js   
+6.69 MB    | 2.24 MB    | 2.31 MB    | 462.45 kB  | 488.28 kB  | antd.js   
 
-10.95 MB   | 3.35 MB    | 3.49 MB    | 860.92 kB  | 915.50 kB  | typescript.js
+10.95 MB   | 3.34 MB    | 3.49 MB    | 856.90 kB  | 915.50 kB  | typescript.js