From ce7c9259243ce68875bf1b8fa4bf2da9f51988c3 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Tue, 14 May 2024 13:15:14 +0200
Subject: [PATCH] LibJS/Bytecode: Allow assignment expression to write directly
 to locals

---
 Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
index a468c9cf8c3..c078fc9ac7b 100644
--- a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
@@ -642,7 +642,12 @@ Bytecode::CodeGenerationErrorOr<Optional<ScopedOperand>> AssignmentExpression::g
         return TRY(m_rhs->generate_bytecode(generator)).value();
     }());
 
-    auto dst = choose_dst(generator, preferred_dst);
+    // OPTIMIZATION: If LHS is a local, we can write the result directly into it.
+    auto dst = [&] {
+        if (lhs.operand().is_local())
+            return lhs;
+        return choose_dst(generator, preferred_dst);
+    }();
 
     switch (m_op) {
     case AssignmentOp::AdditionAssignment: