From 904beef6d2dbc7efd4da27e688e841eac564e2e2 Mon Sep 17 00:00:00 2001
From: Andreas Kling <andreas@ladybird.org>
Date: Thu, 27 Mar 2025 14:44:04 +0000
Subject: [PATCH] LibJS: Put newly instantiated functions into locals more
 efficiently

- Don't allocate a separate register, store directly into the local.
- Mark the local as initialized to avoid emitting TDZ checks.
---
 Libraries/LibJS/Bytecode/Generator.cpp | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/Libraries/LibJS/Bytecode/Generator.cpp b/Libraries/LibJS/Bytecode/Generator.cpp
index 19daee2b2bf..25b0c72ce1f 100644
--- a/Libraries/LibJS/Bytecode/Generator.cpp
+++ b/Libraries/LibJS/Bytecode/Generator.cpp
@@ -207,11 +207,14 @@ CodeGenerationErrorOr<void> Generator::emit_function_declaration_instantiation(E
     }
 
     for (auto const& declaration : function.m_functions_to_initialize) {
-        auto function = allocate_register();
-        emit<Op::NewFunction>(function, declaration, OptionalNone {});
-        if (declaration.name_identifier()->is_local()) {
-            emit<Op::Mov>(local(declaration.name_identifier()->local_variable_index()), function);
+        auto const& identifier = *declaration.name_identifier();
+        if (identifier.is_local()) {
+            auto local_index = identifier.local_variable_index();
+            emit<Op::NewFunction>(local(local_index), declaration, OptionalNone {});
+            set_local_initialized(local_index);
         } else {
+            auto function = allocate_register();
+            emit<Op::NewFunction>(function, declaration, OptionalNone {});
             emit<Op::SetVariableBinding>(intern_identifier(declaration.name()), function);
         }
     }