From caf2e675bfb6e28f35b72940bd63350d2aa0ab27 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Thu, 9 May 2024 15:21:24 +0200
Subject: [PATCH] LibJS/Bytecode: Don't emit `GetGlobal undefined`

We know that `undefined` in the global scope is always the proper
undefined value. This commit takes advantage of that by simply emitting
a constant undefined value instead.

Unfortunately we can't be so sure in other scopes.
---
 Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
index 3d795e9fbd4..d66e1af98d2 100644
--- a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
@@ -382,6 +382,10 @@ Bytecode::CodeGenerationErrorOr<Optional<ScopedOperand>> Identifier::generate_by
         return local;
     }
 
+    if (is_global() && m_string == "undefined"sv) {
+        return generator.add_constant(js_undefined());
+    }
+
     auto dst = choose_dst(generator, preferred_dst);
     if (is_global()) {
         generator.emit<Bytecode::Op::GetGlobal>(dst, generator.intern_identifier(m_string), generator.next_global_variable_cache());