From 4ba2eb8fe531094ed783c0267a9603c91dfc645e Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Mon, 7 Jun 2021 15:19:48 +0200
Subject: [PATCH] LibJS: Cache generated bytecode for ScriptFunction

It's silly to generate new bytecode every time you call a function.
Let's just cache the code instead. :^)
---
 .../Libraries/LibJS/Runtime/ScriptFunction.cpp     | 14 ++++++++------
 Userland/Libraries/LibJS/Runtime/ScriptFunction.h  |  1 +
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/Userland/Libraries/LibJS/Runtime/ScriptFunction.cpp b/Userland/Libraries/LibJS/Runtime/ScriptFunction.cpp
index 9447544d407..3a4e83f4cbf 100644
--- a/Userland/Libraries/LibJS/Runtime/ScriptFunction.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ScriptFunction.cpp
@@ -151,13 +151,15 @@ Value ScriptFunction::execute_function_body()
 
     if (bytecode_interpreter) {
         prepare_arguments();
-        auto block = Bytecode::Generator::generate(m_body);
-        VERIFY(block);
-        if constexpr (JS_BYTECODE_DEBUG) {
-            dbgln("Compiled Bytecode::Block for function '{}':", m_name);
-            block->dump();
+        if (!m_bytecode_block) {
+            m_bytecode_block = Bytecode::Generator::generate(m_body);
+            VERIFY(m_bytecode_block);
+            if constexpr (JS_BYTECODE_DEBUG) {
+                dbgln("Compiled Bytecode::Block for function '{}':", m_name);
+                m_bytecode_block->dump();
+            }
         }
-        return bytecode_interpreter->run(*block);
+        return bytecode_interpreter->run(*m_bytecode_block);
     } else {
         OwnPtr<Interpreter> local_interpreter;
         ast_interpreter = vm.interpreter_if_exists();
diff --git a/Userland/Libraries/LibJS/Runtime/ScriptFunction.h b/Userland/Libraries/LibJS/Runtime/ScriptFunction.h
index 3e55cd276d6..d866c788786 100644
--- a/Userland/Libraries/LibJS/Runtime/ScriptFunction.h
+++ b/Userland/Libraries/LibJS/Runtime/ScriptFunction.h
@@ -47,6 +47,7 @@ private:
     FlyString m_name;
     NonnullRefPtr<Statement> m_body;
     const Vector<FunctionNode::Parameter> m_parameters;
+    OwnPtr<Bytecode::Block> m_bytecode_block;
     ScopeObject* m_parent_scope { nullptr };
     i32 m_function_length { 0 };
     bool m_is_strict { false };