From a5e1e66abc962eb89598462854ba9b24d450ebb3 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Mon, 4 Mar 2024 10:01:40 +0100
Subject: [PATCH] LibJS/Bytecode: Add fast path for LeftShift with Int32
 operands

---
 Userland/Libraries/LibJS/Bytecode/Interpreter.cpp | 14 ++++++++++++++
 Userland/Libraries/LibJS/Bytecode/Op.h            |  4 ++--
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp b/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
index fbcb89d8fd..271ef250ba 100644
--- a/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
@@ -864,6 +864,20 @@ ThrowCompletionOr<void> RightShift::execute_impl(Bytecode::Interpreter& interpre
     return {};
 }
 
+ThrowCompletionOr<void> LeftShift::execute_impl(Bytecode::Interpreter& interpreter) const
+{
+    auto& vm = interpreter.vm();
+    auto const lhs = interpreter.get(m_lhs);
+    auto const rhs = interpreter.get(m_rhs);
+    if (lhs.is_int32() && rhs.is_int32() && rhs.as_i32() >= 0) {
+        auto const shift_count = static_cast<u32>(rhs.as_i32()) % 32;
+        interpreter.set(m_dst, Value(lhs.as_i32() << shift_count));
+        return {};
+    }
+    interpreter.set(m_dst, TRY(left_shift(vm, lhs, rhs)));
+    return {};
+}
+
 ThrowCompletionOr<void> LessThan::execute_impl(Bytecode::Interpreter& interpreter) const
 {
     auto& vm = interpreter.vm();
diff --git a/Userland/Libraries/LibJS/Bytecode/Op.h b/Userland/Libraries/LibJS/Bytecode/Op.h
index 035010f14a..e63d440334 100644
--- a/Userland/Libraries/LibJS/Bytecode/Op.h
+++ b/Userland/Libraries/LibJS/Bytecode/Op.h
@@ -59,6 +59,7 @@ private:
     O(BitwiseXor, bitwise_xor)                           \
     O(GreaterThan, greater_than)                         \
     O(GreaterThanEquals, greater_than_equals)            \
+    O(LeftShift, left_shift)                             \
     O(LessThan, less_than)                               \
     O(LessThanEquals, less_than_equals)                  \
     O(Mul, mul)                                          \
@@ -75,8 +76,7 @@ private:
     O(LooselyInequals, loosely_inequals)                    \
     O(LooselyEquals, loosely_equals)                        \
     O(StrictlyInequals, strict_inequals)                    \
-    O(StrictlyEquals, strict_equals)                        \
-    O(LeftShift, left_shift)
+    O(StrictlyEquals, strict_equals)
 
 #define JS_DECLARE_COMMON_BINARY_OP(OpTitleCase, op_snake_case)                \
     class OpTitleCase final : public Instruction {                             \