LibJS+LibJIT: Add fast path for Int32 * Int32

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/24fb009cf5
Pull-request: https://github.com/SerenityOS/serenity/pull/21672

Userland/Libraries/LibJIT/Assembler.h

@@ -546,6 +546,28 @@ struct Assembler {
         }
     }
 
+    void mul32(Operand dest, Operand src, Optional<Label&> overflow_label)
+    {
+        // imul32 dest, src (32-bit signed)
+        if (dest.type == Operand::Type::Reg && src.type == Operand::Type::Reg) {
+            emit_rex_for_rm(dest, src, REX_W::No);
+            emit8(0x0f);
+            emit8(0xaf);
+            emit_modrm_rm(dest, src);
+        } else if (dest.type == Operand::Type::Reg && src.type == Operand::Type::Mem64BaseAndOffset) {
+            emit_rex_for_rm(dest, src, REX_W::No);
+            emit8(0x0f);
+            emit8(0xaf);
+            emit_modrm_rm(dest, src);
+        } else {
+            VERIFY_NOT_REACHED();
+        }
+
+        if (overflow_label.has_value()) {
+            jump_if(Condition::Overflow, *overflow_label);
+        }
+    }
+
     void enter()
     {
         push(Operand::Register(Reg::RBP));

Userland/Libraries/LibJS/JIT/Compiler.cpp

@@ -578,6 +578,48 @@ void Compiler::compile_sub(Bytecode::Op::Sub const& op)
     end.link(m_assembler);
 }
 
+static Value cxx_mul(VM& vm, Value lhs, Value rhs)
+{
+    return TRY_OR_SET_EXCEPTION(mul(vm, lhs, rhs));
+}
+
+void Compiler::compile_mul(Bytecode::Op::Mul const& op)
+{
+    load_vm_register(ARG1, op.lhs());
+    load_accumulator(ARG2);
+
+    Assembler::Label end {};
+    Assembler::Label slow_case {};
+
+    branch_if_both_int32(ARG1, ARG2, [&] {
+        // GPR0 = ARG1 * ARG2 (32-bit)
+        // if (overflow) goto slow_case;
+        m_assembler.mov(
+            Assembler::Operand::Register(GPR0),
+            Assembler::Operand::Register(ARG1));
+        m_assembler.mul32(
+            Assembler::Operand::Register(GPR0),
+            Assembler::Operand::Register(ARG2),
+            slow_case);
+
+        // accumulator = GPR0 | SHIFTED_INT32_TAG;
+        m_assembler.mov(
+            Assembler::Operand::Register(GPR1),
+            Assembler::Operand::Imm(SHIFTED_INT32_TAG));
+        m_assembler.bitwise_or(
+            Assembler::Operand::Register(GPR0),
+            Assembler::Operand::Register(GPR1));
+        store_accumulator(GPR0);
+        m_assembler.jump(end);
+    });
+
+    slow_case.link(m_assembler);
+    native_call((void*)cxx_mul);
+    store_accumulator(RET);
+    check_exception();
+    end.link(m_assembler);
+}
+
 static Value cxx_less_than(VM& vm, Value lhs, Value rhs)
 {
     return TRY_OR_SET_EXCEPTION(less_than(vm, lhs, rhs));

Userland/Libraries/LibJS/JIT/Compiler.h

@@ -41,7 +41,6 @@ private:
 #    endif
 
 #    define JS_ENUMERATE_COMMON_BINARY_OPS_WITHOUT_FAST_PATH(O) \
-        O(Mul, mul)                                             \
         O(Div, div)                                             \
         O(Exp, exp)                                             \
         O(Mod, mod)                                             \