LibJS/JIT: Expand `Mul` fast path to double & i32 combinations

Co-authored-by: Stephan Vedder <vedder@mbits.info>

Userland/Libraries/LibJIT/X86_64/Assembler.h

@@ -639,6 +639,18 @@ struct X86_64Assembler {
         }
     }
 
+    void mul(Operand dest, Operand src)
+    {
+        if (dest.type == Operand::Type::FReg && src.type == Operand::Type::FReg) {
+            emit8(0xf2);
+            emit8(0x0f);
+            emit8(0x59);
+            emit_modrm_rm(dest, src);
+        } else {
+            VERIFY_NOT_REACHED();
+        }
+    }
+
     void mul32(Operand dest, Operand src, Optional<Label&> overflow_label)
     {
         // imul32 dest, src (32-bit signed)

Userland/Libraries/LibJS/JIT/Compiler.cpp

@@ -695,36 +695,29 @@ 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);
+    branch_if_both_numbers(
+        ARG1, ARG2,
+        [&](auto lhs, auto rhs, auto& slow_case) {
+            m_assembler.mul32(
+                Assembler::Operand::Register(lhs),
+                Assembler::Operand::Register(rhs),
+                slow_case);
+            return lhs; },
+        [&](auto lhs, auto rhs) {
+            m_assembler.mul(
+                Assembler::Operand::FloatRegister(lhs),
+                Assembler::Operand::FloatRegister(rhs));
+            return lhs; },
+        [&](auto lhs, auto rhs) {
+            m_assembler.mov(
+                Assembler::Operand::Register(ARG1),
+                Assembler::Operand::Register(lhs));
+            m_assembler.mov(
+                Assembler::Operand::Register(ARG2),
+                Assembler::Operand::Register(rhs));
+            native_call((void*)cxx_mul);
+            return RET;
+        });
 }
 
 #    define DO_COMPILE_COMPARISON_OP(TitleCaseName, snake_case_name, AssemblerCondition) \