[turbofan] Turn Math.clz32 into an inlinable builtin.

src/x64/lithium-codegen-x64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/base/bits.h"
 #include "src/code-factory.h"
@@ skipping 3983 matching lines @@
   __ fstp_d(Operand(rsp, 0));
   __ movsd(input_reg, Operand(rsp, 0));
   __ addp(rsp, Immediate(kDoubleSize));
   __ bind(&done);
 }
 
 
 void LCodeGen::DoMathClz32(LMathClz32* instr) {
   Register input = ToRegister(instr->value());
   Register result = ToRegister(instr->result());
-  Label not_zero_input;
-  __ bsrl(result, input);
 
-  __ j(not_zero, &not_zero_input);
-  __ Set(result, 63);  // 63^31 == 32
-
-  __ bind(&not_zero_input);
-  __ xorl(result, Immediate(31));  // for x in [0..31], 31^x == 31-x.
+  __ Lzcntl(result, input);
 }
 
 
 void LCodeGen::DoInvokeFunction(LInvokeFunction* instr) {
   DCHECK(ToRegister(instr->context()).is(rsi));
   DCHECK(ToRegister(instr->function()).is(rdi));
   DCHECK(instr->HasPointerMap());
 
   Handle<JSFunction> known_function = instr->hydrogen()->known_function();
   if (known_function.is_null()) {
@@ skipping 1917 matching lines @@
   CallRuntime(Runtime::kPushBlockContext, 2, instr);
   RecordSafepoint(Safepoint::kNoLazyDeopt);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64