CTZ instruction implemented as optional operator.

src/ia32/macro-assembler-ia32.cc

 // Copyright 2012 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.
 
 #if V8_TARGET_ARCH_IA32
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
@@ skipping 2412 matching lines @@
   }
   Label not_zero_src;
   bsr(dst, src);
   j(not_zero, &not_zero_src, Label::kNear);
   Move(dst, Immediate(63));  // 63^31 == 32
   bind(&not_zero_src);
   xor_(dst, Immediate(31));  // for x in [0..31], 31^x == 31-x.
 }
 
 
+void MacroAssembler::Tzcnt(Register dst, const Operand& src) {
+  if (CpuFeatures::IsSupported(BMI1)) {
+    CpuFeatureScope scope(this, BMI1);
+    tzcnt(dst, src);
+    return;
+  }
+  Label not_zero_src;
+  bsf(dst, src);
+  j(not_zero, &not_zero_src, Label::kNear);
+  Move(dst, Immediate(32));  // The result of tzcnt is 32 if src = 0.
+  bind(&not_zero_src);
+}
+
+
 void MacroAssembler::SetCounter(StatsCounter* counter, int value) {
   if (FLAG_native_code_counters && counter->Enabled()) {
     mov(Operand::StaticVariable(ExternalReference(counter)), Immediate(value));
   }
 }
 
 
 void MacroAssembler::IncrementCounter(StatsCounter* counter, int value) {
   DCHECK(value > 0);
   if (FLAG_native_code_counters && counter->Enabled()) {
@@ skipping 682 matching lines @@
   mov(eax, dividend);
   shr(eax, 31);
   add(edx, eax);
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_IA32