X87: CTZ instruction implemented as optional operator.

    port b3334087 (r31313).

    original commit message:

BUG=

Review URL: https://codereview.chromium.org/1412893006

Cr-Commit-Position: refs/heads/master@{#31516}

src/x87/assembler-x87.cc

@@ -1178,6 +1178,14 @@ void Assembler::bsr(Register dst, const Operand& src) {
 }
 
 
+void Assembler::bsf(Register dst, const Operand& src) {
+  EnsureSpace ensure_space(this);
+  EMIT(0x0F);
+  EMIT(0xBC);
+  emit_operand(dst, src);
+}
+
+
 void Assembler::hlt() {
   EnsureSpace ensure_space(this);
   EMIT(0xF4);

src/x87/assembler-x87.h

@@ -771,6 +771,8 @@ class Assembler : public AssemblerBase {
   void bts(const Operand& dst, Register src);
   void bsr(Register dst, Register src) { bsr(dst, Operand(src)); }
   void bsr(Register dst, const Operand& src);
+  void bsf(Register dst, Register src) { bsf(dst, Operand(src)); }
+  void bsf(Register dst, const Operand& src);
 
   // Miscellaneous
   void hlt();

src/x87/macro-assembler-x87.cc

@@ -2317,6 +2317,16 @@ void MacroAssembler::Lzcnt(Register dst, const Operand& src) {
 }
 
 
+void MacroAssembler::Tzcnt(Register dst, const Operand& src) {
+  // TODO(intel): Add support for TZCNT (with ABM/BMI1).
+  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));

src/x87/macro-assembler-x87.h

@@ -809,6 +809,9 @@ class MacroAssembler: public Assembler {
   void Lzcnt(Register dst, Register src) { Lzcnt(dst, Operand(src)); }
   void Lzcnt(Register dst, const Operand& src);
 
+  void Tzcnt(Register dst, Register src) { Tzcnt(dst, Operand(src)); }
+  void Tzcnt(Register dst, const Operand& src);
+
   // Emit call to the code we are currently generating.
   void CallSelf() {
     Handle<Code> self(reinterpret_cast<Code**>(CodeObject().location()));