CTZ instruction implemented as optional operator.

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
diff --git a/src/x64/assembler-x64.cc b/src/x64/assembler-x64.cc
index 059b576beaa42d52765c8b383762199a0a14e392..c7490cb1790ef97140e50eb55820100de6fbc8ab 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -745,6 +745,24 @@ void Assembler::bsrl(Register dst, const Operand& src) {
 }
 
 
+void Assembler::bsfl(Register dst, Register src) {
+  EnsureSpace ensure_space(this);
+  emit_optional_rex_32(dst, src);
+  emit(0x0F);
+  emit(0xBC);
+  emit_modrm(dst, src);
+}
+
+
+void Assembler::bsfl(Register dst, const Operand& src) {
+  EnsureSpace ensure_space(this);
+  emit_optional_rex_32(dst, src);
+  emit(0x0F);
+  emit(0xBC);
+  emit_operand(dst, src);
+}
+
+
 void Assembler::call(Label* L) {
   positions_recorder()->WriteRecordedPositions();
   EnsureSpace ensure_space(this);