X87: CTZ instruction implemented as optional operator.

src/x87/assembler-x87.cc

Index: src/x87/assembler-x87.cc
diff --git a/src/x87/assembler-x87.cc b/src/x87/assembler-x87.cc
index 323d2434f6750471e96db2b1180fe0a33d7a892f..baadd87206d549e54385ecbfb256a347f8b78b16 100644
--- a/src/x87/assembler-x87.cc
+++ b/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);