Harmony: optimize Math.clz32.

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index a94dcee2271d2efd696ea09cb3162b18cb87a44d..2ca75841ff58e844fcd16c90ef9d26f7ae4da202 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -3729,6 +3729,20 @@ void LCodeGen::DoMathLog(LMathLog* instr) {
 }
 
 
+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.
+}
+
+
 void LCodeGen::DoInvokeFunction(LInvokeFunction* instr) {
   ASSERT(ToRegister(instr->context()).is(rsi));
   ASSERT(ToRegister(instr->function()).is(rdi));