Harmony: optimize Math.clz32.

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 71946afe068c625cd3b3343f2457fa8b7fef6330..3f5d78e41abc1bb698a3c76dae22a02379932a9b 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -4123,6 +4123,21 @@ void LCodeGen::DoMathLog(LMathLog* instr) {
 }
 
 
+void LCodeGen::DoMathClz32(LMathClz32* instr) {
+  CpuFeatureScope scope(masm(), SSE2);
+  Register input = ToRegister(instr->value());
+  Register result = ToRegister(instr->result());
+  Label not_zero_input;
+  __ bsr(result, input);
+
+  __ j(not_zero, &not_zero_input);
+  __ Set(result, Immediate(63));  // 64^31 == 32

[Sven Panne, 2014/02/19 13:24:08]

63^31=32

+
+  __ bind(&not_zero_input);
+  __ xor_(result, Immediate(31));  // for x in [0..31], 31^x == 31-x.
+}
+
+
 void LCodeGen::DoMathExp(LMathExp* instr) {
   CpuFeatureScope scope(masm(), SSE2);
   XMMRegister input = ToDoubleRegister(instr->value());