Harmony: optimize Math.clz32.

src/ia32/lithium-codegen-ia32.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4105 matching lines @@
   __ movsd(Operand(esp, 0), input_reg);
   __ fld_d(Operand(esp, 0));
   __ fyl2x();
   __ fstp_d(Operand(esp, 0));
   __ movsd(input_reg, Operand(esp, 0));
   __ add(Operand(esp), Immediate(kDoubleSize));
   __ bind(&done);
 }
 
 
+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));  // 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());
   XMMRegister result = ToDoubleRegister(instr->result());
   XMMRegister temp0 = double_scratch0();
   Register temp1 = ToRegister(instr->temp1());
   Register temp2 = ToRegister(instr->temp2());
 
   MathExpGenerator::EmitMathExp(masm(), input, result, temp0, temp1, temp2);
 }
@@ skipping 2119 matching lines @@
                               FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32