Harmony: optimize Math.clz32.

src/x64/lithium-codegen-x64.cc

 // Copyright 2013 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 3711 matching lines @@
   __ movsd(Operand(rsp, 0), input_reg);
   __ fld_d(Operand(rsp, 0));
   __ fyl2x();
   __ fstp_d(Operand(rsp, 0));
   __ movsd(input_reg, Operand(rsp, 0));
   __ addq(rsp, Immediate(kDoubleSize));
   __ bind(&done);
 }
 
 
+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));
   ASSERT(instr->HasPointerMap());
 
   Handle<JSFunction> known_function = instr->hydrogen()->known_function();
   if (known_function.is_null()) {
     LPointerMap* pointers = instr->pointer_map();
     SafepointGenerator generator(this, pointers, Safepoint::kLazyDeopt);
     ParameterCount count(instr->arity());
@@ skipping 1822 matching lines @@
                                FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64