MIPS: Use neg instruction in r6

src/crankshaft/mips/lithium-codegen-mips.cc

 // Copyright 2012 the V8 project authors. All rights reserved.7
 // 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 3424 matching lines @@
   DoubleRegister result = ToDoubleRegister(instr->result());
   DoubleRegister temp = ToDoubleRegister(instr->temp());
 
   DCHECK(!input.is(result));
 
   // Note that according to ECMA-262 15.8.2.13:
   // Math.pow(-Infinity, 0.5) == Infinity
   // Math.sqrt(-Infinity) == NaN
   Label done;
   __ Move(temp, static_cast<double>(-V8_INFINITY));
+  // Set up Infinity.
   __ Neg_d(result, temp);
+  // result is overwritten if the branch is not taken.
   __ BranchF(&done, NULL, eq, temp, input);
 
   // Add +0 to convert -0 to +0.
   __ add_d(result, input, kDoubleRegZero);
   __ sqrt_d(result, result);
   __ bind(&done);
 }
 
 
 void LCodeGen::DoPower(LPower* instr) {
@@ skipping 2078 matching lines @@
   __ lw(result, FieldMemOperand(scratch,
                                 FixedArray::kHeaderSize - kPointerSize));
   __ bind(deferred->exit());
   __ bind(&done);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8