Correctly retain argument value when deopting from Math.round on x64.

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 3586 matching lines @@
 
     __ bind(&done);
   }
 }
 
 
 void LCodeGen::DoMathRound(LMathRound* instr) {
   const XMMRegister xmm_scratch = double_scratch0();
   Register output_reg = ToRegister(instr->result());
   XMMRegister input_reg = ToDoubleRegister(instr->value());
+  XMMRegister input_temp = ToDoubleRegister(instr->temp());
   static int64_t one_half = V8_INT64_C(0x3FE0000000000000);  // 0.5
   static int64_t minus_one_half = V8_INT64_C(0xBFE0000000000000);  // -0.5
 
   Label done, round_to_zero, below_one_half, do_not_compensate, restore;

[Jakob Kummerow, 2014/03/13 12:50:01]

We don't need |restore| anymore. And we don't need |do_not_compensate| either
;-)

   Label::Distance dist = DeoptEveryNTimes() ? Label::kFar : Label::kNear;
   __ movq(kScratchRegister, one_half);
   __ movq(xmm_scratch, kScratchRegister);
   __ ucomisd(xmm_scratch, input_reg);
   __ j(above, &below_one_half, Label::kNear);
 
   // CVTTSD2SI rounds towards zero, since 0.5 <= x, we use floor(0.5 + x).
   __ addsd(xmm_scratch, input_reg);
   __ cvttsd2si(output_reg, xmm_scratch);
   // Overflow is signalled with minint.
   __ cmpl(output_reg, Immediate(0x80000000));
   __ RecordComment("D2I conversion overflow");
   DeoptimizeIf(equal, instr->environment());
   __ jmp(&done, dist);
 
   __ bind(&below_one_half);
   __ movq(kScratchRegister, minus_one_half);
   __ movq(xmm_scratch, kScratchRegister);
   __ ucomisd(xmm_scratch, input_reg);
   __ j(below_equal, &round_to_zero, Label::kNear);
 
   // CVTTSD2SI rounds towards zero, we use ceil(x - (-0.5)) and then
   // compare and compensate.
-  __ movq(kScratchRegister, input_reg);  // Back up input_reg.
-  __ subsd(input_reg, xmm_scratch);
-  __ cvttsd2si(output_reg, input_reg);
+  __ movq(input_temp, input_reg);  // Do not alter input_reg.
+  __ subsd(input_temp, xmm_scratch);
+  __ cvttsd2si(output_reg, input_temp);
   // Catch minint due to overflow, and to prevent overflow when compensating.
   __ cmpl(output_reg, Immediate(0x80000000));
   __ RecordComment("D2I conversion overflow");
   DeoptimizeIf(equal, instr->environment());
 
   __ Cvtlsi2sd(xmm_scratch, output_reg);
-  __ ucomisd(input_reg, xmm_scratch);
-  __ j(equal, &restore, Label::kNear);
+  __ ucomisd(xmm_scratch, input_temp);
+  __ j(equal, &done, dist);
   __ subl(output_reg, Immediate(1));
   // No overflow because we already ruled out minint.
-  __ bind(&restore);
-  __ movq(input_reg, kScratchRegister);  // Restore input_reg.
   __ jmp(&done, dist);
 
   __ bind(&round_to_zero);
   // We return 0 for the input range [+0, 0.5[, or [-0.5, 0.5[ if
   // we can ignore the difference between a result of -0 and +0.
   if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
     __ movq(output_reg, input_reg);
     __ testq(output_reg, output_reg);
     __ RecordComment("Minus zero");
     DeoptimizeIf(negative, instr->environment());
@@ skipping 1980 matching lines @@
                                FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64