Fix three bugs with handling negative zero in the optimizing compiler.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
===================================================================
--- src/arm/lithium-codegen-arm.cc	(revision 8868)
+++ src/arm/lithium-codegen-arm.cc	(working copy)
@@ -3014,14 +3014,13 @@
 void LCodeGen::DoMathRound(LUnaryMathOperation* instr) {
   DoubleRegister input = ToDoubleRegister(instr->InputAt(0));
   Register result = ToRegister(instr->result());
-  Register scratch1 = result;
   Register scratch2 = scratch0();

[Kevin Millikin (Chromium), 2011/08/10 12:03:53]

It doesn't really make sense to have scratch2 when there is no scratch1 (and
have it be an alias for scratch0!).  Maybe call it scratch?

[fschneider, 2011/08/10 12:33:16]

Done.

   Label done, check_sign_on_zero;
 
   // Extract exponent bits.
-  __ vmov(scratch1, input.high());
+  __ vmov(result, input.high());
   __ ubfx(scratch2,
-          scratch1,
+          result,
           HeapNumber::kExponentShift,
           HeapNumber::kExponentBits);
 
@@ -3040,15 +3039,15 @@
   DeoptimizeIf(ge, instr->environment());
 
   // Save the original sign for later comparison.
-  __ and_(scratch2, scratch1, Operand(HeapNumber::kSignMask));
+  __ and_(scratch2, result, Operand(HeapNumber::kSignMask));
 
   __ Vmov(double_scratch0(), 0.5);
   __ vadd(input, input, double_scratch0());
 
   // Check sign of the result: if the sign changed, the input
   // value was in ]0.5, 0[ and the result should be -0.
-  __ vmov(scratch1, input.high());
-  __ eor(scratch1, scratch1, Operand(scratch2), SetCC);
+  __ vmov(result, input.high());
+  __ eor(result, result, Operand(scratch2), SetCC);
   if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
     DeoptimizeIf(mi, instr->environment());
   } else {
@@ -3059,7 +3058,7 @@
   __ EmitVFPTruncate(kRoundToMinusInf,
                      double_scratch0().low(),
                      input,
-                     scratch1,
+                     result,
                      scratch2);
   DeoptimizeIf(ne, instr->environment());
   __ vmov(result, double_scratch0().low());
@@ -3069,8 +3068,8 @@
     __ cmp(result, Operand(0));
     __ b(ne, &done);
     __ bind(&check_sign_on_zero);
-    __ vmov(scratch1, input.high());
-    __ tst(scratch1, Operand(HeapNumber::kSignMask));
+    __ vmov(scratch2, input.high());
+    __ tst(scratch2, Operand(HeapNumber::kSignMask));
     DeoptimizeIf(ne, instr->environment());
   }
   __ bind(&done);