[crankshaft] Fix DoDeferredMathAbsTaggedHeapNumber overwriting the context with some temporary valu…

src/crankshaft/ia32/lithium-codegen-ia32.cc

Index: src/crankshaft/ia32/lithium-codegen-ia32.cc
diff --git a/src/crankshaft/ia32/lithium-codegen-ia32.cc b/src/crankshaft/ia32/lithium-codegen-ia32.cc
index 00761c4857a6467208403bd16cb59253dc4fec50..baebe1972655d8a09c0e0f69f18c0fc27e7de910 100644
--- a/src/crankshaft/ia32/lithium-codegen-ia32.cc
+++ b/src/crankshaft/ia32/lithium-codegen-ia32.cc
@@ -3072,8 +3072,20 @@ void LCodeGen::DoDeferredMathAbsTaggedHeapNumber(LMathAbs* instr) {
   DeoptimizeIf(not_equal, instr, Deoptimizer::kNotAHeapNumber);
 
   Label slow, allocated, done;
-  Register tmp = input_reg.is(eax) ? ecx : eax;
-  Register tmp2 = tmp.is(ecx) ? edx : input_reg.is(ecx) ? edx : ecx;
+  uint32_t available_regs = 0xf;

[Jarin, 2016/06/06 08:09:22]

uint32_t available_regs = eax.bit() | ebx.bit() | ecx.bit() | edx.bit();

+  if (input_reg.code() < 4) available_regs ^= input_reg.bit();

[Jarin, 2016/06/06 08:09:22]

available_regs &= ~input_reg.bit();  ?

+  if (instr->context()->IsRegister()) {
+    // Make sure that the context isn't overwritten in the AllocateHeapNumber
+    // macro below.
+    Register context_reg = ToRegister(instr->context());
+    if (context_reg.code() < 4) available_regs ^= context_reg.bit();

[Jarin, 2016/06/06 08:09:21]

available_regs &= ~context_reg.bit();

+  }
+
+  Register tmp =
+      Register::from_code(base::bits::CountTrailingZeros32(available_regs));
+  available_regs ^= tmp.bit();

[Jarin, 2016/06/06 08:09:22]

For consistency, may even here:

DCHECK(available_regs & tmp.bit());
available_regs &= ~tmp.bit();

+  Register tmp2 =
+      Register::from_code(base::bits::CountTrailingZeros32(available_regs));

[Jarin, 2016/06/06 08:09:22]

DCHECK(available_regs & tmp2.bit());

 
   // Preserve the value of all registers.
   PushSafepointRegistersScope scope(this);