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

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

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_IA32
 
 #include "src/crankshaft/ia32/lithium-codegen-ia32.h"
 
 #include "src/base/bits.h"
 #include "src/code-factory.h"
@@ skipping 3054 matching lines @@
 }
 
 
 void LCodeGen::DoDeferredMathAbsTaggedHeapNumber(LMathAbs* instr) {
   Register input_reg = ToRegister(instr->value());
   __ cmp(FieldOperand(input_reg, HeapObject::kMapOffset),
          factory()->heap_number_map());
   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);
 
   __ mov(tmp, FieldOperand(input_reg, HeapNumber::kExponentOffset));
   // Check the sign of the argument. If the argument is positive, just
   // return it. We do not need to patch the stack since |input| and
   // |result| are the same register and |input| will be restored
   // unchanged by popping safepoint registers.
   __ test(tmp, Immediate(HeapNumber::kSignMask));
@@ skipping 2222 matching lines @@
   __ bind(deferred->exit());
   __ bind(&done);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_IA32