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

src/crankshaft/x64/lithium-codegen-x64.cc

Index: src/crankshaft/x64/lithium-codegen-x64.cc
diff --git a/src/crankshaft/x64/lithium-codegen-x64.cc b/src/crankshaft/x64/lithium-codegen-x64.cc
index 493bfd49f43f7e8b6f50de39c3a30055d3ba6365..67776e4ca9a6b25ad74d5b36d55f4f5c6e0850bb 100644
--- a/src/crankshaft/x64/lithium-codegen-x64.cc
+++ b/src/crankshaft/x64/lithium-codegen-x64.cc
@@ -3267,8 +3267,19 @@ void LCodeGen::DoDeferredMathAbsTaggedHeapNumber(LMathAbs* instr) {
   DeoptimizeIf(not_equal, instr, Deoptimizer::kNotAHeapNumber);
 
   Label slow, allocated, done;
-  Register tmp = input_reg.is(rax) ? rcx : rax;
-  Register tmp2 = tmp.is(rcx) ? rdx : input_reg.is(rcx) ? rdx : rcx;
+  uint32_t available_regs = rax.bit() | rcx.bit() | rdx.bit() | rbx.bit();
+  available_regs &= ~input_reg.bit();
+  if (instr->context()->IsRegister()) {
+    // Make sure that the context isn't overwritten in the AllocateHeapNumber
+    // macro below.
+    available_regs &= ~ToRegister(instr->context()).bit();
+  }
+
+  Register tmp =
+      Register::from_code(base::bits::CountTrailingZeros32(available_regs));
+  available_regs &= ~tmp.bit();
+  Register tmp2 =
+      Register::from_code(base::bits::CountTrailingZeros32(available_regs));
 
   // Preserve the value of all registers.
   PushSafepointRegistersScope scope(this);