Ensure that GenerateStoreFastDoubleElement returns stored value on all paths.

src/x64/stub-cache-x64.cc

 // Copyright 2011 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 3734 matching lines @@
   __ bind(&is_nan);
   // Convert all NaNs to the same canonical NaN value when they are stored in
   // the double array.
   __ Set(kScratchRegister, BitCast<uint64_t>(
       FixedDoubleArray::canonical_not_the_hole_nan_as_double()));
   __ movq(xmm0, kScratchRegister);
   __ jmp(&have_double_value, Label::kNear);
 
   __ bind(&smi_value);
   // Value is a smi. convert to a double and store.
-  __ SmiToInteger32(rax, rax);
-  __ push(rax);
+  // Preserve original value.
+  __ SmiToInteger32(rdx, rax);
+  __ push(rdx);
   __ fild_s(Operand(rsp, 0));
-  __ pop(rax);
+  __ pop(rdx);
   __ SmiToInteger32(rcx, rcx);
   __ fstp_d(FieldOperand(rdi, rcx, times_8, FixedDoubleArray::kHeaderSize));
   __ ret(0);
 
   // Handle store cache miss, replacing the ic with the generic stub.
   __ bind(&miss_force_generic);
   Handle<Code> ic_force_generic =
       masm->isolate()->builtins()->KeyedStoreIC_MissForceGeneric();
   __ jmp(ic_force_generic, RelocInfo::CODE_TARGET);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64