Do not return the constant singleton float -0.0 from UnaryOpStub, because it ...

src/x64/code-stubs-x64.cc

 // Copyright 2010 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 1395 matching lines @@
   if (op_ == Token::SUB) {
     if (include_smi_code_) {
       // Check whether the value is a smi.
       Label try_float;
       __ JumpIfNotSmi(rax, &try_float);
       if (negative_zero_ == kIgnoreNegativeZero) {
         __ SmiCompare(rax, Smi::FromInt(0));
         __ j(equal, &done);
       }
       __ SmiNeg(rax, rax, &done);
+      __ jmp(&slow);  // zero, if not handled above, and Smi::kMinValue.
 
-      // Either zero or Smi::kMinValue, neither of which become a smi when
-      // negated. We handle negative zero here if required. We always enter
-      // the runtime system if we have Smi::kMinValue.
-      if (negative_zero_ == kStrictNegativeZero) {
-        __ SmiCompare(rax, Smi::FromInt(0));
-        __ j(not_equal, &slow);
-        __ Move(rax, Factory::minus_zero_value());
-        __ jmp(&done);
-      } else  {
-        __ SmiCompare(rax, Smi::FromInt(Smi::kMinValue));
-        __ j(equal, &slow);
-        __ jmp(&done);
-      }
       // Try floating point case.
       __ bind(&try_float);
     } else if (FLAG_debug_code) {
       __ AbortIfSmi(rax);
     }
 
     __ movq(rdx, FieldOperand(rax, HeapObject::kMapOffset));
     __ CompareRoot(rdx, Heap::kHeapNumberMapRootIndex);
     __ j(not_equal, &slow);
     // Operand is a float, negate its value by flipping sign bit.
@@ skipping 2605 matching lines @@
   // tagged as a small integer.
   __ bind(&runtime);
   __ TailCallRuntime(Runtime::kStringCompare, 2, 1);
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64