Merge x64 minus-zero fix (bleeding_edge r5631) to 2.3 branch....

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 1400 matching lines @@
 
     if (negative_zero_ == kIgnoreNegativeZero) {
       __ SmiCompare(rax, Smi::FromInt(0));
       __ j(equal, &done);
     }
 
     // Enter runtime system if the value of the smi is zero
     // to make sure that we switch between 0 and -0.
     // Also enter it if the value of the smi is Smi::kMinValue.
     __ SmiNeg(rax, rax, &done);
-
-    // Either zero or Smi::kMinValue, neither of which become a smi when
-    // negated.
-    if (negative_zero_ == kStrictNegativeZero) {
-      __ SmiCompare(rax, Smi::FromInt(0));
-      __ j(not_equal, &slow);
-      __ Move(rax, Factory::minus_zero_value());
-      __ jmp(&done);
-    } else  {
-      __ jmp(&slow);
-    }
+    __ jmp(&slow);
 
     // Try floating point case.
     __ bind(&try_float);
     __ 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.
     __ movq(rdx, FieldOperand(rax, HeapNumber::kValueOffset));
     __ movq(kScratchRegister, Immediate(0x01));
     __ shl(kScratchRegister, Immediate(63));
@@ skipping 2565 matching lines @@
   // tagged as a small integer.
   __ bind(&runtime);
   __ TailCallRuntime(Runtime::kStringCompare, 2, 1);
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64