Fix V8 issue 580: Arithmetic on some integer constants gives wrong anwers.

src/x64/codegen-x64.cc

 // Copyright 2009 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 6187 matching lines @@
   __ bind(&true_result);
   __ movq(rax, Immediate(1));
   __ ret(1 * kPointerSize);
   __ bind(&false_result);
   __ xor_(rax, rax);
   __ ret(1 * kPointerSize);
 }
 
 
 bool CodeGenerator::FoldConstantSmis(Token::Value op, int left, int right) {
-  // TODO(X64): This method is identical to the ia32 version.
-  // Either find a reason to change it, or move it somewhere where it can be
-  // shared. (Notice: It assumes that a Smi can fit in an int).
-
   Object* answer_object = Heap::undefined_value();
   switch (op) {
     case Token::ADD:
-      if (Smi::IsValid(left + right)) {
+      // Use intptr_t to detect overflow of 32-bit int.
+      if (Smi::IsValid(static_cast<intptr_t>(left) + right)) {
         answer_object = Smi::FromInt(left + right);
       }
       break;
     case Token::SUB:
-      if (Smi::IsValid(left - right)) {
+      // Use intptr_t to detect overflow of 32-bit int.
+      if (Smi::IsValid(static_cast<intptr_t>(left) - right)) {
         answer_object = Smi::FromInt(left - right);
       }
       break;
     case Token::MUL: {
         double answer = static_cast<double>(left) * right;
         if (answer >= Smi::kMinValue && answer <= Smi::kMaxValue) {
           // If the product is zero and the non-zero factor is negative,
           // the spec requires us to return floating point negative zero.
           if (answer != 0 || (left + right) >= 0) {
             answer_object = Smi::FromInt(static_cast<int>(answer));
@@ skipping 2146 matching lines @@
   // Call the function from C++.
   return FUNCTION_CAST<ModuloFunction>(buffer);
 }
 
 #endif
 
 
 #undef __
 
 } }  // namespace v8::internal