Guard against allocation top overflow in ObjectArray_Allocate intrinsic.

runtime/vm/constants_x64.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_CONSTANTS_X64_H_
 #define VM_CONSTANTS_X64_H_
 
 namespace dart {
 
 enum Register {
@@ skipping 91 matching lines @@
   PARITY_EVEN   = 10,
   PARITY_ODD    = 11,
   LESS          = 12,
   GREATER_EQUAL = 13,
   LESS_EQUAL    = 14,
   GREATER       = 15,
 
   ZERO          = EQUAL,
   NOT_ZERO      = NOT_EQUAL,
   NEGATIVE      = SIGN,
-  POSITIVE      = NOT_SIGN
+  POSITIVE      = NOT_SIGN,
+  CARRY         = BELOW,
+  NOT_CARRY     = ABOVE_EQUAL
 };
 
 
 class Instr {
  public:
   static const uint8_t kHltInstruction = 0xF4;
   // We prefer not to use the int3 instruction since it conflicts with gdb.
   static const uint8_t kBreakPointInstruction = kHltInstruction;
   static const int kBreakPointInstructionSize = 1;
 
@@ skipping 15 matching lines @@
 };
 
 
 // The largest multibyte nop we will emit.  This could go up to 15 if it
 // becomes important to us.
 const int MAX_NOP_SIZE = 8;
 
 }  // namespace dart
 
 #endif  // VM_CONSTANTS_X64_H_