VM-codegen: Clean up the way we emit code for comparison instructions.

runtime/vm/constants_x64.h

 // Copyright (c) 2013, 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 RUNTIME_VM_CONSTANTS_X64_H_
 #define RUNTIME_VM_CONSTANTS_X64_H_
 
 namespace dart {
 
 enum Register {
@@ skipping 129 matching lines @@
   LESS = 12,
   GREATER_EQUAL = 13,
   LESS_EQUAL = 14,
   GREATER = 15,
 
   ZERO = EQUAL,
   NOT_ZERO = NOT_EQUAL,
   NEGATIVE = SIGN,
   POSITIVE = NOT_SIGN,
   CARRY = BELOW,
-  NOT_CARRY = ABOVE_EQUAL
+  NOT_CARRY = ABOVE_EQUAL,
+
+  INVALID_CONDITION = 16
 };
 
 #define R(reg) (1 << (reg))
 
 #if defined(_WIN64)
 class CallingConventions {
  public:
   static const Register kArg1Reg = RCX;
   static const Register kArg2Reg = RDX;
   static const Register kArg3Reg = R8;
@@ skipping 71 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  // RUNTIME_VM_CONSTANTS_X64_H_