Uses an object pool on x64

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 VM_CONSTANTS_X64_H_
 #define VM_CONSTANTS_X64_H_
 
 namespace dart {
 
 enum Register {
@@ skipping 67 matching lines @@
   REX_B      = 1 << 0,
   REX_X      = 1 << 1,
   REX_R      = 1 << 2,
   REX_W      = 1 << 3,
   REX_PREFIX = 1 << 6
 };
 
 
 // Register aliases.
 const Register TMP = R11;  // Used as scratch register by the assembler.
-const Register CTX = R15;  // Caches current context in generated code.
-const Register PP = kNoRegister;  // No object pool pointer.
+const Register CTX = R14;  // Caches current context in generated code.
+// Caches object pool pointer in generated code.
+const Register PP = R15;
 const Register SPREG = RSP;  // Stack pointer register.
 const Register FPREG = RBP;  // Frame pointer register.
 const Register ICREG = RBX;  // IC data register.
 
 // Exception object is passed in this register to the catch handlers when an
 // exception is thrown.
 const Register kExceptionObjectReg = RAX;
 
 // Stack trace object is passed in this register to the catch handlers when
 // an exception is thrown.
@@ skipping 62 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_