Remove remaining uses of null's absolute address from non-IA32.

runtime/vm/stub_code_x64.cc

 // 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.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
@@ skipping 475 matching lines @@
 void StubCode::GenerateDeoptimizeStub(Assembler* assembler) {
   GenerateDeoptimizationSequence(assembler, false);  // Don't preserve RAX.
 }
 
 
 static void GenerateDispatcherCode(Assembler* assembler,
                                    Label* call_target_function) {
   __ Comment("NoSuchMethodDispatch");
   // When lazily generated invocation dispatchers are disabled, the
   // miss-handler may return null.
-  const Immediate& raw_null =
-      Immediate(reinterpret_cast<intptr_t>(Object::null()));
-  __ cmpq(RAX, raw_null);
+  __ CompareObject(RAX, Object::null_object());
   __ j(NOT_EQUAL, call_target_function);
   __ EnterStubFrame();
   // Load the receiver.
   __ movq(RDI, FieldAddress(R10, ArgumentsDescriptor::count_offset()));
   __ movq(RAX, Address(
       RBP, RDI, TIMES_HALF_WORD_SIZE, kParamEndSlotFromFp * kWordSize));
-  __ pushq(raw_null);  // Setup space on stack for result.
+  __ PushObject(Object::null_object());  // Setup space on stack for result.
   __ pushq(RAX);  // Receiver.
   __ pushq(RBX);
   __ pushq(R10);  // Arguments descriptor array.
   __ movq(R10, RDI);
   // EDX: Smi-tagged arguments array length.
   PushArgumentsArray(assembler);
   const intptr_t kNumArgs = 4;
   __ CallRuntime(kInvokeNoSuchMethodDispatcherRuntimeEntry, kNumArgs);
   __ Drop(4);
   __ popq(RAX);  // Return value.
@@ skipping 1607 matching lines @@
 // Result:
 //  RCX: entry point.
 void StubCode::GenerateMegamorphicLookupStub(Assembler* assembler) {
   EmitMegamorphicLookup(assembler, RDI, RBX, RCX);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64