On MIPS, keeps Object::null() in a register.

runtime/vm/stub_code_arm.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_ARM)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/compiler.h"
@@ skipping 1577 matching lines @@
 // R1: instantiator type arguments or NULL.
 // R2: cache array.
 // Result in R1: null -> not found, otherwise result (true or false).
 static void GenerateSubtypeNTestCacheStub(Assembler* assembler, int n) {
   ASSERT((1 <= n) && (n <= 3));
   if (n > 1) {
     // Get instance type arguments.
     __ LoadClass(R3, R0, R4);
     // Compute instance type arguments into R4.
     Label has_no_type_arguments;
-    __ LoadImmediate(R4, reinterpret_cast<intptr_t>(Object::null()));
     __ ldr(R5, FieldAddress(R3,
         Class::type_arguments_field_offset_in_words_offset()));
     __ CompareImmediate(R5, Class::kNoTypeArguments);
     __ b(&has_no_type_arguments, EQ);
     __ add(R5, R0, ShifterOperand(R5, LSL, 2));
     __ ldr(R4, FieldAddress(R5, 0));
     __ Bind(&has_no_type_arguments);
   }
   __ LoadClassId(R3, R0);
   // R0: instance.
@@ skipping 294 matching lines @@
   __ Bind(&reference_compare);
   __ cmp(left, ShifterOperand(right));
   __ Bind(&done);
   __ PopList((1 << R0) | (1 << R1) | (1 << R2));
   __ Ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM