Improve checked mode a little (more to come in a different CL).

runtime/vm/intrinsifier_ia32.cc

 // 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.
 //
 // The intrinsic code below is executed before a method has built its frame.
 // The return address is on the stack and the arguments below it.
 // Registers EDX (arguments descriptor) and ECX (function) must be preserved.
 // Each intrinsification method returns true if the corresponding
 // Dart method was intrinsified.
 
@@ skipping 202 matching lines @@
   return false;
 }
 
 
 // Intrinsify only for Smi value and index. Non-smi values need a store buffer
 // update. Array length is always a Smi.
 static bool Array_setIndexed(Assembler* assembler) {
   if (FLAG_enable_type_checks) {
     return false;
   }
-  const Immediate raw_null =
-      Immediate(reinterpret_cast<intptr_t>(Object::null()));
   Label fall_through;
   __ movl(EBX, Address(ESP, + 2 * kWordSize));  // Index.
   __ testl(EBX, Immediate(kSmiTagMask));
   // Index not Smi.
   __ j(NOT_ZERO, &fall_through, Assembler::kNearJump);
   __ movl(EAX, Address(ESP, + 3 * kWordSize));  // Array.
   // Range check.
   __ cmpl(EBX, FieldAddress(EAX, Array::length_offset()));
   // Runtime throws exception.
   __ j(ABOVE_EQUAL, &fall_through, Assembler::kNearJump);
@@ skipping 1011 matching lines @@
   }                                                                            \
 
 INTRINSIC_LIST(FIND_INTRINSICS);
 #undef FIND_INTRINSICS
   return false;
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32