Use off-heap data for class check instructions

runtime/vm/assembler_ia32.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_ASSEMBLER_IA32_H_
 #define RUNTIME_VM_ASSEMBLER_IA32_H_
 
 #ifndef RUNTIME_VM_ASSEMBLER_H_
 #error Do not include assembler_ia32.h directly; use assembler.h instead.
 #endif
@@ skipping 742 matching lines @@
    */
   void SmiTag(Register reg) { addl(reg, reg); }
 
   void SmiUntag(Register reg) { sarl(reg, Immediate(kSmiTagSize)); }
 
   void BranchIfNotSmi(Register reg, Label* label) {
     testl(reg, Immediate(kSmiTagMask));
     j(NOT_ZERO, label);
   }
 
+  void BranchIfSmi(Register reg, Label* label) {
+    testl(reg, Immediate(kSmiTagMask));
+    j(ZERO, label);
+  }
+
   void Align(intptr_t alignment, intptr_t offset);
   void Bind(Label* label);
   void Jump(Label* label) { jmp(label); }
 
   // Address of code at offset.
   uword CodeAddress(intptr_t offset) { return buffer_.Address(offset); }
 
   intptr_t CodeSize() const { return buffer_.Size(); }
   intptr_t prologue_offset() const { return prologue_offset_; }
   bool has_single_entry_point() const { return true; }
@@ skipping 229 matching lines @@
 }
 
 
 inline void Assembler::EmitOperandSizeOverride() {
   EmitUint8(0x66);
 }
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_ASSEMBLER_IA32_H_