Make register allocator to disregard constant computation with no uses.

runtime/vm/assembler_ia32.h

 // Copyright (c) 2012, 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_ASSEMBLER_IA32_H_
 #define VM_ASSEMBLER_IA32_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_ia32.h directly; use assembler.h instead.
 #endif
@@ skipping 391 matching lines @@
 
   void testl(Register reg1, Register reg2);
   void testl(Register reg, const Immediate& imm);
 
   void andl(Register dst, const Immediate& imm);
   void andl(Register dst, Register src);
 
   void orl(Register dst, const Immediate& imm);
   void orl(Register dst, Register src);
 
+  void xorl(Register dst, const Immediate& imm);
   void xorl(Register dst, Register src);
 
   void addl(Register dst, Register src);
   void addl(Register reg, const Immediate& imm);
   void addl(Register reg, const Address& address);
 
   void addl(const Address& address, Register reg);
   void addl(const Address& address, const Immediate& imm);
 
   void adcl(Register dst, Register src);
@@ skipping 234 matching lines @@
 }
 
 
 inline void Assembler::EmitOperandSizeOverride() {
   EmitUint8(0x66);
 }
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_IA32_H_