Make register allocator to disregard constant computation with no uses.

runtime/vm/assembler_x64.cc

 // 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.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/heap.h"
 #include "vm/memory_region.h"
@@ skipping 929 matching lines @@
 
 
 void Assembler::xorq(const Address& dst, Register src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitOperandREX(src, dst, REX_W);
   EmitUint8(0x31);
   EmitOperand(src & 7, dst);
 }
 
 
+void Assembler::xorq(Register dst, const Immediate& imm) {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitRegisterREX(dst, REX_W);
+  EmitComplex(6, Operand(dst), imm);
+}
+
+
 void Assembler::addl(Register dst, Register src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   Operand operand(src);
   EmitOperandREX(dst, operand, REX_NONE);
   EmitUint8(0x03);
   EmitOperand(dst & 7, operand);
 }
 
 
 void Assembler::addq(Register dst, Register src) {
@@ skipping 1008 matching lines @@
 
 const char* Assembler::XmmRegisterName(XmmRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfXmmRegisters));
   return xmm_reg_names[reg];
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64