Fix gc on MIPS (live registers were spilled in reversed order).

runtime/vm/assembler_x64.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_X64)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/heap.h"
@@ skipping 3191 matching lines @@
       XmmRegister xmm_reg = static_cast<XmmRegister>(reg_idx);
       if (RegisterSet::Contains(xmm_register_set, xmm_reg)) {
         movups(Address(RSP, offset), xmm_reg);
         offset += kFpuRegisterSize;
       }
     }
     ASSERT(offset == (xmm_regs_count * kFpuRegisterSize));
   }
 
   // Store general purpose registers with the highest register number at the
-  // lowest address.
+  // lowest address. The order in which the registers are pushed must match the
+  // order in which the registers are encoded in the safe point's stack map.
   for (intptr_t reg_idx = 0; reg_idx < kNumberOfCpuRegisters; ++reg_idx) {
     Register reg = static_cast<Register>(reg_idx);
     if (RegisterSet::Contains(cpu_register_set, reg)) {
       pushq(reg);
     }
   }
 }
 
 
 void Assembler::PopRegisters(intptr_t cpu_register_set,
@@ skipping 625 matching lines @@
 
 
 const char* Assembler::FpuRegisterName(FpuRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfXmmRegisters));
   return xmm_reg_names[reg];
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64