Background compilation work:

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"  // NOLINT
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/heap.h"
@@ skipping 3313 matching lines @@
         offset += kFpuRegisterSize;
       }
     }
     ASSERT(offset == (xmm_regs_count * kFpuRegisterSize));
     AddImmediate(RSP, Immediate(offset));
   }
 }
 
 
 void Assembler::EnterCallRuntimeFrame(intptr_t frame_space) {
+  Comment("EnterCallRuntimeFrame");
   EnterStubFrame();
 
   // TODO(vegorov): avoid saving FpuTMP, it is used only as scratch.
   PushRegisters(CallingConventions::kVolatileCpuRegisters,
                 CallingConventions::kVolatileXmmRegisters);
 
   ReserveAlignedFrameSpace(frame_space);
 }
 
 
@@ skipping 69 matching lines @@
   if (restore_pp == kRestoreCallerPP) {
     movq(PP, Address(RBP, (kSavedCallerPpSlotFromFp * kWordSize)));
     set_constant_pool_allowed(false);
   }
   LeaveFrame();
 }
 
 
 void Assembler::CheckCodePointer() {
 #ifdef DEBUG
+  Comment("CheckCodePointer");
   Label cid_ok, instructions_ok;
   pushq(RAX);
   LoadClassId(RAX, CODE_REG);
   cmpq(RAX, Immediate(kCodeCid));
   j(EQUAL, &cid_ok);
   int3();
   Bind(&cid_ok);
   {
     const intptr_t kRIPRelativeLeaqSize = 7;
     const intptr_t header_to_entry_offset =
@@ skipping 535 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