Adapt Danno's Track Allocation Info idea to fast literals. When allocating a literal array,

src/x64/macro-assembler-x64.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1297 matching lines @@
 
   // Activation support.
   void EnterFrame(StackFrame::Type type);
   void LeaveFrame(StackFrame::Type type);
 
   // Expects object in rax and returns map with validated enum cache
   // in rax.  Assumes that any other register can be used as a scratch.
   void CheckEnumCache(Register null_value,
                       Label* call_runtime);
 
+  // AllocationSiteInfo support. Arrays may have an associated
+  // AllocationSiteInfo object that can be checked for in order to pretransition
+  // to another type.
+  // On entry, rdx should point to the array object. rdi gets clobbered.
+  // If allocation info is present, jump to allocation_info_present
+  void PerformAllocationSiteInfoCheck(Label* allocation_info_present);

[danno, 2013/01/04 08:50:55]

Pass in registers

+
  private:
   // Order general registers are pushed by Pushad.
   // rax, rcx, rdx, rbx, rsi, rdi, r8, r9, r11, r14, r15.
   static const int kSafepointPushRegisterIndices[Register::kNumRegisters];
   static const int kNumSafepointSavedRegisters = 11;
   static const int kSmiShift = kSmiTagSize + kSmiShiftSize;
 
   bool generating_stub_;
   bool allow_stub_calls_;
   bool has_frame_;
@@ skipping 156 matching lines @@
     masm->popfq();                                                           \
   }                                                                          \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_