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

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 96f6a460a47e10b52498e93ac73c74e40a15ffec..edfc57a5474bc7c76387b990f24851c061a680b5 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -1315,6 +1315,13 @@ class MacroAssembler: public Assembler {
   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.