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

src/arm/macro-assembler-arm.cc

 // 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 3865 matching lines @@
   ldr(r2, FieldMemOperand(r2, JSObject::kElementsOffset));
   cmp(r2, empty_fixed_array_value);
   b(ne, call_runtime);
 
   ldr(r2, FieldMemOperand(r1, Map::kPrototypeOffset));
   cmp(r2, null_value);
   b(ne, &next);
 }
 
 
+void MacroAssembler::PerformAllocationSiteInfoCheck(
+    Label* allocation_info_present) {
+  Label no_info_available;
+  // ----------- S t a t e -------------
+  //  -- r2    : receiver

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

Pass in receiver_reg and scratch_reg.

[mvstanton, 2013/01/04 12:07:52]

Done.

+  //  r4 is clobbered.
+  // -----------------------------------
+  ExternalReference new_space_start =
+      ExternalReference::new_space_start(isolate());
+  ExternalReference new_space_allocation_top =
+      ExternalReference::new_space_allocation_top_address(isolate());
+
+  ldr(r4, FieldMemOperand(r2, JSArray::kSize + AllocationSiteInfo::kSize));
+  cmp(r4, Operand(new_space_start));
+  b(lt, &no_info_available);
+  cmp(r4, Operand(new_space_allocation_top));
+  b(hs, &no_info_available);
+  ldr(r4, MemOperand(r4, 0));
+  cmp(r4,
+      Operand(Handle<Map>(isolate()->heap()->
+                               allocation_site_info_map())));

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

nit: formatting above, Operand can be on same line as r4 and
allocation_site_info_map should be indented 4 spaces.

[mvstanton, 2013/01/04 12:07:52]

Done.

+
+  // Use the j/jmp sequence below for debugging, but the j(equal) sequence

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

Keep the sequence below uncommented on this and other platforms, just wrap it in
a if (FLAG_debug_code) {}

[mvstanton, 2013/01/04 12:07:52]

I decided to remove it because debug_code should be for additional checks,
whereas my int3() was just so a developer can stop in a debugger to examine the
generated code. I will think about doing some debug_code work in the next
checkin, which does more extensive things with the AllocationSiteInfo payload.
(I can check if the payload is a smi or object, for example).

+  // for production.
+  // b(not_equal, &no_info_available);
+  // int3();
+  // jmp(allocation_info_present);
+  // or
+  b(eq, allocation_info_present);
+  bind(&no_info_available);
+}
+
+
 #ifdef DEBUG
 bool AreAliased(Register reg1,
                 Register reg2,
                 Register reg3,
                 Register reg4,
                 Register reg5,
                 Register reg6) {
   int n_of_valid_regs = reg1.is_valid() + reg2.is_valid() +
     reg3.is_valid() + reg4.is_valid() + reg5.is_valid() + reg6.is_valid();
 
@@ skipping 46 matching lines @@
 void CodePatcher::EmitCondition(Condition cond) {
   Instr instr = Assembler::instr_at(masm_.pc_);
   instr = (instr & ~kCondMask) | cond;
   masm_.emit(instr);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM