Added a DependentCode field to AllocationSite.

src/code-stubs-hydrogen.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 445 matching lines @@
   Handle<Map> allocation_site_map(isolate()->heap()->allocation_site_map(),
                                   isolate());
   AddStoreMapConstant(object, allocation_site_map);
 
   // Store the payload (smi elements kind)
   HValue* initial_elements_kind = Add<HConstant>(GetInitialFastElementsKind());
   Add<HStoreNamedField>(object,
                         HObjectAccess::ForAllocationSiteTransitionInfo(),
                         initial_elements_kind);
 
+  // Store an empty fixed array for the code dependency.
+  HConstant* empty_fixed_array =
+    Add<HConstant>(isolate()->factory()->empty_fixed_array());
+  ASSERT(!isolate()->heap()->InNewSpace(
+      isolate()->heap()->empty_fixed_array()));

[Hannes Payer (out of office), 2013/09/19 13:57:08]

This assert can go, empty fixed array is always in old space.

[mvstanton, 2013/09/19 14:06:11]

Done.

+  HStoreNamedField* store = Add<HStoreNamedField>(
+      object,
+      HObjectAccess::ForAllocationSiteDependentCode(),
+      empty_fixed_array);
+  // TODO(mvstanton): Can I improve on using SkipWriteBarrier()? Should the
+  // empty fixed array be an "immortal immovable?"

[Hannes Payer (out of office), 2013/09/19 13:57:08]

The write barrier should be skipped there by default. We can verify if you like?

[mvstanton, 2013/09/19 14:06:11]

I did verify, it was there, but now I've added the empty fixed array to the
immortal immovable list, yay! So the SkipWriteBarrier is removed.

+  store->SkipWriteBarrier();
+
   // Link the object to the allocation site list
   HValue* site_list = Add<HConstant>(
       ExternalReference::allocation_sites_list_address(isolate()));
   HValue* site = Add<HLoadNamedField>(site_list,
                                       HObjectAccess::ForAllocationSiteList());
-  HStoreNamedField* store =
-      Add<HStoreNamedField>(object, HObjectAccess::ForAllocationSiteWeakNext(),
-                            site);
+  store = Add<HStoreNamedField>(object,
+                                HObjectAccess::ForAllocationSiteWeakNext(),
+                                site);
   store->SkipWriteBarrier();
   Add<HStoreNamedField>(site_list, HObjectAccess::ForAllocationSiteList(),
                         object);
 
   // We use a hammer (SkipWriteBarrier()) to indicate that we know the input
   // cell is really a Cell, and so no write barrier is needed.
   // TODO(mvstanton): Add a debug_code check to verify the input cell is really
   // a cell. (perhaps with a new instruction, HAssert).
   HInstruction* cell = GetParameter(0);
   HObjectAccess access = HObjectAccess::ForCellValue();
@@ skipping 414 matching lines @@
   return value;
 }
 
 
 Handle<Code> ElementsTransitionAndStoreStub::GenerateCode() {
   return DoGenerateCode(this);
 }
 
 
 } }  // namespace v8::internal