Added a DependentCode field to AllocationSite.

src/code-stubs-hydrogen.cc

Index: src/code-stubs-hydrogen.cc
diff --git a/src/code-stubs-hydrogen.cc b/src/code-stubs-hydrogen.cc
index 3e18138eb2b459bc9b0f56392aae3334d2b643f6..b94301fb6796ffbaabeaafe5721c269fc3267a3d 100644
--- a/src/code-stubs-hydrogen.cc
+++ b/src/code-stubs-hydrogen.cc
@@ -463,14 +463,27 @@ HValue* CodeStubGraphBuilder<CreateAllocationSiteStub>::BuildCodeStub() {
                         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);