Make maps in monomorphic IC stubs weak.

src/ic.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 417 matching lines @@
     info->change_own_type_change_checksum();
   }
   host->set_profiler_ticks(0);
   isolate->runtime_profiler()->NotifyICChanged();
   // TODO(2029): When an optimized function is patched, it would
   // be nice to propagate the corresponding type information to its
   // unoptimized version for the benefit of later inlining.
 }
 
 
+void IC::RegisterWeakMapDependency(Handle<Code> stub) {
+  if (FLAG_collect_maps && FLAG_weak_embedded_maps_in_ic &&
+      stub->can_be_weak_stub()) {
+    ASSERT(!stub->is_weak_stub());
+    MapHandleList maps;
+    stub->FindAllMaps(&maps);
+    if (maps.length() == 1 && stub->IsWeakObjectInIC(*maps.at(0))) {
+      maps.at(0)->AddDependentIC(stub);
+      stub->mark_as_weak_stub();
+    }
+  }
+}
+
+
+void IC::InvalidateMaps(Code* stub) {
+  ASSERT(stub->is_weak_stub());
+  stub->mark_as_invalidated_weak_stub();
+  Isolate* isolate = stub->GetIsolate();
+  Heap* heap = isolate->heap();
+  Object* undefined = heap->undefined_value();
+  int mode_mask = RelocInfo::ModeMask(RelocInfo::EMBEDDED_OBJECT);
+  for (RelocIterator it(stub, mode_mask); !it.done(); it.next()) {
+    RelocInfo::Mode mode = it.rinfo()->rmode();
+    if (mode == RelocInfo::EMBEDDED_OBJECT &&
+        it.rinfo()->target_object()->IsMap()) {
+      it.rinfo()->set_target_object(undefined, SKIP_WRITE_BARRIER);
+    }
+  }
+  CPU::FlushICache(stub->instruction_start(), stub->instruction_size());
+}
+
+
 void IC::Clear(Isolate* isolate, Address address,
     ConstantPoolArray* constant_pool) {
   Code* target = GetTargetAtAddress(address, constant_pool);
 
   // Don't clear debug break inline cache as it will remove the break point.
   if (target->is_debug_stub()) return;
 
   switch (target->kind()) {
     case Code::LOAD_IC:
       return LoadIC::Clear(isolate, address, target, constant_pool);
@@ skipping 2385 matching lines @@
 #undef ADDR
 };
 
 
 Address IC::AddressFromUtilityId(IC::UtilityId id) {
   return IC_utilities[id];
 }
 
 
 } }  // namespace v8::internal