Make maps in monomorphic IC stubs weak.

src/ic.cc

Index: src/ic.cc
diff --git a/src/ic.cc b/src/ic.cc
index 36c7e5a30a9f1a1795c54faa2c639b8f6b80f263..8557a2a7e839d9fe00bd84cb5e6109c92ed0f70e 100644
--- a/src/ic.cc
+++ b/src/ic.cc
@@ -435,6 +435,38 @@ void IC::PostPatching(Address address, Code* target, Code* old_target) {
 }
 
 
+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);