Fix to allocation stub invalidation: we cannot just remove it as it will be collected even though c…

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 3624 matching lines @@
   if ((idx < 0) || (idx >= Array::Cast(types).Length())) {
     return Type::null();
   }
   type ^= Array::Cast(types).At(idx);
   ASSERT(!type.IsNull());
   return type.raw();
 }
 
 
 void Class::set_allocation_stub(const Code& value) const {
+  // Never clear the stub as it may still be a target, but will be GC-d if
+  // not referenced.
   ASSERT(!value.IsNull());
   ASSERT(raw_ptr()->allocation_stub_ == Code::null());
   StorePointer(&raw_ptr()->allocation_stub_, value.raw());
 }
 
 
-void Class::DisableAllocationStub() const {
+void Class::SwitchAllocationStub() const {
   const Code& alloc_stub = Code::Handle(allocation_stub());
   if (!alloc_stub.IsNull()) {
     CodePatcher::PatchEntry(alloc_stub);
-    StorePointer(&raw_ptr()->allocation_stub_, Code::null());
+    const Code& spare_alloc_stub = Code::Handle(spare_allocation_stub());
+    if (spare_alloc_stub.IsNull()) {
+      StorePointer(&raw_ptr()->allocation_stub_, Code::null());
+    } else {
+      ASSERT(CodePatcher::IsEntryPatched(spare_alloc_stub));
+      CodePatcher::RestoreEntry(spare_alloc_stub);
+      StorePointer(&raw_ptr()->allocation_stub_, spare_alloc_stub.raw());
+    }
+    StorePointer(&raw_ptr()->spare_allocation_stub_, alloc_stub.raw());
   }
 }
 
 
 bool Class::IsFunctionClass() const {
   return raw() == Type::Handle(Type::Function()).type_class();
 }
 
 
 bool Class::IsCanonicalSignatureClass() const {
@@ skipping 16685 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart