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// Copyright 2022 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_HEAP_PRETENURING_HANDLER_H_
#define V8_HEAP_PRETENURING_HANDLER_H_
#include <memory>
#include "src/objects/allocation-site.h"
#include "src/objects/heap-object.h"
#include "src/objects/map.h"
namespace v8 {
namespace internal {
template <typename T>
class GlobalHandleVector;
class Heap;
class PretenuringHandler final {
public:
static constexpr int kInitialFeedbackCapacity = 256;
using PretenuringFeedbackMap =
std::unordered_map<Tagged<AllocationSite>, size_t, Object::Hasher>;
enum FindMementoMode { kForRuntime, kForGC };
explicit PretenuringHandler(Heap* heap);
~PretenuringHandler();
void reset();
// If an object has an AllocationMemento trailing it, return it, otherwise
// return a null AllocationMemento.
template <FindMementoMode mode>
inline Tagged<AllocationMemento> FindAllocationMemento(
Tagged<Map> map, Tagged<HeapObject> object);
// ===========================================================================
// Allocation site tracking. =================================================
// ===========================================================================
// Updates the AllocationSite of a given {object}. The entry (including the
// count) is cached on the local pretenuring feedback.
inline void UpdateAllocationSite(
Tagged<Map> map, Tagged<HeapObject> object,
PretenuringFeedbackMap* pretenuring_feedback);
// Merges local pretenuring feedback into the global one. Note that this
// method needs to be called after evacuation, as allocation sites may be
// evacuated and this method resolves forward pointers accordingly.
void MergeAllocationSitePretenuringFeedback(
const PretenuringFeedbackMap& local_pretenuring_feedback);
// Adds an allocation site to the list of sites to be pretenured during the
// next collection. Added allocation sites are pretenured independent of
// their feedback.
V8_EXPORT_PRIVATE void PretenureAllocationSiteOnNextCollection(
Tagged<AllocationSite> site);
// ===========================================================================
// Pretenuring. ==============================================================
// ===========================================================================
// Pretenuring decisions are made based on feedback collected during new space
// evacuation. Note that between feedback collection and calling this method
// object in old space must not move.
void ProcessPretenuringFeedback(size_t new_space_capacity_before_gc);
// Removes an entry from the global pretenuring storage.
void RemoveAllocationSitePretenuringFeedback(Tagged<AllocationSite> site);
bool HasPretenuringFeedback() const {
return !global_pretenuring_feedback_.empty();
}
V8_EXPORT_PRIVATE static int GetMinMementoCountForTesting();
private:
Heap* const heap_;
// The feedback storage is used to store allocation sites (keys) and how often
// they have been visited (values) by finding a memento behind an object. The
// storage is only alive temporary during a GC. The invariant is that all
// pointers in this map are already fixed, i.e., they do not point to
// forwarding pointers.
PretenuringFeedbackMap global_pretenuring_feedback_;
std::unique_ptr<GlobalHandleVector<AllocationSite>>
allocation_sites_to_pretenure_;
};
} // namespace internal
} // namespace v8
#endif // V8_HEAP_PRETENURING_HANDLER_H_
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