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// Copyright 2017 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_MAP_UPDATER_H_
#define V8_MAP_UPDATER_H_
#include "src/elements-kind.h"
#include "src/field-type.h"
#include "src/globals.h"
#include "src/handles.h"
#include "src/objects/map.h"
#include "src/property-details.h"
namespace v8 {
namespace internal {
// The |MapUpdater| class implements all sorts of map reconfigurations
// including changes of elements kind, property attributes, property kind,
// property location and field representations/type changes. It ensures that
// the reconfigured map and all the intermediate maps are properly integrated
// into the exising transition tree.
//
// To avoid high degrees over polymorphism, and to stabilize quickly, on every
// rewrite the new type is deduced by merging the current type with any
// potential new (partial) version of the type in the transition tree.
// To do this, on each rewrite:
// - Search the root of the transition tree using FindRootMap, remember
// the integrity level (preventExtensions/seal/freeze) transitions.
// - Find/create a |root_map| with requested |new_elements_kind|.
// - Find |target_map|, the newest matching version of this map using the
// "updated" |old_map|'s descriptor array (i.e. whose entry at |modify_index|
// is considered to be of |new_kind| and having |new_attributes|) to walk
// the transition tree. If there was an integrity level transition on the path
// to the old map, use the descriptor array of the map preceding the first
// integrity level transition (|integrity_source_map|), and try to replay
// the integrity level transition afterwards.
// - Merge/generalize the "updated" descriptor array of the |old_map| and
// descriptor array of the |target_map|.
// - Generalize the |modify_index| descriptor using |new_representation| and
// |new_field_type|.
// - Walk the tree again starting from the root towards |target_map|. Stop at
// |split_map|, the first map who's descriptor array does not match the merged
// descriptor array.
// - If |target_map| == |split_map|, and there are no integrity level
// transitions, |target_map| is in the expected state. Return it.
// - Otherwise, invalidate the outdated transition target from |target_map|, and
// replace its transition tree with a new branch for the updated descriptors.
// - If the |old_map| had integrity level transition, create the new map for it.
class MapUpdater {
public:
MapUpdater(Isolate* isolate, Handle<Map> old_map);
// Prepares for reconfiguring of a property at |descriptor| to data field
// with given |attributes| and |representation|/|field_type| and
// performs the steps 1-5.
Handle<Map> ReconfigureToDataField(int descriptor,
PropertyAttributes attributes,
PropertyConstness constness,
Representation representation,
Handle<FieldType> field_type);
// Prepares for reconfiguring elements kind and performs the steps 1-5.
Handle<Map> ReconfigureElementsKind(ElementsKind elements_kind);
// Prepares for updating deprecated map to most up-to-date non-deprecated
// version and performs the steps 1-5.
Handle<Map> Update();
private:
enum State {
kInitialized,
kAtRootMap,
kAtTargetMap,
kAtIntegrityLevelSource,
kEnd
};
// Try to reconfigure property in-place without rebuilding transition tree
// and creating new maps. See implementation for details.
State TryReconfigureToDataFieldInplace();
// Step 1.
// - Search the root of the transition tree using FindRootMap.
// - Find/create a |root_map_| with requested |new_elements_kind_|.
State FindRootMap();
// Step 2.
// - Find |target_map|, the newest matching version of this map using the
// "updated" |old_map|'s descriptor array (i.e. whose entry at
// |modify_index| is considered to be of |new_kind| and having
// |new_attributes|) to walk the transition tree. If there was an integrity
// level transition on the path to the old map, use the descriptor array
// of the map preceding the first integrity level transition
// (|integrity_source_map|), and try to replay the integrity level
// transition afterwards.
State FindTargetMap();
// Step 3.
// - Merge/generalize the "updated" descriptor array of the |old_map_| and
// descriptor array of the |target_map_|.
// - Generalize the |modified_descriptor_| using |new_representation| and
// |new_field_type_|.
Handle<DescriptorArray> BuildDescriptorArray();
// Step 4.
// - Walk the tree again starting from the root towards |target_map|. Stop at
// |split_map|, the first map who's descriptor array does not match the
// merged descriptor array.
Handle<Map> FindSplitMap(Handle<DescriptorArray> descriptors);
// Step 5.
// - If |target_map| == |split_map|, |target_map| is in the expected state.
// Return it.
// - Otherwise, invalidate the outdated transition target from |target_map|,
// and replace its transition tree with a new branch for the updated
// descriptors.
State ConstructNewMap();
// Step 6 (if there was
// - If the |old_map| had integrity level transition, create the new map
// for it.
State ConstructNewMapWithIntegrityLevelTransition();
// When a requested reconfiguration can not be done the result is a copy
// of |old_map_| where every field has |Tagged| representation and |Any|
// field type. This map is disconnected from the transition tree.
State CopyGeneralizeAllFields(const char* reason);
// Returns name of a |descriptor| property.
inline Name GetKey(int descriptor) const;
// Returns property details of a |descriptor| in "updated" |old_descrtiptors_|
// array.
inline PropertyDetails GetDetails(int descriptor) const;
// Returns value of a |descriptor| with kDescriptor location in "updated"
// |old_descrtiptors_| array.
inline Object GetValue(int descriptor) const;
// Returns field type for a |descriptor| with kField location in "updated"
// |old_descrtiptors_| array.
inline FieldType GetFieldType(int descriptor) const;
// If a |descriptor| property in "updated" |old_descriptors_| has kField
// location then returns it's field type otherwise computes optimal field
// type for the descriptor's value and |representation|. The |location|
// value must be a pre-fetched location for |descriptor|.
inline Handle<FieldType> GetOrComputeFieldType(
int descriptor, PropertyLocation location,
Representation representation) const;
// If a |descriptor| property in given |descriptors| array has kField
// location then returns it's field type otherwise computes optimal field
// type for the descriptor's value and |representation|.
// The |location| value must be a pre-fetched location for |descriptor|.
inline Handle<FieldType> GetOrComputeFieldType(
Handle<DescriptorArray> descriptors, int descriptor,
PropertyLocation location, Representation representation);
void GeneralizeField(Handle<Map> map, int modify_index,
PropertyConstness new_constness,
Representation new_representation,
Handle<FieldType> new_field_type);
void SaveIntegrityLevelTransitions();
Isolate* isolate_;
Handle<Map> old_map_;
Handle<DescriptorArray> old_descriptors_;
Handle<Map> root_map_;
Handle<Map> target_map_;
Handle<Map> result_map_;
int old_nof_;
// Information about integrity level transitions.
bool has_integrity_level_transition_ = false;
PropertyAttributes integrity_level_ = NONE;
Handle<Symbol> integrity_level_symbol_;
Handle<Map> integrity_source_map_;
State state_ = kInitialized;
ElementsKind new_elements_kind_;
bool is_transitionable_fast_elements_kind_;
// If |modified_descriptor_| is not equal to -1 then the fields below form
// an "update" of the |old_map_|'s descriptors.
int modified_descriptor_ = -1;
PropertyKind new_kind_ = kData;
PropertyAttributes new_attributes_ = NONE;
PropertyConstness new_constness_ = PropertyConstness::kMutable;
PropertyLocation new_location_ = kField;
Representation new_representation_ = Representation::None();
// Data specific to kField location.
Handle<FieldType> new_field_type_;
// Data specific to kDescriptor location.
Handle<Object> new_value_;
};
} // namespace internal
} // namespace v8
#endif // V8_MAP_UPDATER_H_