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Diffstat (limited to 'deps/v8/src/map-updater.h')
| -rw-r--r-- | deps/v8/src/map-updater.h | 173 |
1 files changed, 173 insertions, 0 deletions
diff --git a/deps/v8/src/map-updater.h b/deps/v8/src/map-updater.h new file mode 100644 index 0000000000..68b720365b --- /dev/null +++ b/deps/v8/src/map-updater.h @@ -0,0 +1,173 @@ +// 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_RECONFIGURER_H_ +#define V8_MAP_RECONFIGURER_H_ + +#include "src/elements-kind.h" +#include "src/globals.h" +#include "src/handles.h" +#include "src/objects.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. +// - 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. +// - 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|, |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 +// - Otherwise, invalidate the outdated transition target from |target_map|, and +// replace its transition tree with a new branch for the updated descriptors. +class MapUpdater { + public: + MapUpdater(Isolate* isolate, Handle<Map> old_map) + : isolate_(isolate), + old_map_(old_map), + old_descriptors_(old_map->instance_descriptors(), isolate_), + old_nof_(old_map_->NumberOfOwnDescriptors()), + new_elements_kind_(old_map_->elements_kind()) {} + + // 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, + 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, kEnd }; + + // Try to reconfigure property in-place without rebuilding transition tree + // and creating new maps. See implementation for details. + State TryRecofigureToDataFieldInplace(); + + // 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 + // |modified_descriptor_| is considered to be of |new_kind| and having + // |new_attributes|) to walk the transition tree. + 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(); + + // 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); + + 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_; + + State state_ = kInitialized; + ElementsKind new_elements_kind_; + + // If |modified_descriptor_| is not equal to -1 them the fields below form + // an "update" of the |old_map_|'s descriptors. + int modified_descriptor_ = -1; + PropertyKind new_kind_ = kData; + PropertyAttributes new_attributes_ = NONE; + 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_RECONFIGURER_H_ |