src/objects/feedback-vector.h

// Copyright 2014 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_OBJECTS_FEEDBACK_VECTOR_H_
#define V8_OBJECTS_FEEDBACK_VECTOR_H_

#include <vector>

#include "src/base/bit-field.h"
#include "src/base/logging.h"
#include "src/base/macros.h"
#include "src/common/globals.h"
#include "src/objects/elements-kind.h"
#include "src/objects/feedback-cell.h"
#include "src/objects/map.h"
#include "src/objects/maybe-object.h"
#include "src/objects/name.h"
#include "src/objects/type-hints.h"
#include "src/zone/zone-containers.h"

// Has to be the last include (doesn't have include guards):
#include "src/objects/object-macros.h"

namespace v8 {
namespace internal {

class IsCompiledScope;
class FeedbackVectorSpec;

enum class UpdateFeedbackMode {
  kOptionalFeedback,
  kGuaranteedFeedback,
  kNoFeedback,
};

// Which feedback slots to clear in Clear().
enum class ClearBehavior {
  kDefault,
  kClearAll,  // .. also ForIn, CompareOp, BinaryOp.
};

enum class FeedbackSlotKind : uint8_t {
  // This kind means that the slot points to the middle of other slot
  // which occupies more than one feedback vector element.
  // There must be no such slots in the system.
  kInvalid,

  // Sloppy kinds come first, for easy language mode testing.
  kStoreGlobalSloppy,
  kSetNamedSloppy,
  kSetKeyedSloppy,
  kLastSloppyKind = kSetKeyedSloppy,

  // Strict and language mode unaware kinds.
  kCall,
  kLoadProperty,
  kLoadGlobalNotInsideTypeof,
  kLoadGlobalInsideTypeof,
  kLoadKeyed,
  kHasKeyed,
  kStoreGlobalStrict,
  kSetNamedStrict,
  kDefineNamedOwn,
  kDefineKeyedOwn,
  kSetKeyedStrict,
  kStoreInArrayLiteral,
  kBinaryOp,
  kCompareOp,
  kDefineKeyedOwnPropertyInLiteral,
  kLiteral,
  kForIn,
  kInstanceOf,
  kCloneObject,
  kJumpLoop,

  kLast = kJumpLoop  // Always update this if the list above changes.
};

static constexpr int kFeedbackSlotKindCount =
    static_cast<int>(FeedbackSlotKind::kLast) + 1;

using MapAndHandler = std::pair<Handle<Map>, MaybeObjectHandle>;
using MapAndFeedback = std::pair<Handle<Map>, MaybeObjectHandle>;

inline bool IsCallICKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kCall;
}

inline bool IsLoadICKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kLoadProperty;
}

inline bool IsLoadGlobalICKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kLoadGlobalNotInsideTypeof ||
         kind == FeedbackSlotKind::kLoadGlobalInsideTypeof;
}

inline bool IsKeyedLoadICKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kLoadKeyed;
}

inline bool IsKeyedHasICKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kHasKeyed;
}

inline bool IsStoreGlobalICKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kStoreGlobalSloppy ||
         kind == FeedbackSlotKind::kStoreGlobalStrict;
}

inline bool IsSetNamedICKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kSetNamedSloppy ||
         kind == FeedbackSlotKind::kSetNamedStrict;
}

inline bool IsDefineNamedOwnICKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kDefineNamedOwn;
}

inline bool IsDefineKeyedOwnICKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kDefineKeyedOwn;
}

inline bool IsDefineKeyedOwnPropertyInLiteralKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kDefineKeyedOwnPropertyInLiteral;
}

inline bool IsKeyedStoreICKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kSetKeyedSloppy ||
         kind == FeedbackSlotKind::kSetKeyedStrict;
}

inline bool IsStoreInArrayLiteralICKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kStoreInArrayLiteral;
}

inline bool IsGlobalICKind(FeedbackSlotKind kind) {
  return IsLoadGlobalICKind(kind) || IsStoreGlobalICKind(kind);
}

inline bool IsCloneObjectKind(FeedbackSlotKind kind) {
  return kind == FeedbackSlotKind::kCloneObject;
}

inline TypeofMode GetTypeofModeFromSlotKind(FeedbackSlotKind kind) {
  DCHECK(IsLoadGlobalICKind(kind));
  return (kind == FeedbackSlotKind::kLoadGlobalInsideTypeof)
             ? TypeofMode::kInside
             : TypeofMode::kNotInside;
}

inline LanguageMode GetLanguageModeFromSlotKind(FeedbackSlotKind kind) {
  DCHECK(IsSetNamedICKind(kind) || IsDefineNamedOwnICKind(kind) ||
         IsStoreGlobalICKind(kind) || IsKeyedStoreICKind(kind) ||
         IsDefineKeyedOwnICKind(kind));
  static_assert(FeedbackSlotKind::kStoreGlobalSloppy <=
                FeedbackSlotKind::kLastSloppyKind);
  static_assert(FeedbackSlotKind::kSetKeyedSloppy <=
                FeedbackSlotKind::kLastSloppyKind);
  static_assert(FeedbackSlotKind::kSetNamedSloppy <=
                FeedbackSlotKind::kLastSloppyKind);
  return (kind <= FeedbackSlotKind::kLastSloppyKind) ? LanguageMode::kSloppy
                                                     : LanguageMode::kStrict;
}

V8_EXPORT_PRIVATE std::ostream& operator<<(std::ostream& os,
                                           FeedbackSlotKind kind);

using MaybeObjectHandles = std::vector<MaybeObjectHandle>;

class FeedbackMetadata;

#include "torque-generated/src/objects/feedback-vector-tq.inc"

class ClosureFeedbackCellArrayShape final : public AllStatic {
 public:
  static constexpr int kElementSize = kTaggedSize;
  using ElementT = FeedbackCell;
  using CompressionScheme = V8HeapCompressionScheme;
  static constexpr RootIndex kMapRootIndex =
      RootIndex::kClosureFeedbackCellArrayMap;
  static constexpr bool kLengthEqualsCapacity = true;

#define FIELD_LIST(V)                                                   \
  V(kCapacityOffset, kTaggedSize)                                       \
  V(kUnalignedHeaderSize, OBJECT_POINTER_PADDING(kUnalignedHeaderSize)) \
  V(kHeaderSize, 0)
  DEFINE_FIELD_OFFSET_CONSTANTS(HeapObject::kHeaderSize, FIELD_LIST)
#undef FIELD_LIST
};

// ClosureFeedbackCellArray contains feedback cells used when creating closures
// from a function. This is created once the function is compiled and is either
// held by the feedback vector (if allocated) or by the FeedbackCell of the
// closure.
class ClosureFeedbackCellArray
    : public TaggedArrayBase<ClosureFeedbackCellArray,
                             ClosureFeedbackCellArrayShape> {
  using Super =
      TaggedArrayBase<ClosureFeedbackCellArray, ClosureFeedbackCellArrayShape>;
  OBJECT_CONSTRUCTORS(ClosureFeedbackCellArray, Super);

 public:
  NEVER_READ_ONLY_SPACE
  using Shape = ClosureFeedbackCellArrayShape;

  V8_EXPORT_PRIVATE static Handle<ClosureFeedbackCellArray> New(
      Isolate* isolate, Handle<SharedFunctionInfo> shared,
      AllocationType allocation = AllocationType::kYoung);

  DECL_VERIFIER(ClosureFeedbackCellArray)
  DECL_PRINTER(ClosureFeedbackCellArray)
  DECL_CAST(ClosureFeedbackCellArray)

  class BodyDescriptor;
};

class NexusConfig;

// A FeedbackVector has a fixed header followed by an array of feedback slots,
// of length determined by the feedback metadata.
class FeedbackVector
    : public TorqueGeneratedFeedbackVector<FeedbackVector, HeapObject> {
 public:
  NEVER_READ_ONLY_SPACE
  DEFINE_TORQUE_GENERATED_OSR_STATE()
  DEFINE_TORQUE_GENERATED_FEEDBACK_VECTOR_FLAGS()
  static_assert(TieringState::kLastTieringState <= TieringStateBits::kMax);

  static constexpr uint32_t kFlagsMaybeHasTurbofanCode =
      FeedbackVector::MaybeHasTurbofanCodeBit::kMask;
  static constexpr uint32_t kFlagsMaybeHasMaglevCode =
      FeedbackVector::MaybeHasMaglevCodeBit::kMask;
  static constexpr uint32_t kFlagsHasAnyOptimizedCode =
      FeedbackVector::MaybeHasMaglevCodeBit::kMask |
      FeedbackVector::MaybeHasTurbofanCodeBit::kMask;
  static constexpr uint32_t kFlagsTieringStateIsAnyRequested =
      kNoneOrInProgressMask << FeedbackVector::TieringStateBits::kShift;
  static constexpr uint32_t kFlagsLogNextExecution =
      FeedbackVector::LogNextExecutionBit::kMask;

  inline bool is_empty() const;

  DECL_GETTER(metadata, Tagged<FeedbackMetadata>)
  DECL_ACQUIRE_GETTER(metadata, Tagged<FeedbackMetadata>)

  // Forward declare the non-atomic accessors.
  using TorqueGeneratedFeedbackVector::invocation_count;
  using TorqueGeneratedFeedbackVector::set_invocation_count;
  DECL_RELAXED_INT32_ACCESSORS(invocation_count)
  inline void clear_invocation_count(RelaxedStoreTag tag);
  using TorqueGeneratedFeedbackVector::invocation_count_before_stable;
  using TorqueGeneratedFeedbackVector::set_invocation_count_before_stable;
  DECL_UINT8_ACCESSORS(invocation_count_before_stable)

  // The [osr_urgency] controls when OSR is attempted, and is incremented as
  // the function becomes hotter. When the current loop depth is less than the
  // osr_urgency, JumpLoop calls into runtime to attempt OSR optimization.
  static constexpr int kMaxOsrUrgency = 6;
  static_assert(kMaxOsrUrgency <= OsrUrgencyBits::kMax);
  inline int osr_urgency() const;
  inline void set_osr_urgency(int urgency);
  inline void reset_osr_urgency();
  inline void RequestOsrAtNextOpportunity();

  // Whether this vector may contain cached optimized osr code for *any* slot.
  // May diverge from the state of the world; the invariant is that if
  // `maybe_has_(maglev|turbofan)_osr_code` is false, no optimized osr code
  // exists.
  inline bool maybe_has_maglev_osr_code() const;
  inline bool maybe_has_turbofan_osr_code() const;
  inline bool maybe_has_optimized_osr_code() const;
  inline void set_maybe_has_optimized_osr_code(bool value, CodeKind code_kind);

  // The `osr_state` contains the osr_urgency and maybe_has_optimized_osr_code.
  inline void reset_osr_state();

  inline Tagged<Code> optimized_code(IsolateForSandbox isolate) const;
  // Whether maybe_optimized_code contains a cached Code object.
  inline bool has_optimized_code() const;

  inline bool log_next_execution() const;
  inline void set_log_next_execution(bool value = true);
  // Similar to above, but represented internally as a bit that can be
  // efficiently checked by generated code. May lag behind the actual state of
  // the world, thus 'maybe'.
  inline bool maybe_has_maglev_code() const;
  inline void set_maybe_has_maglev_code(bool value);
  inline bool maybe_has_turbofan_code() const;
  inline void set_maybe_has_turbofan_code(bool value);

  void SetOptimizedCode(IsolateForSandbox isolate, Tagged<Code> code);
  void EvictOptimizedCodeMarkedForDeoptimization(
      Isolate* isolate, Tagged<SharedFunctionInfo> shared, const char* reason);
  void ClearOptimizedCode();

  // Optimized OSR'd code is cached in JumpLoop feedback vector slots. The
  // slots either contain a Code object or the ClearedValue.
  inline base::Optional<Tagged<Code>> GetOptimizedOsrCode(Isolate* isolate,
                                                          FeedbackSlot slot);
  void SetOptimizedOsrCode(Isolate* isolate, FeedbackSlot slot,
                           Tagged<Code> code);

  inline TieringState tiering_state() const;
  void set_tiering_state(TieringState state);
  void reset_tiering_state();

  bool osr_tiering_in_progress();
  void set_osr_tiering_in_progress(bool osr_in_progress);

  inline bool interrupt_budget_reset_by_ic_change() const;
  inline void set_interrupt_budget_reset_by_ic_change(bool value);

  void reset_flags();

  // Conversion from a slot to an integer index to the underlying array.
  static int GetIndex(FeedbackSlot slot) { return slot.ToInt(); }

  // Conversion from an integer index to the underlying array to a slot.
  static inline FeedbackSlot ToSlot(intptr_t index);

  inline Tagged<MaybeObject> SynchronizedGet(FeedbackSlot slot) const;
  inline void SynchronizedSet(FeedbackSlot slot, Tagged<MaybeObject> value,
                              WriteBarrierMode mode = UPDATE_WRITE_BARRIER);

  inline Tagged<MaybeObject> Get(FeedbackSlot slot) const;
  inline Tagged<MaybeObject> Get(PtrComprCageBase cage_base,
                                 FeedbackSlot slot) const;

  // Returns the feedback cell at |index| that is used to create the
  // closure.
  inline Handle<FeedbackCell> GetClosureFeedbackCell(Isolate* isolate,
                                                     int index) const;
  inline Tagged<FeedbackCell> closure_feedback_cell(int index) const;

  // Gives access to raw memory which stores the array's data.
  inline MaybeObjectSlot slots_start();

  // Returns slot kind for given slot.
  V8_EXPORT_PRIVATE FeedbackSlotKind GetKind(FeedbackSlot slot) const;
  V8_EXPORT_PRIVATE FeedbackSlotKind GetKind(FeedbackSlot slot,
                                             AcquireLoadTag tag) const;

  V8_EXPORT_PRIVATE static Handle<FeedbackVector> New(
      Isolate* isolate, Handle<SharedFunctionInfo> shared,
      Handle<ClosureFeedbackCellArray> closure_feedback_cell_array,
      Handle<FeedbackCell> parent_feedback_cell,
      IsCompiledScope* is_compiled_scope);

  V8_EXPORT_PRIVATE static Handle<FeedbackVector> NewForTesting(
      Isolate* isolate, const FeedbackVectorSpec* spec);
  V8_EXPORT_PRIVATE static Handle<FeedbackVector>
  NewWithOneBinarySlotForTesting(Zone* zone, Isolate* isolate);
  V8_EXPORT_PRIVATE static Handle<FeedbackVector>
  NewWithOneCompareSlotForTesting(Zone* zone, Isolate* isolate);

#define DEFINE_SLOT_KIND_PREDICATE(Name) \
  bool Name(FeedbackSlot slot) const { return Name##Kind(GetKind(slot)); }

  DEFINE_SLOT_KIND_PREDICATE(IsCallIC)
  DEFINE_SLOT_KIND_PREDICATE(IsGlobalIC)
  DEFINE_SLOT_KIND_PREDICATE(IsLoadIC)
  DEFINE_SLOT_KIND_PREDICATE(IsLoadGlobalIC)
  DEFINE_SLOT_KIND_PREDICATE(IsKeyedLoadIC)
  DEFINE_SLOT_KIND_PREDICATE(IsSetNamedIC)
  DEFINE_SLOT_KIND_PREDICATE(IsDefineNamedOwnIC)
  DEFINE_SLOT_KIND_PREDICATE(IsStoreGlobalIC)
  DEFINE_SLOT_KIND_PREDICATE(IsKeyedStoreIC)
#undef DEFINE_SLOT_KIND_PREDICATE

  // Returns typeof mode encoded into kind of given slot.
  inline TypeofMode GetTypeofMode(FeedbackSlot slot) const {
    return GetTypeofModeFromSlotKind(GetKind(slot));
  }

  // Returns language mode encoded into kind of given slot.
  inline LanguageMode GetLanguageMode(FeedbackSlot slot) const {
    return GetLanguageModeFromSlotKind(GetKind(slot));
  }

  DECL_PRINTER(FeedbackVector)

  void FeedbackSlotPrint(std::ostream& os, FeedbackSlot slot);

#ifdef V8_TRACE_FEEDBACK_UPDATES
  static void TraceFeedbackChange(Isolate* isolate,
                                  Tagged<FeedbackVector> vector,
                                  FeedbackSlot slot, const char* reason);
#endif

  // Clears the vector slots. Return true if feedback has changed.
  bool ClearSlots(Isolate* isolate) {
    return ClearSlots(isolate, ClearBehavior::kDefault);
  }
  // As above, but clears *all* slots - even those that we usually keep (e.g.:
  // BinaryOp feedback).
  bool ClearAllSlotsForTesting(Isolate* isolate) {
    return ClearSlots(isolate, ClearBehavior::kClearAll);
  }

  // The object that indicates an uninitialized cache.
  static inline Handle<Symbol> UninitializedSentinel(Isolate* isolate);

  // The object that indicates a megamorphic state.
  static inline Handle<Symbol> MegamorphicSentinel(Isolate* isolate);

  // The object that indicates a MegaDOM state.
  static inline Handle<Symbol> MegaDOMSentinel(Isolate* isolate);

  // A raw version of the uninitialized sentinel that's safe to read during
  // garbage collection (e.g., for patching the cache).
  static inline Tagged<Symbol> RawUninitializedSentinel(Isolate* isolate);

  static_assert(kHeaderSize % kObjectAlignment == 0,
                "Header must be padded for alignment");

  class BodyDescriptor;

  static constexpr int OffsetOfElementAt(int index) {
    return kRawFeedbackSlotsOffset + index * kTaggedSize;
  }

  TQ_OBJECT_CONSTRUCTORS(FeedbackVector)

 private:
  bool ClearSlots(Isolate* isolate, ClearBehavior behavior);

  static void AddToVectorsForProfilingTools(Isolate* isolate,
                                            Handle<FeedbackVector> vector);

  // Private for initializing stores in FeedbackVector::New().
  inline void Set(FeedbackSlot slot, Tagged<MaybeObject> value,
                  WriteBarrierMode mode = UPDATE_WRITE_BARRIER);

#ifdef DEBUG
  // Returns true if value is a non-HashTable FixedArray. We want to
  // make sure not to store such objects in the vector.
  inline static bool IsOfLegacyType(Tagged<MaybeObject> value);
#endif  // DEBUG

  // NexusConfig controls setting slots in the vector.
  friend NexusConfig;

  // Don't expose the raw feedback slot getter/setter.
  using TorqueGeneratedFeedbackVector::raw_feedback_slots;
};

class V8_EXPORT_PRIVATE FeedbackVectorSpec {
 public:
  explicit FeedbackVectorSpec(Zone* zone) : slot_kinds_(zone) {
    slot_kinds_.reserve(16);
  }

  int slot_count() const { return static_cast<int>(slot_kinds_.size()); }
  int create_closure_slot_count() const { return create_closure_slot_count_; }

  int AddCreateClosureSlot() { return create_closure_slot_count_++; }

  FeedbackSlotKind GetKind(FeedbackSlot slot) const {
    return slot_kinds_.at(slot.ToInt());
  }

  FeedbackSlot AddCallICSlot() { return AddSlot(FeedbackSlotKind::kCall); }

  FeedbackSlot AddLoadICSlot() {
    return AddSlot(FeedbackSlotKind::kLoadProperty);
  }

  FeedbackSlot AddLoadGlobalICSlot(TypeofMode typeof_mode) {
    return AddSlot(typeof_mode == TypeofMode::kInside
                       ? FeedbackSlotKind::kLoadGlobalInsideTypeof
                       : FeedbackSlotKind::kLoadGlobalNotInsideTypeof);
  }

  FeedbackSlot AddKeyedLoadICSlot() {
    return AddSlot(FeedbackSlotKind::kLoadKeyed);
  }

  FeedbackSlot AddKeyedHasICSlot() {
    return AddSlot(FeedbackSlotKind::kHasKeyed);
  }

  FeedbackSlotKind GetStoreICSlot(LanguageMode language_mode) {
    static_assert(LanguageModeSize == 2);
    return is_strict(language_mode) ? FeedbackSlotKind::kSetNamedStrict
                                    : FeedbackSlotKind::kSetNamedSloppy;
  }

  FeedbackSlot AddStoreICSlot(LanguageMode language_mode) {
    return AddSlot(GetStoreICSlot(language_mode));
  }

  FeedbackSlot AddDefineNamedOwnICSlot() {
    return AddSlot(FeedbackSlotKind::kDefineNamedOwn);
  }

  // Similar to DefinedNamedOwn, but will throw if a private field already
  // exists.
  FeedbackSlot AddDefineKeyedOwnICSlot() {
    return AddSlot(FeedbackSlotKind::kDefineKeyedOwn);
  }

  FeedbackSlot AddStoreGlobalICSlot(LanguageMode language_mode) {
    static_assert(LanguageModeSize == 2);
    return AddSlot(is_strict(language_mode)
                       ? FeedbackSlotKind::kStoreGlobalStrict
                       : FeedbackSlotKind::kStoreGlobalSloppy);
  }

  FeedbackSlotKind GetKeyedStoreICSlotKind(LanguageMode language_mode) {
    static_assert(LanguageModeSize == 2);
    return is_strict(language_mode) ? FeedbackSlotKind::kSetKeyedStrict
                                    : FeedbackSlotKind::kSetKeyedSloppy;
  }

  FeedbackSlot AddKeyedStoreICSlot(LanguageMode language_mode) {
    return AddSlot(GetKeyedStoreICSlotKind(language_mode));
  }

  FeedbackSlot AddStoreInArrayLiteralICSlot() {
    return AddSlot(FeedbackSlotKind::kStoreInArrayLiteral);
  }

  FeedbackSlot AddBinaryOpICSlot() {
    return AddSlot(FeedbackSlotKind::kBinaryOp);
  }

  FeedbackSlot AddCompareICSlot() {
    return AddSlot(FeedbackSlotKind::kCompareOp);
  }

  FeedbackSlot AddForInSlot() { return AddSlot(FeedbackSlotKind::kForIn); }

  FeedbackSlot AddInstanceOfSlot() {
    return AddSlot(FeedbackSlotKind::kInstanceOf);
  }

  FeedbackSlot AddLiteralSlot() { return AddSlot(FeedbackSlotKind::kLiteral); }

  FeedbackSlot AddDefineKeyedOwnPropertyInLiteralICSlot() {
    return AddSlot(FeedbackSlotKind::kDefineKeyedOwnPropertyInLiteral);
  }

  FeedbackSlot AddCloneObjectSlot() {
    return AddSlot(FeedbackSlotKind::kCloneObject);
  }

  FeedbackSlot AddJumpLoopSlot() {
    return AddSlot(FeedbackSlotKind::kJumpLoop);
  }

#ifdef OBJECT_PRINT
  // For gdb debugging.
  void Print();
#endif  // OBJECT_PRINT

  DECL_PRINTER(FeedbackVectorSpec)

 private:
  FeedbackSlot AddSlot(FeedbackSlotKind kind);

  void append(FeedbackSlotKind kind) { slot_kinds_.push_back(kind); }

  static_assert(sizeof(FeedbackSlotKind) == sizeof(uint8_t));
  ZoneVector<FeedbackSlotKind> slot_kinds_;
  int create_closure_slot_count_ = 0;

  friend class SharedFeedbackSlot;
};

// Helper class that creates a feedback slot on-demand.
class SharedFeedbackSlot {
 public:
  // FeedbackSlot default constructor constructs an invalid slot.
  SharedFeedbackSlot(FeedbackVectorSpec* spec, FeedbackSlotKind kind)
      : kind_(kind), spec_(spec) {}

  FeedbackSlot Get() {
    if (slot_.IsInvalid()) slot_ = spec_->AddSlot(kind_);
    return slot_;
  }

 private:
  FeedbackSlotKind kind_;
  FeedbackSlot slot_;
  FeedbackVectorSpec* spec_;
};

// FeedbackMetadata is an array-like object with a slot count (indicating how
// many slots are stored). We save space by packing several slots into an array
// of int32 data. The length is never stored - it is always calculated from
// slot_count. All instances are created through the static New function, and
// the number of slots is static once an instance is created.
class FeedbackMetadata : public HeapObject {
 public:
  DECL_CAST(FeedbackMetadata)

  // The number of slots that this metadata contains. Stored as an int32.
  DECL_INT32_ACCESSORS(slot_count)

  // The number of feedback cells required for create closures. Stored as an
  // int32.
  // TODO(mythria): Consider using 16 bits for this and slot_count so that we
  // can save 4 bytes.
  DECL_INT32_ACCESSORS(create_closure_slot_count)

  // Get slot_count using an acquire load.
  inline int32_t slot_count(AcquireLoadTag) const;

  // Returns number of feedback vector elements used by given slot kind.
  static inline int GetSlotSize(FeedbackSlotKind kind);

  bool SpecDiffersFrom(const FeedbackVectorSpec* other_spec) const;

  inline bool is_empty() const;

  // Returns slot kind for given slot.
  V8_EXPORT_PRIVATE FeedbackSlotKind GetKind(FeedbackSlot slot) const;

  // If {spec} is null, then it is considered empty.
  template <typename IsolateT>
  V8_EXPORT_PRIVATE static Handle<FeedbackMetadata> New(
      IsolateT* isolate, const FeedbackVectorSpec* spec = nullptr);

  DECL_PRINTER(FeedbackMetadata)
  DECL_VERIFIER(FeedbackMetadata)

  static const char* Kind2String(FeedbackSlotKind kind);

  // Garbage collection support.
  // This includes any necessary padding at the end of the object for pointer
  // size alignment.
  static int SizeFor(int slot_count) {
    return OBJECT_POINTER_ALIGN(kHeaderSize + length(slot_count) * kInt32Size);
  }

#define FIELDS(V)                              \
  V(kSlotCountOffset, kInt32Size)              \
  V(kCreateClosureSlotCountOffset, kInt32Size) \
  V(kHeaderSize, 0)

  DEFINE_FIELD_OFFSET_CONSTANTS(HeapObject::kHeaderSize, FIELDS)
#undef FIELDS

  class BodyDescriptor;

 private:
  friend class AccessorAssembler;

  // Raw accessors to the encoded slot data.
  inline int32_t get(int index) const;
  inline void set(int index, int32_t value);

  // The number of int32 data fields needed to store {slot_count} slots.
  // Does not include any extra padding for pointer size alignment.
  static int length(int slot_count) {
    return VectorICComputer::word_count(slot_count);
  }
  inline int length() const;

  static const int kFeedbackSlotKindBits = 5;
  static_assert(kFeedbackSlotKindCount <= (1 << kFeedbackSlotKindBits));

  void SetKind(FeedbackSlot slot, FeedbackSlotKind kind);

  using VectorICComputer =
      base::BitSetComputer<FeedbackSlotKind, kFeedbackSlotKindBits,
                           kInt32Size * kBitsPerByte, uint32_t>;

  OBJECT_CONSTRUCTORS(FeedbackMetadata, HeapObject);
};

// Verify that an empty hash field looks like a tagged object, but can't
// possibly be confused with a pointer.
static_assert((Name::kEmptyHashField & kHeapObjectTag) == kHeapObjectTag);
static_assert(Name::kEmptyHashField == 0x3);
// Verify that a set hash field will not look like a tagged object.
static_assert(Name::kHashNotComputedMask == kHeapObjectTag);

class FeedbackMetadataIterator {
 public:
  explicit FeedbackMetadataIterator(Handle<FeedbackMetadata> metadata)
      : metadata_handle_(metadata),
        next_slot_(FeedbackSlot(0)),
        slot_kind_(FeedbackSlotKind::kInvalid) {}

  explicit FeedbackMetadataIterator(Tagged<FeedbackMetadata> metadata)
      : metadata_(metadata),
        next_slot_(FeedbackSlot(0)),
        slot_kind_(FeedbackSlotKind::kInvalid) {}

  inline bool HasNext() const;

  inline FeedbackSlot Next();

  // Returns slot kind of the last slot returned by Next().
  FeedbackSlotKind kind() const {
    DCHECK_NE(FeedbackSlotKind::kInvalid, slot_kind_);
    return slot_kind_;
  }

  // Returns entry size of the last slot returned by Next().
  inline int entry_size() const;

 private:
  Tagged<FeedbackMetadata> metadata() const {
    return !metadata_handle_.is_null() ? *metadata_handle_ : metadata_;
  }

  // The reason for having a handle and a raw pointer to the meta data is
  // to have a single iterator implementation for both "handlified" and raw
  // pointer use cases.
  Handle<FeedbackMetadata> metadata_handle_;
  Tagged<FeedbackMetadata> metadata_;
  FeedbackSlot cur_slot_;
  FeedbackSlot next_slot_;
  FeedbackSlotKind slot_kind_;
};

// NexusConfig adapts the FeedbackNexus to be used on the main thread
// or a background thread. It controls the actual read and writes of
// the underlying feedback vector, manages the creation of handles, and
// expresses capabilities available in the very different contexts of
// main and background thread. Here are the differences:
//
// Capability:      MainThread           BackgroundThread
// Write to vector  Allowed              Not allowed
// Handle creation  Via Isolate          Via LocalHeap
// Reads of vector  "Live"               Cached after initial read
// Thread safety    Exclusive write,     Shared read only
//                  shared read
class V8_EXPORT_PRIVATE NexusConfig {
 public:
  static NexusConfig FromMainThread(Isolate* isolate) {
    return NexusConfig(isolate);
  }

  static NexusConfig FromBackgroundThread(Isolate* isolate,
                                          LocalHeap* local_heap) {
    return NexusConfig(isolate, local_heap);
  }

  enum Mode { MainThread, BackgroundThread };

  Mode mode() const {
    return local_heap_ == nullptr ? MainThread : BackgroundThread;
  }

  Isolate* isolate() const { return isolate_; }

  MaybeObjectHandle NewHandle(Tagged<MaybeObject> object) const;
  template <typename T>
  Handle<T> NewHandle(Tagged<T> object) const;

  bool can_write() const { return mode() == MainThread; }

  inline Tagged<MaybeObject> GetFeedback(Tagged<FeedbackVector> vector,
                                         FeedbackSlot slot) const;
  inline void SetFeedback(Tagged<FeedbackVector> vector, FeedbackSlot slot,
                          Tagged<MaybeObject> object,
                          WriteBarrierMode mode = UPDATE_WRITE_BARRIER) const;

  std::pair<Tagged<MaybeObject>, Tagged<MaybeObject>> GetFeedbackPair(
      Tagged<FeedbackVector> vector, FeedbackSlot slot) const;
  void SetFeedbackPair(Tagged<FeedbackVector> vector, FeedbackSlot start_slot,
                       Tagged<MaybeObject> feedback, WriteBarrierMode mode,
                       Tagged<MaybeObject> feedback_extra,
                       WriteBarrierMode mode_extra) const;

 private:
  explicit NexusConfig(Isolate* isolate)
      : isolate_(isolate), local_heap_(nullptr) {}
  NexusConfig(Isolate* isolate, LocalHeap* local_heap)
      : isolate_(isolate), local_heap_(local_heap) {}

  Isolate* const isolate_;
  LocalHeap* const local_heap_;
};

// A FeedbackNexus is the combination of a FeedbackVector and a slot.
class V8_EXPORT_PRIVATE FeedbackNexus final {
 public:
  // For use on the main thread. A null {vector} is accepted as well.
  FeedbackNexus(Handle<FeedbackVector> vector, FeedbackSlot slot);
  FeedbackNexus(Tagged<FeedbackVector> vector, FeedbackSlot slot);

  // For use on the main or background thread as configured by {config}.
  // {vector} must be valid.
  FeedbackNexus(Handle<FeedbackVector> vector, FeedbackSlot slot,
                const NexusConfig& config);

  const NexusConfig* config() const { return &config_; }
  Handle<FeedbackVector> vector_handle() const {
    DCHECK(vector_.is_null());
    return vector_handle_;
  }
  Tagged<FeedbackVector> vector() const {
    return vector_handle_.is_null() ? vector_ : *vector_handle_;
  }

  FeedbackSlot slot() const { return slot_; }
  FeedbackSlotKind kind() const { return kind_; }

  inline LanguageMode GetLanguageMode() const {
    return vector()->GetLanguageMode(slot());
  }

  InlineCacheState ic_state() const;
  bool IsUninitialized() const {
    return ic_state() == InlineCacheState::UNINITIALIZED;
  }
  bool IsMegamorphic() const {
    return ic_state() == InlineCacheState::MEGAMORPHIC;
  }
  bool IsGeneric() const { return ic_state() == InlineCacheState::GENERIC; }

  void Print(std::ostream& os);

  // For map-based ICs (load, keyed-load, store, keyed-store).
  Tagged<Map> GetFirstMap() const;
  int ExtractMaps(MapHandles* maps) const;
  // Used to obtain maps and the associated handlers stored in the feedback
  // vector. This should be called when we expect only a handler to be stored in
  // the extra feedback. This is used by ICs when updating the handlers.
  using TryUpdateHandler = std::function<MaybeHandle<Map>(Handle<Map>)>;
  int ExtractMapsAndHandlers(
      std::vector<MapAndHandler>* maps_and_handlers,
      TryUpdateHandler map_handler = TryUpdateHandler()) const;
  MaybeObjectHandle FindHandlerForMap(Handle<Map> map) const;
  // Used to obtain maps and the associated feedback stored in the feedback
  // vector. The returned feedback need not be always a handler. It could be a
  // name in the case of StoreDataInPropertyLiteral. This is used by TurboFan to
  // get all the feedback stored in the vector.
  int ExtractMapsAndFeedback(
      std::vector<MapAndFeedback>* maps_and_feedback) const;

  bool IsCleared() const {
    InlineCacheState state = ic_state();
    return !v8_flags.use_ic || state == InlineCacheState::UNINITIALIZED;
  }

  // Clear() returns true if the state of the underlying vector was changed.
  bool Clear(ClearBehavior behavior);
  void ConfigureUninitialized();
  // ConfigureMegamorphic() returns true if the state of the underlying vector
  // was changed. Extra feedback is cleared if the 0 parameter version is used.
  bool ConfigureMegamorphic();
  bool ConfigureMegamorphic(IcCheckType property_type);

  inline Tagged<MaybeObject> GetFeedback() const;
  inline Tagged<MaybeObject> GetFeedbackExtra() const;
  inline std::pair<Tagged<MaybeObject>, Tagged<MaybeObject>> GetFeedbackPair()
      const;

  inline Isolate* GetIsolate() const;

  void ConfigureMonomorphic(Handle<Name> name, Handle<Map> receiver_map,
                            const MaybeObjectHandle& handler);

  void ConfigurePolymorphic(
      Handle<Name> name, std::vector<MapAndHandler> const& maps_and_handlers);

  void ConfigureMegaDOM(const MaybeObjectHandle& handler);
  MaybeObjectHandle ExtractMegaDOMHandler();

  BinaryOperationHint GetBinaryOperationFeedback() const;
  CompareOperationHint GetCompareOperationFeedback() const;
  ForInHint GetForInFeedback() const;

  // For KeyedLoad ICs.
  KeyedAccessLoadMode GetKeyedAccessLoadMode() const;

  // For KeyedStore ICs.
  KeyedAccessStoreMode GetKeyedAccessStoreMode() const;

  // For KeyedLoad and KeyedStore ICs.
  IcCheckType GetKeyType() const;
  Tagged<Name> GetName() const;

  // For Call ICs.
  int GetCallCount();
  void SetSpeculationMode(SpeculationMode mode);
  SpeculationMode GetSpeculationMode();
  CallFeedbackContent GetCallFeedbackContent();

  // Compute the call frequency based on the call count and the invocation
  // count (taken from the type feedback vector).
  float ComputeCallFrequency();

  using SpeculationModeField = base::BitField<SpeculationMode, 0, 1>;
  using CallFeedbackContentField = base::BitField<CallFeedbackContent, 1, 1>;
  using CallCountField = base::BitField<uint32_t, 2, 30>;

  // For InstanceOf ICs.
  MaybeHandle<JSObject> GetConstructorFeedback() const;

  // For Global Load and Store ICs.
  void ConfigurePropertyCellMode(Handle<PropertyCell> cell);
  // Returns false if given combination of indices is not allowed.
  bool ConfigureLexicalVarMode(int script_context_index, int context_slot_index,
                               bool immutable);
  void ConfigureHandlerMode(const MaybeObjectHandle& handler);

  // For CloneObject ICs
  static constexpr int kCloneObjectPolymorphicEntrySize = 2;
  void ConfigureCloneObject(Handle<Map> source_map,
                            const MaybeObjectHandle& handler);

// Bit positions in a smi that encodes lexical environment variable access.
#define LEXICAL_MODE_BIT_FIELDS(V, _)  \
  V(ContextIndexBits, unsigned, 12, _) \
  V(SlotIndexBits, unsigned, 18, _)    \
  V(ImmutabilityBit, bool, 1, _)

  DEFINE_BIT_FIELDS(LEXICAL_MODE_BIT_FIELDS)
#undef LEXICAL_MODE_BIT_FIELDS

  // Make sure we don't overflow the smi.
  static_assert(LEXICAL_MODE_BIT_FIELDS_Ranges::kBitsCount <= kSmiValueSize);

 private:
  template <typename FeedbackType>
  inline void SetFeedback(Tagged<FeedbackType> feedback,
                          WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
  template <typename FeedbackType, typename FeedbackExtraType>
  inline void SetFeedback(Tagged<FeedbackType> feedback, WriteBarrierMode mode,
                          Tagged<FeedbackExtraType> feedback_extra,
                          WriteBarrierMode mode_extra = UPDATE_WRITE_BARRIER);

  inline Tagged<MaybeObject> UninitializedSentinel() const;
  inline Tagged<MaybeObject> MegamorphicSentinel() const;
  inline Tagged<MaybeObject> MegaDOMSentinel() const;

  // Create an array. The caller must install it in a feedback vector slot.
  Handle<WeakFixedArray> CreateArrayOfSize(int length);

  // Helpers to maintain feedback_cache_.
  inline Tagged<MaybeObject> FromHandle(MaybeObjectHandle slot) const;
  inline MaybeObjectHandle ToHandle(Tagged<MaybeObject> value) const;

  // The reason for having a vector handle and a raw pointer is that we can and
  // should use handles during IC miss, but not during GC when we clear ICs. If
  // you have a handle to the vector that is better because more operations can
  // be done, like allocation.
  Handle<FeedbackVector> vector_handle_;
  Tagged<FeedbackVector> vector_;
  FeedbackSlot slot_;
  FeedbackSlotKind kind_;
  // When using the background-thread configuration, a cache is used to
  // guarantee a consistent view of the feedback to FeedbackNexus methods.
  mutable base::Optional<std::pair<MaybeObjectHandle, MaybeObjectHandle>>
      feedback_cache_;
  NexusConfig config_;
};

class V8_EXPORT_PRIVATE FeedbackIterator final {
 public:
  explicit FeedbackIterator(const FeedbackNexus* nexus);
  void Advance();
  bool done() { return done_; }
  Tagged<Map> map() { return map_; }
  Tagged<MaybeObject> handler() { return handler_; }

  static int SizeFor(int number_of_entries) {
    CHECK_GT(number_of_entries, 0);
    return number_of_entries * kEntrySize;
  }

  static int MapIndexForEntry(int entry) {
    CHECK_GE(entry, 0);
    return entry * kEntrySize;
  }

  static int HandlerIndexForEntry(int entry) {
    CHECK_GE(entry, 0);
    return (entry * kEntrySize) + kHandlerOffset;
  }

  static constexpr int kEntrySize = 2;
  static constexpr int kHandlerOffset = 1;

 private:
  void AdvancePolymorphic();
  enum State { kMonomorphic, kPolymorphic, kOther };

  Handle<WeakFixedArray> polymorphic_feedback_;
  Tagged<Map> map_;
  Tagged<MaybeObject> handler_;
  bool done_;
  int index_;
  State state_;
};

inline BinaryOperationHint BinaryOperationHintFromFeedback(int type_feedback);
inline CompareOperationHint CompareOperationHintFromFeedback(int type_feedback);
inline ForInHint ForInHintFromFeedback(ForInFeedback type_feedback);

}  // namespace internal
}  // namespace v8

#include "src/objects/object-macros-undef.h"

#endif  // V8_OBJECTS_FEEDBACK_VECTOR_H_