src/third_party/v8/src/compiler/serializer-hints.h

// Copyright 2019 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.

// This file defines the hints classed gathered temporarily by the
// SerializerForBackgroundCompilation while it's analysing the bytecode
// and copying the necessary data to the JSHeapBroker for further usage
// by the reducers that run on the background thread.

#ifndef V8_COMPILER_SERIALIZER_HINTS_H_
#define V8_COMPILER_SERIALIZER_HINTS_H_

#include "src/compiler/functional-list.h"
#include "src/handles/handles.h"
#include "src/zone/zone-containers.h"

namespace v8 {
namespace internal {

class Context;
class Object;
class Map;

namespace compiler {

template <typename T, typename EqualTo>
class FunctionalSet {
 public:
  void Add(T const& elem, Zone* zone) {
    for (auto const& l : data_) {
      if (equal_to(l, elem)) return;
    }
    data_.PushFront(elem, zone);
  }

  void Union(FunctionalSet<T, EqualTo> other, Zone* zone) {
    if (!data_.TriviallyEquals(other.data_)) {
      // Choose the larger side as tail.
      if (data_.Size() < other.data_.Size()) std::swap(data_, other.data_);
      for (auto const& elem : other.data_) Add(elem, zone);
    }
  }

  bool IsEmpty() const { return data_.begin() == data_.end(); }

  // Warning: quadratic time complexity.
  bool Includes(FunctionalSet<T, EqualTo> const& other) const {
    return std::all_of(other.begin(), other.end(), [&](T const& other_elem) {
      return std::any_of(this->begin(), this->end(), [&](T const& this_elem) {
        return equal_to(this_elem, other_elem);
      });
    });
  }
  bool operator==(const FunctionalSet<T, EqualTo>& other) const {
    return this->data_.TriviallyEquals(other.data_) ||
           (this->data_.Size() == other.data_.Size() && this->Includes(other) &&
            other.Includes(*this));
  }
  bool operator!=(const FunctionalSet<T, EqualTo>& other) const {
    return !(*this == other);
  }

  size_t Size() const { return data_.Size(); }

  using iterator = typename FunctionalList<T>::iterator;

  iterator begin() const { return data_.begin(); }
  iterator end() const { return data_.end(); }

 private:
  static EqualTo equal_to;
  FunctionalList<T> data_;
};

template <typename T, typename EqualTo>
EqualTo FunctionalSet<T, EqualTo>::equal_to;

struct VirtualContext {
  unsigned int distance;
  Handle<Context> context;

  VirtualContext(unsigned int distance_in, Handle<Context> context_in)
      : distance(distance_in), context(context_in) {
    CHECK_GT(distance, 0);
  }
  bool operator==(const VirtualContext& other) const {
    return context.equals(other.context) && distance == other.distance;
  }
};

class VirtualClosure;
struct VirtualBoundFunction;

using ConstantsSet = FunctionalSet<Handle<Object>, Handle<Object>::equal_to>;
using VirtualContextsSet =
    FunctionalSet<VirtualContext, std::equal_to<VirtualContext>>;
using MapsSet = FunctionalSet<Handle<Map>, Handle<Map>::equal_to>;
using VirtualClosuresSet =
    FunctionalSet<VirtualClosure, std::equal_to<VirtualClosure>>;
using VirtualBoundFunctionsSet =
    FunctionalSet<VirtualBoundFunction, std::equal_to<VirtualBoundFunction>>;

struct HintsImpl;
class JSHeapBroker;

class Hints {
 public:
  Hints() = default;  // Empty.
  static Hints SingleConstant(Handle<Object> constant, Zone* zone);
  static Hints SingleMap(Handle<Map> map, Zone* zone);

  // For inspection only.
  ConstantsSet constants() const;
  MapsSet maps() const;
  VirtualClosuresSet virtual_closures() const;
  VirtualContextsSet virtual_contexts() const;
  VirtualBoundFunctionsSet virtual_bound_functions() const;

  bool IsEmpty() const;
  bool operator==(Hints const& other) const;
  bool operator!=(Hints const& other) const;

#ifdef ENABLE_SLOW_DCHECKS
  bool Includes(Hints const& other) const;
#endif

  Hints Copy(Zone* zone) const;              // Shallow.
  Hints CopyToParentZone(Zone* zone, JSHeapBroker* broker) const;  // Deep.

  // As an optimization, empty hints can be represented as {impl_} being
  // {nullptr}, i.e., as not having allocated a {HintsImpl} object. As a
  // consequence, some operations need to force allocation prior to doing their
  // job. In particular, backpropagation from a child serialization
  // can only work if the hints were already allocated in the parent zone.
  bool IsAllocated() const { return impl_ != nullptr; }
  void EnsureShareable(Zone* zone) { EnsureAllocated(zone, false); }

  // Make {this} an alias of {other}.
  void Reset(Hints* other, Zone* zone);

  void Merge(Hints const& other, Zone* zone, JSHeapBroker* broker);

  // Destructive updates: if the hints are shared by several registers,
  // then the following updates will be seen by all of them:
  void AddConstant(Handle<Object> constant, Zone* zone, JSHeapBroker* broker);
  void AddMap(Handle<Map> map, Zone* zone, JSHeapBroker* broker,
              bool check_zone_equality = true);
  void AddVirtualClosure(VirtualClosure const& virtual_closure, Zone* zone,
                         JSHeapBroker* broker);
  void AddVirtualContext(VirtualContext const& virtual_context, Zone* zone,
                         JSHeapBroker* broker);
  void AddVirtualBoundFunction(VirtualBoundFunction const& bound_function,
                               Zone* zone, JSHeapBroker* broker);
  void Add(Hints const& other, Zone* zone, JSHeapBroker* broker);

 private:
  friend std::ostream& operator<<(std::ostream&, const Hints& hints);
  HintsImpl* impl_ = nullptr;

  void EnsureAllocated(Zone* zone, bool check_zone_equality = true);

  // Helper for Add and Merge.
  bool Union(Hints const& other);

  static const size_t kMaxHintsSize = 50;
  static_assert(kMaxHintsSize >= 1, "must allow for at least one hint");
};

using HintsVector = ZoneVector<Hints>;

}  // namespace compiler
}  // namespace internal
}  // namespace v8

#endif  // V8_COMPILER_SERIALIZER_HINTS_H_