llvm-project/mlir/lib/Support/StorageUniquer.cpp

//===- StorageUniquer.cpp - Common Storage Class Uniquer --------*- C++ -*-===//
//
// Copyright 2019 The MLIR Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// =============================================================================

#include "mlir/Support/StorageUniquer.h"
#include "mlir/Support/LLVM.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/RWMutex.h"

using namespace mlir;
using namespace mlir::detail;

namespace mlir {
namespace detail {
/// This is the implementation of the StorageUniquer class.
struct StorageUniquerImpl {
  using BaseStorage = StorageUniquer::BaseStorage;
  using StorageAllocator = StorageUniquer::StorageAllocator;

  /// A lookup key for derived instances of storage objects.
  struct LookupKey {
    /// The known derived kind for the storage.
    unsigned kind;

    /// The known hash value of the key.
    unsigned hashValue;

    /// An equality function for comparing with an existing storage instance.
    llvm::function_ref<bool(const BaseStorage *)> isEqual;
  };

  /// A utility wrapper object representing a hashed storage object. This class
  /// contains a storage object and an existing computed hash value.
  struct HashedStorage {
    unsigned hashValue;
    BaseStorage *storage;
  };

  /// Get or create an instance of a complex derived type.
  BaseStorage *
  getOrCreate(unsigned kind, unsigned hashValue,
              llvm::function_ref<bool(const BaseStorage *)> isEqual,
              llvm::function_ref<BaseStorage *(StorageAllocator &)> ctorFn) {
    LookupKey lookupKey{kind, hashValue, isEqual};

    // Check for an existing instance in read-only mode.
    {
      llvm::sys::SmartScopedReader<true> typeLock(mutex);
      auto it = storageTypes.find_as(lookupKey);
      if (it != storageTypes.end())
        return it->storage;
    }

    // Acquire a writer-lock so that we can safely create the new type instance.
    llvm::sys::SmartScopedWriter<true> typeLock(mutex);

    // Check for an existing instance again here, because another writer thread
    // may have already created one.
    auto existing = storageTypes.insert_as({}, lookupKey);
    if (!existing.second)
      return existing.first->storage;

    // Otherwise, construct and initialize the derived storage for this type
    // instance.
    BaseStorage *storage = initializeStorage(kind, ctorFn);
    *existing.first = HashedStorage{hashValue, storage};
    return storage;
  }

  /// Get or create an instance of a simple derived type.
  BaseStorage *
  getOrCreate(unsigned kind,
              llvm::function_ref<BaseStorage *(StorageAllocator &)> ctorFn) {
    // Check for an existing instance in read-only mode.
    {
      llvm::sys::SmartScopedReader<true> typeLock(mutex);
      auto it = simpleTypes.find(kind);
      if (it != simpleTypes.end())
        return it->second;
    }

    // Acquire a writer-lock so that we can safely create the new type instance.
    llvm::sys::SmartScopedWriter<true> typeLock(mutex);

    // Check for an existing instance again here, because another writer thread
    // may have already created one.
    auto &result = simpleTypes[kind];
    if (result)
      return result;

    // Otherwise, create and return a new storage instance.
    return result = initializeStorage(kind, ctorFn);
  }

  /// Erase an instance of a complex derived type.
  void erase(unsigned kind, unsigned hashValue,
             llvm::function_ref<bool(const BaseStorage *)> isEqual,
             llvm::function_ref<void(BaseStorage *)> cleanupFn) {
    LookupKey lookupKey{kind, hashValue, isEqual};

    // Acquire a writer-lock so that we can safely erase the type instance.
    llvm::sys::SmartScopedWriter<true> typeLock(mutex);
    auto existing = storageTypes.find_as(lookupKey);
    if (existing == storageTypes.end())
      return;

    // Cleanup the storage and remove it from the map.
    cleanupFn(existing->storage);
    storageTypes.erase(existing);
  }

  //===--------------------------------------------------------------------===//
  // Instance Storage
  //===--------------------------------------------------------------------===//

  /// Utility to create and initialize a storage instance.
  BaseStorage *initializeStorage(
      unsigned kind,
      llvm::function_ref<BaseStorage *(StorageAllocator &)> ctorFn) {
    BaseStorage *storage = ctorFn(allocator);
    storage->kind = kind;
    return storage;
  }

  /// Storage info for derived TypeStorage objects.
  struct StorageKeyInfo : DenseMapInfo<HashedStorage> {
    static HashedStorage getEmptyKey() {
      return HashedStorage{0, DenseMapInfo<BaseStorage *>::getEmptyKey()};
    }
    static HashedStorage getTombstoneKey() {
      return HashedStorage{0, DenseMapInfo<BaseStorage *>::getTombstoneKey()};
    }

    static unsigned getHashValue(const HashedStorage &key) {
      return key.hashValue;
    }
    static unsigned getHashValue(LookupKey key) { return key.hashValue; }

    static bool isEqual(const HashedStorage &lhs, const HashedStorage &rhs) {
      return lhs.storage == rhs.storage;
    }
    static bool isEqual(const LookupKey &lhs, const HashedStorage &rhs) {
      if (isEqual(rhs, getEmptyKey()) || isEqual(rhs, getTombstoneKey()))
        return false;
      // If the lookup kind matches the kind of the storage, then invoke the
      // equality function on the lookup key.
      return lhs.kind == rhs.storage->getKind() && lhs.isEqual(rhs.storage);
    }
  };

  // Unique types with specific hashing or storage constraints.
  using StorageTypeSet = llvm::DenseSet<HashedStorage, StorageKeyInfo>;
  StorageTypeSet storageTypes;

  // Unique types with just the kind.
  DenseMap<unsigned, BaseStorage *> simpleTypes;

  // Allocator to use when constructing derived type instances.
  StorageUniquer::StorageAllocator allocator;

  // A mutex to keep type uniquing thread-safe.
  llvm::sys::SmartRWMutex<true> mutex;
};
} // end namespace detail
} // namespace mlir

StorageUniquer::StorageUniquer() : impl(new StorageUniquerImpl()) {}
StorageUniquer::~StorageUniquer() {}

/// Implementation for getting/creating an instance of a derived type with
/// complex storage.
auto StorageUniquer::getImpl(
    unsigned kind, unsigned hashValue,
    llvm::function_ref<bool(const BaseStorage *)> isEqual,
    std::function<BaseStorage *(StorageAllocator &)> ctorFn) -> BaseStorage * {
  return impl->getOrCreate(kind, hashValue, isEqual, ctorFn);
}

/// Implementation for getting/creating an instance of a derived type with
/// default storage.
auto StorageUniquer::getImpl(
    unsigned kind, std::function<BaseStorage *(StorageAllocator &)> ctorFn)
    -> BaseStorage * {
  return impl->getOrCreate(kind, ctorFn);
}

/// Implementation for erasing an instance of a derived type with complex
/// storage.
void StorageUniquer::eraseImpl(
    unsigned kind, unsigned hashValue,
    llvm::function_ref<bool(const BaseStorage *)> isEqual,
    std::function<void(BaseStorage *)> cleanupFn) {
  impl->erase(kind, hashValue, isEqual, cleanupFn);
}