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

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//===- StorageUniquer.cpp - Common Storage Class Uniquer ------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "mlir/Support/StorageUniquer.h"
#include "mlir/Support/LLVM.h"
#include "mlir/Support/ThreadLocalCache.h"
#include "mlir/Support/TypeID.h"
#include "llvm/Support/RWMutex.h"
using namespace mlir;
using namespace mlir::detail;
namespace {
/// This class represents a uniquer for storage instances of a specific type
/// that has parametric storage. It contains all of the necessary data to unique
/// storage instances in a thread safe way. This allows for the main uniquer to
/// bucket each of the individual sub-types removing the need to lock the main
/// uniquer itself.
class ParametricStorageUniquer {
public:
using BaseStorage = StorageUniquer::BaseStorage;
using StorageAllocator = StorageUniquer::StorageAllocator;
/// A lookup key for derived instances of storage objects.
struct LookupKey {
/// The known hash value of the key.
unsigned hashValue;
/// An equality function for comparing with an existing storage instance.
function_ref<bool(const BaseStorage *)> isEqual;
};
private:
/// A utility wrapper object representing a hashed storage object. This class
/// contains a storage object and an existing computed hash value.
struct HashedStorage {
HashedStorage(unsigned hashValue = 0, BaseStorage *storage = nullptr)
: hashValue(hashValue), storage(storage) {}
unsigned hashValue;
BaseStorage *storage;
};
/// Storage info for derived TypeStorage objects.
struct StorageKeyInfo {
static inline HashedStorage getEmptyKey() {
return HashedStorage(0, DenseMapInfo<BaseStorage *>::getEmptyKey());
}
static inline HashedStorage getTombstoneKey() {
return HashedStorage(0, DenseMapInfo<BaseStorage *>::getTombstoneKey());
}
static inline unsigned getHashValue(const HashedStorage &key) {
return key.hashValue;
}
static inline unsigned getHashValue(const LookupKey &key) {
return key.hashValue;
}
static inline bool isEqual(const HashedStorage &lhs,
const HashedStorage &rhs) {
return lhs.storage == rhs.storage;
}
static inline bool isEqual(const LookupKey &lhs, const HashedStorage &rhs) {
if (isEqual(rhs, getEmptyKey()) || isEqual(rhs, getTombstoneKey()))
return false;
// Invoke the equality function on the lookup key.
return lhs.isEqual(rhs.storage);
}
};
using StorageTypeSet = DenseSet<HashedStorage, StorageKeyInfo>;
/// This class represents a single shard of the uniquer. The uniquer uses a
/// set of shards to allow for multiple threads to create instances with less
/// lock contention.
struct Shard {
/// The set containing the allocated storage instances.
StorageTypeSet instances;
/// Allocator to use when constructing derived instances.
StorageAllocator allocator;
#if LLVM_ENABLE_THREADS != 0
/// A mutex to keep uniquing thread-safe.
llvm::sys::SmartRWMutex<true> mutex;
#endif
};
/// Get or create an instance of a param derived type in an thread-unsafe
/// fashion.
BaseStorage *
getOrCreateUnsafe(Shard &shard, LookupKey &key,
function_ref<BaseStorage *(StorageAllocator &)> ctorFn) {
auto existing = shard.instances.insert_as({key.hashValue}, key);
BaseStorage *&storage = existing.first->storage;
if (existing.second)
storage = ctorFn(shard.allocator);
return storage;
}
/// Destroy all of the storage instances within the given shard.
void destroyShardInstances(Shard &shard) {
if (!destructorFn)
return;
for (HashedStorage &instance : shard.instances)
destructorFn(instance.storage);
}
public:
#if LLVM_ENABLE_THREADS != 0
/// Initialize the storage uniquer with a given number of storage shards to
/// use. The provided shard number is required to be a valid power of 2. The
/// destructor function is used to destroy any allocated storage instances.
ParametricStorageUniquer(function_ref<void(BaseStorage *)> destructorFn,
size_t numShards = 8)
: shards(new std::atomic<Shard *>[numShards]), numShards(numShards),
destructorFn(destructorFn) {
assert(llvm::isPowerOf2_64(numShards) &&
"the number of shards is required to be a power of 2");
for (size_t i = 0; i < numShards; i++)
shards[i].store(nullptr, std::memory_order_relaxed);
}
~ParametricStorageUniquer() {
// Free all of the allocated shards.
for (size_t i = 0; i != numShards; ++i) {
if (Shard *shard = shards[i].load()) {
destroyShardInstances(*shard);
delete shard;
}
}
}
/// Get or create an instance of a parametric type.
BaseStorage *
getOrCreate(bool threadingIsEnabled, unsigned hashValue,
function_ref<bool(const BaseStorage *)> isEqual,
function_ref<BaseStorage *(StorageAllocator &)> ctorFn) {
Shard &shard = getShard(hashValue);
ParametricStorageUniquer::LookupKey lookupKey{hashValue, isEqual};
if (!threadingIsEnabled)
return getOrCreateUnsafe(shard, lookupKey, ctorFn);
// Check for a instance of this object in the local cache.
auto localIt = localCache->insert_as({hashValue}, lookupKey);
BaseStorage *&localInst = localIt.first->storage;
if (localInst)
return localInst;
// Check for an existing instance in read-only mode.
{
llvm::sys::SmartScopedReader<true> typeLock(shard.mutex);
auto it = shard.instances.find_as(lookupKey);
if (it != shard.instances.end())
return localInst = it->storage;
}
// Acquire a writer-lock so that we can safely create the new storage
// instance.
llvm::sys::SmartScopedWriter<true> typeLock(shard.mutex);
return localInst = getOrCreateUnsafe(shard, lookupKey, ctorFn);
}
/// Run a mutation function on the provided storage object in a thread-safe
/// way.
LogicalResult
mutate(bool threadingIsEnabled, BaseStorage *storage,
function_ref<LogicalResult(StorageAllocator &)> mutationFn) {
Shard &shard = getShardFor(storage);
if (!threadingIsEnabled)
return mutationFn(shard.allocator);
llvm::sys::SmartScopedWriter<true> lock(shard.mutex);
return mutationFn(shard.allocator);
}
private:
/// Return the shard used for the given hash value.
Shard &getShard(unsigned hashValue) {
// Get a shard number from the provided hashvalue.
unsigned shardNum = hashValue & (numShards - 1);
// Try to acquire an already initialized shard.
Shard *shard = shards[shardNum].load(std::memory_order_acquire);
if (shard)
return *shard;
// Otherwise, try to allocate a new shard.
Shard *newShard = new Shard();
if (shards[shardNum].compare_exchange_strong(shard, newShard))
return *newShard;
// If one was allocated before we can initialize ours, delete ours.
delete newShard;
return *shard;
}
/// Return the shard that allocated the provided storage object.
Shard &getShardFor(BaseStorage *storage) {
for (size_t i = 0; i != numShards; ++i) {
if (Shard *shard = shards[i].load(std::memory_order_acquire)) {
llvm::sys::SmartScopedReader<true> lock(shard->mutex);
if (shard->allocator.allocated(storage))
return *shard;
}
}
llvm_unreachable("expected storage object to have a valid shard");
}
/// A thread local cache for storage objects. This helps to reduce the lock
/// contention when an object already existing in the cache.
ThreadLocalCache<StorageTypeSet> localCache;
/// A set of uniquer shards to allow for further bucketing accesses for
/// instances of this storage type. Each shard is lazily initialized to reduce
/// the overhead when only a small amount of shards are in use.
std::unique_ptr<std::atomic<Shard *>[]> shards;
/// The number of available shards.
size_t numShards;
/// Function to used to destruct any allocated storage instances.
function_ref<void(BaseStorage *)> destructorFn;
#else
/// If multi-threading is disabled, ignore the shard parameter as we will
/// always use one shard. The destructor function is used to destroy any
/// allocated storage instances.
ParametricStorageUniquer(function_ref<void(BaseStorage *)> destructorFn,
size_t numShards = 0)
: destructorFn(destructorFn) {}
~ParametricStorageUniquer() { destroyShardInstances(shard); }
/// Get or create an instance of a parametric type.
BaseStorage *
getOrCreate(bool threadingIsEnabled, unsigned hashValue,
function_ref<bool(const BaseStorage *)> isEqual,
function_ref<BaseStorage *(StorageAllocator &)> ctorFn) {
ParametricStorageUniquer::LookupKey lookupKey{hashValue, isEqual};
return getOrCreateUnsafe(shard, lookupKey, ctorFn);
}
/// Run a mutation function on the provided storage object in a thread-safe
/// way.
LogicalResult
mutate(bool threadingIsEnabled, BaseStorage *storage,
function_ref<LogicalResult(StorageAllocator &)> mutationFn) {
return mutationFn(shard.allocator);
}
private:
/// The main uniquer shard that is used for allocating storage instances.
Shard shard;
/// Function to used to destruct any allocated storage instances.
function_ref<void(BaseStorage *)> destructorFn;
#endif
};
} // namespace
namespace mlir {
namespace detail {
/// This is the implementation of the StorageUniquer class.
struct StorageUniquerImpl {
using BaseStorage = StorageUniquer::BaseStorage;
using StorageAllocator = StorageUniquer::StorageAllocator;
//===--------------------------------------------------------------------===//
// Parametric Storage
//===--------------------------------------------------------------------===//
/// Check if an instance of a parametric storage class exists.
bool hasParametricStorage(TypeID id) { return parametricUniquers.count(id); }
/// Get or create an instance of a parametric type.
BaseStorage *
getOrCreate(TypeID id, unsigned hashValue,
function_ref<bool(const BaseStorage *)> isEqual,
function_ref<BaseStorage *(StorageAllocator &)> ctorFn) {
assert(parametricUniquers.count(id) &&
"creating unregistered storage instance");
ParametricStorageUniquer &storageUniquer = *parametricUniquers[id];
return storageUniquer.getOrCreate(threadingIsEnabled, hashValue, isEqual,
ctorFn);
}
/// Run a mutation function on the provided storage object in a thread-safe
/// way.
LogicalResult
mutate(TypeID id, BaseStorage *storage,
function_ref<LogicalResult(StorageAllocator &)> mutationFn) {
assert(parametricUniquers.count(id) &&
"mutating unregistered storage instance");
ParametricStorageUniquer &storageUniquer = *parametricUniquers[id];
return storageUniquer.mutate(threadingIsEnabled, storage, mutationFn);
}
//===--------------------------------------------------------------------===//
// Singleton Storage
//===--------------------------------------------------------------------===//
/// Get or create an instance of a singleton storage class.
BaseStorage *getSingleton(TypeID id) {
BaseStorage *singletonInstance = singletonInstances[id];
assert(singletonInstance && "expected singleton instance to exist");
return singletonInstance;
}
/// Check if an instance of a singleton storage class exists.
bool hasSingleton(TypeID id) const { return singletonInstances.count(id); }
//===--------------------------------------------------------------------===//
// Instance Storage
//===--------------------------------------------------------------------===//
/// Map of type ids to the storage uniquer to use for registered objects.
DenseMap<TypeID, std::unique_ptr<ParametricStorageUniquer>>
parametricUniquers;
/// Map of type ids to a singleton instance when the storage class is a
/// singleton.
DenseMap<TypeID, BaseStorage *> singletonInstances;
/// Allocator used for uniquing singleton instances.
StorageAllocator singletonAllocator;
/// Flag specifying if multi-threading is enabled within the uniquer.
bool threadingIsEnabled = true;
};
} // namespace detail
} // namespace mlir
StorageUniquer::StorageUniquer() : impl(new StorageUniquerImpl()) {}
StorageUniquer::~StorageUniquer() = default;
/// Set the flag specifying if multi-threading is disabled within the uniquer.
void StorageUniquer::disableMultithreading(bool disable) {
impl->threadingIsEnabled = !disable;
}
/// Implementation for getting/creating an instance of a derived type with
/// parametric storage.
auto StorageUniquer::getParametricStorageTypeImpl(
TypeID id, unsigned hashValue,
function_ref<bool(const BaseStorage *)> isEqual,
function_ref<BaseStorage *(StorageAllocator &)> ctorFn) -> BaseStorage * {
return impl->getOrCreate(id, hashValue, isEqual, ctorFn);
}
/// Implementation for registering an instance of a derived type with
/// parametric storage.
void StorageUniquer::registerParametricStorageTypeImpl(
TypeID id, function_ref<void(BaseStorage *)> destructorFn) {
impl->parametricUniquers.try_emplace(
id, std::make_unique<ParametricStorageUniquer>(destructorFn));
}
/// Implementation for getting an instance of a derived type with default
/// storage.
auto StorageUniquer::getSingletonImpl(TypeID id) -> BaseStorage * {
return impl->getSingleton(id);
}
/// Test is the storage singleton is initialized.
bool StorageUniquer::isSingletonStorageInitialized(TypeID id) {
return impl->hasSingleton(id);
}
/// Test is the parametric storage is initialized.
bool StorageUniquer::isParametricStorageInitialized(TypeID id) {
return impl->hasParametricStorage(id);
}
/// Implementation for registering an instance of a derived type with default
/// storage.
void StorageUniquer::registerSingletonImpl(
TypeID id, function_ref<BaseStorage *(StorageAllocator &)> ctorFn) {
assert(!impl->singletonInstances.count(id) &&
"storage class already registered");
impl->singletonInstances.try_emplace(id, ctorFn(impl->singletonAllocator));
}
/// Implementation for mutating an instance of a derived storage.
LogicalResult StorageUniquer::mutateImpl(
TypeID id, BaseStorage *storage,
function_ref<LogicalResult(StorageAllocator &)> mutationFn) {
return impl->mutate(id, storage, mutationFn);
}