aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/libs/llvm14/include/llvm/ADT/FunctionExtras.h
blob: 4792a3f364d7baa3bb709fe85520edd20ac4e8ec (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
#pragma once

#ifdef __GNUC__
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-parameter"
#endif

//===- FunctionExtras.h - Function type erasure utilities -------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
/// \file
/// This file provides a collection of function (or more generally, callable)
/// type erasure utilities supplementing those provided by the standard library
/// in `<function>`.
///
/// It provides `unique_function`, which works like `std::function` but supports
/// move-only callable objects and const-qualification.
///
/// Future plans:
/// - Add a `function` that provides ref-qualified support, which doesn't work
///   with `std::function`.
/// - Provide support for specifying multiple signatures to type erase callable
///   objects with an overload set, such as those produced by generic lambdas.
/// - Expand to include a copyable utility that directly replaces std::function
///   but brings the above improvements.
///
/// Note that LLVM's utilities are greatly simplified by not supporting
/// allocators.
///
/// If the standard library ever begins to provide comparable facilities we can
/// consider switching to those.
///
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_FUNCTIONEXTRAS_H
#define LLVM_ADT_FUNCTIONEXTRAS_H

#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/PointerUnion.h"
#include "llvm/ADT/STLForwardCompat.h"
#include "llvm/Support/MemAlloc.h"
#include "llvm/Support/type_traits.h"
#include <cstring>
#include <memory>
#include <type_traits>

namespace llvm {

/// unique_function is a type-erasing functor similar to std::function.
///
/// It can hold move-only function objects, like lambdas capturing unique_ptrs.
/// Accordingly, it is movable but not copyable.
///
/// It supports const-qualification:
/// - unique_function<int() const> has a const operator().
///   It can only hold functions which themselves have a const operator().
/// - unique_function<int()> has a non-const operator().
///   It can hold functions with a non-const operator(), like mutable lambdas.
template <typename FunctionT> class unique_function;

namespace detail {

template <typename T>
using EnableIfTrivial =
    std::enable_if_t<llvm::is_trivially_move_constructible<T>::value &&
                     std::is_trivially_destructible<T>::value>;
template <typename CallableT, typename ThisT>
using EnableUnlessSameType =
    std::enable_if_t<!std::is_same<remove_cvref_t<CallableT>, ThisT>::value>;
template <typename CallableT, typename Ret, typename... Params>
using EnableIfCallable = std::enable_if_t<llvm::disjunction<
    std::is_void<Ret>,
    std::is_same<decltype(std::declval<CallableT>()(std::declval<Params>()...)),
                 Ret>,
    std::is_same<const decltype(std::declval<CallableT>()(
                     std::declval<Params>()...)),
                 Ret>,
    std::is_convertible<decltype(std::declval<CallableT>()(
                            std::declval<Params>()...)),
                        Ret>>::value>;

template <typename ReturnT, typename... ParamTs> class UniqueFunctionBase {
protected:
  static constexpr size_t InlineStorageSize = sizeof(void *) * 3;

  template <typename T, class = void>
  struct IsSizeLessThanThresholdT : std::false_type {};

  template <typename T>
  struct IsSizeLessThanThresholdT<
      T, std::enable_if_t<sizeof(T) <= 2 * sizeof(void *)>> : std::true_type {};

  // Provide a type function to map parameters that won't observe extra copies
  // or moves and which are small enough to likely pass in register to values
  // and all other types to l-value reference types. We use this to compute the
  // types used in our erased call utility to minimize copies and moves unless
  // doing so would force things unnecessarily into memory.
  //
  // The heuristic used is related to common ABI register passing conventions.
  // It doesn't have to be exact though, and in one way it is more strict
  // because we want to still be able to observe either moves *or* copies.
  template <typename T> struct AdjustedParamTBase {
    static_assert(!std::is_reference<T>::value,
                  "references should be handled by template specialization");
    using type = typename std::conditional<
        llvm::is_trivially_copy_constructible<T>::value &&
            llvm::is_trivially_move_constructible<T>::value &&
            IsSizeLessThanThresholdT<T>::value,
        T, T &>::type;
  };

  // This specialization ensures that 'AdjustedParam<V<T>&>' or
  // 'AdjustedParam<V<T>&&>' does not trigger a compile-time error when 'T' is
  // an incomplete type and V a templated type.
  template <typename T> struct AdjustedParamTBase<T &> { using type = T &; };
  template <typename T> struct AdjustedParamTBase<T &&> { using type = T &; };

  template <typename T>
  using AdjustedParamT = typename AdjustedParamTBase<T>::type;

  // The type of the erased function pointer we use as a callback to dispatch to
  // the stored callable when it is trivial to move and destroy.
  using CallPtrT = ReturnT (*)(void *CallableAddr,
                               AdjustedParamT<ParamTs>... Params);
  using MovePtrT = void (*)(void *LHSCallableAddr, void *RHSCallableAddr);
  using DestroyPtrT = void (*)(void *CallableAddr);

  /// A struct to hold a single trivial callback with sufficient alignment for
  /// our bitpacking.
  struct alignas(8) TrivialCallback {
    CallPtrT CallPtr;
  };

  /// A struct we use to aggregate three callbacks when we need full set of
  /// operations.
  struct alignas(8) NonTrivialCallbacks {
    CallPtrT CallPtr;
    MovePtrT MovePtr;
    DestroyPtrT DestroyPtr;
  };

  // Create a pointer union between either a pointer to a static trivial call
  // pointer in a struct or a pointer to a static struct of the call, move, and
  // destroy pointers.
  using CallbackPointerUnionT =
      PointerUnion<TrivialCallback *, NonTrivialCallbacks *>;

  // The main storage buffer. This will either have a pointer to out-of-line
  // storage or an inline buffer storing the callable.
  union StorageUnionT {
    // For out-of-line storage we keep a pointer to the underlying storage and
    // the size. This is enough to deallocate the memory.
    struct OutOfLineStorageT {
      void *StoragePtr;
      size_t Size;
      size_t Alignment;
    } OutOfLineStorage;
    static_assert(
        sizeof(OutOfLineStorageT) <= InlineStorageSize,
        "Should always use all of the out-of-line storage for inline storage!");

    // For in-line storage, we just provide an aligned character buffer. We
    // provide three pointers worth of storage here.
    // This is mutable as an inlined `const unique_function<void() const>` may
    // still modify its own mutable members.
    mutable
        typename std::aligned_storage<InlineStorageSize, alignof(void *)>::type
            InlineStorage;
  } StorageUnion;

  // A compressed pointer to either our dispatching callback or our table of
  // dispatching callbacks and the flag for whether the callable itself is
  // stored inline or not.
  PointerIntPair<CallbackPointerUnionT, 1, bool> CallbackAndInlineFlag;

  bool isInlineStorage() const { return CallbackAndInlineFlag.getInt(); }

  bool isTrivialCallback() const {
    return CallbackAndInlineFlag.getPointer().template is<TrivialCallback *>();
  }

  CallPtrT getTrivialCallback() const {
    return CallbackAndInlineFlag.getPointer().template get<TrivialCallback *>()->CallPtr;
  }

  NonTrivialCallbacks *getNonTrivialCallbacks() const {
    return CallbackAndInlineFlag.getPointer()
        .template get<NonTrivialCallbacks *>();
  }

  CallPtrT getCallPtr() const {
    return isTrivialCallback() ? getTrivialCallback()
                               : getNonTrivialCallbacks()->CallPtr;
  }

  // These three functions are only const in the narrow sense. They return
  // mutable pointers to function state.
  // This allows unique_function<T const>::operator() to be const, even if the
  // underlying functor may be internally mutable.
  //
  // const callers must ensure they're only used in const-correct ways.
  void *getCalleePtr() const {
    return isInlineStorage() ? getInlineStorage() : getOutOfLineStorage();
  }
  void *getInlineStorage() const { return &StorageUnion.InlineStorage; }
  void *getOutOfLineStorage() const {
    return StorageUnion.OutOfLineStorage.StoragePtr;
  }

  size_t getOutOfLineStorageSize() const {
    return StorageUnion.OutOfLineStorage.Size;
  }
  size_t getOutOfLineStorageAlignment() const {
    return StorageUnion.OutOfLineStorage.Alignment;
  }

  void setOutOfLineStorage(void *Ptr, size_t Size, size_t Alignment) {
    StorageUnion.OutOfLineStorage = {Ptr, Size, Alignment};
  }

  template <typename CalledAsT>
  static ReturnT CallImpl(void *CallableAddr,
                          AdjustedParamT<ParamTs>... Params) {
    auto &Func = *reinterpret_cast<CalledAsT *>(CallableAddr);
    return Func(std::forward<ParamTs>(Params)...);
  }

  template <typename CallableT>
  static void MoveImpl(void *LHSCallableAddr, void *RHSCallableAddr) noexcept {
    new (LHSCallableAddr)
        CallableT(std::move(*reinterpret_cast<CallableT *>(RHSCallableAddr)));
  }

  template <typename CallableT>
  static void DestroyImpl(void *CallableAddr) noexcept {
    reinterpret_cast<CallableT *>(CallableAddr)->~CallableT();
  }

  // The pointers to call/move/destroy functions are determined for each
  // callable type (and called-as type, which determines the overload chosen).
  // (definitions are out-of-line).

  // By default, we need an object that contains all the different
  // type erased behaviors needed. Create a static instance of the struct type
  // here and each instance will contain a pointer to it.
  // Wrap in a struct to avoid https://gcc.gnu.org/PR71954
  template <typename CallableT, typename CalledAs, typename Enable = void>
  struct CallbacksHolder {
    static NonTrivialCallbacks Callbacks;
  };
  // See if we can create a trivial callback. We need the callable to be
  // trivially moved and trivially destroyed so that we don't have to store
  // type erased callbacks for those operations.
  template <typename CallableT, typename CalledAs>
  struct CallbacksHolder<CallableT, CalledAs, EnableIfTrivial<CallableT>> {
    static TrivialCallback Callbacks;
  };

  // A simple tag type so the call-as type to be passed to the constructor.
  template <typename T> struct CalledAs {};

  // Essentially the "main" unique_function constructor, but subclasses
  // provide the qualified type to be used for the call.
  // (We always store a T, even if the call will use a pointer to const T).
  template <typename CallableT, typename CalledAsT>
  UniqueFunctionBase(CallableT Callable, CalledAs<CalledAsT>) {
    bool IsInlineStorage = true;
    void *CallableAddr = getInlineStorage();
    if (sizeof(CallableT) > InlineStorageSize ||
        alignof(CallableT) > alignof(decltype(StorageUnion.InlineStorage))) {
      IsInlineStorage = false;
      // Allocate out-of-line storage. FIXME: Use an explicit alignment
      // parameter in C++17 mode.
      auto Size = sizeof(CallableT);
      auto Alignment = alignof(CallableT);
      CallableAddr = allocate_buffer(Size, Alignment);
      setOutOfLineStorage(CallableAddr, Size, Alignment);
    }

    // Now move into the storage.
    new (CallableAddr) CallableT(std::move(Callable));
    CallbackAndInlineFlag.setPointerAndInt(
        &CallbacksHolder<CallableT, CalledAsT>::Callbacks, IsInlineStorage);
  }

  ~UniqueFunctionBase() {
    if (!CallbackAndInlineFlag.getPointer())
      return;

    // Cache this value so we don't re-check it after type-erased operations.
    bool IsInlineStorage = isInlineStorage();

    if (!isTrivialCallback())
      getNonTrivialCallbacks()->DestroyPtr(
          IsInlineStorage ? getInlineStorage() : getOutOfLineStorage());

    if (!IsInlineStorage)
      deallocate_buffer(getOutOfLineStorage(), getOutOfLineStorageSize(),
                        getOutOfLineStorageAlignment());
  }

  UniqueFunctionBase(UniqueFunctionBase &&RHS) noexcept {
    // Copy the callback and inline flag.
    CallbackAndInlineFlag = RHS.CallbackAndInlineFlag;

    // If the RHS is empty, just copying the above is sufficient.
    if (!RHS)
      return;

    if (!isInlineStorage()) {
      // The out-of-line case is easiest to move.
      StorageUnion.OutOfLineStorage = RHS.StorageUnion.OutOfLineStorage;
    } else if (isTrivialCallback()) {
      // Move is trivial, just memcpy the bytes across.
      memcpy(getInlineStorage(), RHS.getInlineStorage(), InlineStorageSize);
    } else {
      // Non-trivial move, so dispatch to a type-erased implementation.
      getNonTrivialCallbacks()->MovePtr(getInlineStorage(),
                                        RHS.getInlineStorage());
    }

    // Clear the old callback and inline flag to get back to as-if-null.
    RHS.CallbackAndInlineFlag = {};

#ifndef NDEBUG
    // In debug builds, we also scribble across the rest of the storage.
    memset(RHS.getInlineStorage(), 0xAD, InlineStorageSize);
#endif
  }

  UniqueFunctionBase &operator=(UniqueFunctionBase &&RHS) noexcept {
    if (this == &RHS)
      return *this;

    // Because we don't try to provide any exception safety guarantees we can
    // implement move assignment very simply by first destroying the current
    // object and then move-constructing over top of it.
    this->~UniqueFunctionBase();
    new (this) UniqueFunctionBase(std::move(RHS));
    return *this;
  }

  UniqueFunctionBase() = default;

public:
  explicit operator bool() const {
    return (bool)CallbackAndInlineFlag.getPointer();
  }
};

template <typename R, typename... P>
template <typename CallableT, typename CalledAsT, typename Enable>
typename UniqueFunctionBase<R, P...>::NonTrivialCallbacks UniqueFunctionBase<
    R, P...>::CallbacksHolder<CallableT, CalledAsT, Enable>::Callbacks = {
    &CallImpl<CalledAsT>, &MoveImpl<CallableT>, &DestroyImpl<CallableT>};

template <typename R, typename... P>
template <typename CallableT, typename CalledAsT>
typename UniqueFunctionBase<R, P...>::TrivialCallback
    UniqueFunctionBase<R, P...>::CallbacksHolder<
        CallableT, CalledAsT, EnableIfTrivial<CallableT>>::Callbacks{
        &CallImpl<CalledAsT>};

} // namespace detail

template <typename R, typename... P>
class unique_function<R(P...)> : public detail::UniqueFunctionBase<R, P...> {
  using Base = detail::UniqueFunctionBase<R, P...>;

public:
  unique_function() = default;
  unique_function(std::nullptr_t) {}
  unique_function(unique_function &&) = default;
  unique_function(const unique_function &) = delete;
  unique_function &operator=(unique_function &&) = default;
  unique_function &operator=(const unique_function &) = delete;

  template <typename CallableT>
  unique_function(
      CallableT Callable,
      detail::EnableUnlessSameType<CallableT, unique_function> * = nullptr,
      detail::EnableIfCallable<CallableT, R, P...> * = nullptr)
      : Base(std::forward<CallableT>(Callable),
             typename Base::template CalledAs<CallableT>{}) {}

  R operator()(P... Params) {
    return this->getCallPtr()(this->getCalleePtr(), Params...);
  }
};

template <typename R, typename... P>
class unique_function<R(P...) const>
    : public detail::UniqueFunctionBase<R, P...> {
  using Base = detail::UniqueFunctionBase<R, P...>;

public:
  unique_function() = default;
  unique_function(std::nullptr_t) {}
  unique_function(unique_function &&) = default;
  unique_function(const unique_function &) = delete;
  unique_function &operator=(unique_function &&) = default;
  unique_function &operator=(const unique_function &) = delete;

  template <typename CallableT>
  unique_function(
      CallableT Callable,
      detail::EnableUnlessSameType<CallableT, unique_function> * = nullptr,
      detail::EnableIfCallable<const CallableT, R, P...> * = nullptr)
      : Base(std::forward<CallableT>(Callable),
             typename Base::template CalledAs<const CallableT>{}) {}

  R operator()(P... Params) const {
    return this->getCallPtr()(this->getCalleePtr(), Params...);
  }
};

} // end namespace llvm

#endif // LLVM_ADT_FUNCTIONEXTRAS_H

#ifdef __GNUC__
#pragma GCC diagnostic pop
#endif