1//===- Allocator.h - Simple memory allocation abstraction -------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8/// \file
9///
10/// This file defines the BumpPtrAllocator interface. BumpPtrAllocator conforms
11/// to the LLVM "Allocator" concept and is similar to MallocAllocator, but
12/// objects cannot be deallocated. Their lifetime is tied to the lifetime of the
13/// allocator.
14///
15//===----------------------------------------------------------------------===//
16
17#ifndef LLVM_SUPPORT_ALLOCATOR_H
18#define LLVM_SUPPORT_ALLOCATOR_H
19
20#include "llvm/ADT/Optional.h"
21#include "llvm/ADT/SmallVector.h"
22#include "llvm/Support/Alignment.h"
23#include "llvm/Support/AllocatorBase.h"
24#include "llvm/Support/Compiler.h"
25#include "llvm/Support/ErrorHandling.h"
26#include "llvm/Support/MathExtras.h"
27#include "llvm/Support/MemAlloc.h"
28#include <algorithm>
29#include <cassert>
30#include <cstddef>
31#include <cstdint>
32#include <cstdlib>
33#include <iterator>
34#include <type_traits>
35#include <utility>
36
37namespace llvm {
38
39namespace detail {
40
41// We call out to an external function to actually print the message as the
42// printing code uses Allocator.h in its implementation.
43void printBumpPtrAllocatorStats(unsigned NumSlabs, size_t BytesAllocated,
44                                size_t TotalMemory);
45
46} // end namespace detail
47
48/// Allocate memory in an ever growing pool, as if by bump-pointer.
49///
50/// This isn't strictly a bump-pointer allocator as it uses backing slabs of
51/// memory rather than relying on a boundless contiguous heap. However, it has
52/// bump-pointer semantics in that it is a monotonically growing pool of memory
53/// where every allocation is found by merely allocating the next N bytes in
54/// the slab, or the next N bytes in the next slab.
55///
56/// Note that this also has a threshold for forcing allocations above a certain
57/// size into their own slab.
58///
59/// The BumpPtrAllocatorImpl template defaults to using a MallocAllocator
60/// object, which wraps malloc, to allocate memory, but it can be changed to
61/// use a custom allocator.
62///
63/// The GrowthDelay specifies after how many allocated slabs the allocator
64/// increases the size of the slabs.
65template <typename AllocatorT = MallocAllocator, size_t SlabSize = 4096,
66          size_t SizeThreshold = SlabSize, size_t GrowthDelay = 128>
67class BumpPtrAllocatorImpl
68    : public AllocatorBase<BumpPtrAllocatorImpl<AllocatorT, SlabSize,
69                                                SizeThreshold, GrowthDelay>> {
70public:
71  static_assert(SizeThreshold <= SlabSize,
72                "The SizeThreshold must be at most the SlabSize to ensure "
73                "that objects larger than a slab go into their own memory "
74                "allocation.");
75  static_assert(GrowthDelay > 0,
76                "GrowthDelay must be at least 1 which already increases the"
77                "slab size after each allocated slab.");
78
79  BumpPtrAllocatorImpl() = default;
80
81  template <typename T>
82  BumpPtrAllocatorImpl(T &&Allocator)
83      : Allocator(std::forward<T &&>(Allocator)) {}
84
85  // Manually implement a move constructor as we must clear the old allocator's
86  // slabs as a matter of correctness.
87  BumpPtrAllocatorImpl(BumpPtrAllocatorImpl &&Old)
88      : CurPtr(Old.CurPtr), End(Old.End), Slabs(std::move(Old.Slabs)),
89        CustomSizedSlabs(std::move(Old.CustomSizedSlabs)),
90        BytesAllocated(Old.BytesAllocated), RedZoneSize(Old.RedZoneSize),
91        Allocator(std::move(Old.Allocator)) {
92    Old.CurPtr = Old.End = nullptr;
93    Old.BytesAllocated = 0;
94    Old.Slabs.clear();
95    Old.CustomSizedSlabs.clear();
96  }
97
98  ~BumpPtrAllocatorImpl() {
99    DeallocateSlabs(Slabs.begin(), Slabs.end());
100    DeallocateCustomSizedSlabs();
101  }
102
103  BumpPtrAllocatorImpl &operator=(BumpPtrAllocatorImpl &&RHS) {
104    DeallocateSlabs(Slabs.begin(), Slabs.end());
105    DeallocateCustomSizedSlabs();
106
107    CurPtr = RHS.CurPtr;
108    End = RHS.End;
109    BytesAllocated = RHS.BytesAllocated;
110    RedZoneSize = RHS.RedZoneSize;
111    Slabs = std::move(RHS.Slabs);
112    CustomSizedSlabs = std::move(RHS.CustomSizedSlabs);
113    Allocator = std::move(RHS.Allocator);
114
115    RHS.CurPtr = RHS.End = nullptr;
116    RHS.BytesAllocated = 0;
117    RHS.Slabs.clear();
118    RHS.CustomSizedSlabs.clear();
119    return *this;
120  }
121
122  /// Deallocate all but the current slab and reset the current pointer
123  /// to the beginning of it, freeing all memory allocated so far.
124  void Reset() {
125    // Deallocate all but the first slab, and deallocate all custom-sized slabs.
126    DeallocateCustomSizedSlabs();
127    CustomSizedSlabs.clear();
128
129    if (Slabs.empty())
130      return;
131
132    // Reset the state.
133    BytesAllocated = 0;
134    CurPtr = (char *)Slabs.front();
135    End = CurPtr + SlabSize;
136
137    __asan_poison_memory_region(*Slabs.begin(), computeSlabSize(0));
138    DeallocateSlabs(std::next(Slabs.begin()), Slabs.end());
139    Slabs.erase(std::next(Slabs.begin()), Slabs.end());
140  }
141
142  /// Allocate space at the specified alignment.
143  LLVM_ATTRIBUTE_RETURNS_NONNULL LLVM_ATTRIBUTE_RETURNS_NOALIAS void *
144  Allocate(size_t Size, Align Alignment) {
145    // Keep track of how many bytes we've allocated.
146    BytesAllocated += Size;
147
148    size_t Adjustment = offsetToAlignedAddr(CurPtr, Alignment);
149    assert(Adjustment + Size >= Size && "Adjustment + Size must not overflow");
150
151    size_t SizeToAllocate = Size;
152#if LLVM_ADDRESS_SANITIZER_BUILD
153    // Add trailing bytes as a "red zone" under ASan.
154    SizeToAllocate += RedZoneSize;
155#endif
156
157    // Check if we have enough space.
158    if (Adjustment + SizeToAllocate <= size_t(End - CurPtr)) {
159      char *AlignedPtr = CurPtr + Adjustment;
160      CurPtr = AlignedPtr + SizeToAllocate;
161      // Update the allocation point of this memory block in MemorySanitizer.
162      // Without this, MemorySanitizer messages for values originated from here
163      // will point to the allocation of the entire slab.
164      __msan_allocated_memory(AlignedPtr, Size);
165      // Similarly, tell ASan about this space.
166      __asan_unpoison_memory_region(AlignedPtr, Size);
167      return AlignedPtr;
168    }
169
170    // If Size is really big, allocate a separate slab for it.
171    size_t PaddedSize = SizeToAllocate + Alignment.value() - 1;
172    if (PaddedSize > SizeThreshold) {
173      void *NewSlab = Allocator.Allocate(PaddedSize, alignof(std::max_align_t));
174      // We own the new slab and don't want anyone reading anyting other than
175      // pieces returned from this method.  So poison the whole slab.
176      __asan_poison_memory_region(NewSlab, PaddedSize);
177      CustomSizedSlabs.push_back(std::make_pair(NewSlab, PaddedSize));
178
179      uintptr_t AlignedAddr = alignAddr(NewSlab, Alignment);
180      assert(AlignedAddr + Size <= (uintptr_t)NewSlab + PaddedSize);
181      char *AlignedPtr = (char*)AlignedAddr;
182      __msan_allocated_memory(AlignedPtr, Size);
183      __asan_unpoison_memory_region(AlignedPtr, Size);
184      return AlignedPtr;
185    }
186
187    // Otherwise, start a new slab and try again.
188    StartNewSlab();
189    uintptr_t AlignedAddr = alignAddr(CurPtr, Alignment);
190    assert(AlignedAddr + SizeToAllocate <= (uintptr_t)End &&
191           "Unable to allocate memory!");
192    char *AlignedPtr = (char*)AlignedAddr;
193    CurPtr = AlignedPtr + SizeToAllocate;
194    __msan_allocated_memory(AlignedPtr, Size);
195    __asan_unpoison_memory_region(AlignedPtr, Size);
196    return AlignedPtr;
197  }
198
199  inline LLVM_ATTRIBUTE_RETURNS_NONNULL LLVM_ATTRIBUTE_RETURNS_NOALIAS void *
200  Allocate(size_t Size, size_t Alignment) {
201    assert(Alignment > 0 && "0-byte alignment is not allowed. Use 1 instead.");
202    return Allocate(Size, Align(Alignment));
203  }
204
205  // Pull in base class overloads.
206  using AllocatorBase<BumpPtrAllocatorImpl>::Allocate;
207
208  // Bump pointer allocators are expected to never free their storage; and
209  // clients expect pointers to remain valid for non-dereferencing uses even
210  // after deallocation.
211  void Deallocate(const void *Ptr, size_t Size, size_t /*Alignment*/) {
212    __asan_poison_memory_region(Ptr, Size);
213  }
214
215  // Pull in base class overloads.
216  using AllocatorBase<BumpPtrAllocatorImpl>::Deallocate;
217
218  size_t GetNumSlabs() const { return Slabs.size() + CustomSizedSlabs.size(); }
219
220  /// \return An index uniquely and reproducibly identifying
221  /// an input pointer \p Ptr in the given allocator.
222  /// The returned value is negative iff the object is inside a custom-size
223  /// slab.
224  /// Returns an empty optional if the pointer is not found in the allocator.
225  llvm::Optional<int64_t> identifyObject(const void *Ptr) {
226    const char *P = static_cast<const char *>(Ptr);
227    int64_t InSlabIdx = 0;
228    for (size_t Idx = 0, E = Slabs.size(); Idx < E; Idx++) {
229      const char *S = static_cast<const char *>(Slabs[Idx]);
230      if (P >= S && P < S + computeSlabSize(Idx))
231        return InSlabIdx + static_cast<int64_t>(P - S);
232      InSlabIdx += static_cast<int64_t>(computeSlabSize(Idx));
233    }
234
235    // Use negative index to denote custom sized slabs.
236    int64_t InCustomSizedSlabIdx = -1;
237    for (size_t Idx = 0, E = CustomSizedSlabs.size(); Idx < E; Idx++) {
238      const char *S = static_cast<const char *>(CustomSizedSlabs[Idx].first);
239      size_t Size = CustomSizedSlabs[Idx].second;
240      if (P >= S && P < S + Size)
241        return InCustomSizedSlabIdx - static_cast<int64_t>(P - S);
242      InCustomSizedSlabIdx -= static_cast<int64_t>(Size);
243    }
244    return None;
245  }
246
247  /// A wrapper around identifyObject that additionally asserts that
248  /// the object is indeed within the allocator.
249  /// \return An index uniquely and reproducibly identifying
250  /// an input pointer \p Ptr in the given allocator.
251  int64_t identifyKnownObject(const void *Ptr) {
252    Optional<int64_t> Out = identifyObject(Ptr);
253    assert(Out && "Wrong allocator used");
254    return *Out;
255  }
256
257  /// A wrapper around identifyKnownObject. Accepts type information
258  /// about the object and produces a smaller identifier by relying on
259  /// the alignment information. Note that sub-classes may have different
260  /// alignment, so the most base class should be passed as template parameter
261  /// in order to obtain correct results. For that reason automatic template
262  /// parameter deduction is disabled.
263  /// \return An index uniquely and reproducibly identifying
264  /// an input pointer \p Ptr in the given allocator. This identifier is
265  /// different from the ones produced by identifyObject and
266  /// identifyAlignedObject.
267  template <typename T>
268  int64_t identifyKnownAlignedObject(const void *Ptr) {
269    int64_t Out = identifyKnownObject(Ptr);
270    assert(Out % alignof(T) == 0 && "Wrong alignment information");
271    return Out / alignof(T);
272  }
273
274  size_t getTotalMemory() const {
275    size_t TotalMemory = 0;
276    for (auto I = Slabs.begin(), E = Slabs.end(); I != E; ++I)
277      TotalMemory += computeSlabSize(std::distance(Slabs.begin(), I));
278    for (auto &PtrAndSize : CustomSizedSlabs)
279      TotalMemory += PtrAndSize.second;
280    return TotalMemory;
281  }
282
283  size_t getBytesAllocated() const { return BytesAllocated; }
284
285  void setRedZoneSize(size_t NewSize) {
286    RedZoneSize = NewSize;
287  }
288
289  void PrintStats() const {
290    detail::printBumpPtrAllocatorStats(Slabs.size(), BytesAllocated,
291                                       getTotalMemory());
292  }
293
294private:
295  /// The current pointer into the current slab.
296  ///
297  /// This points to the next free byte in the slab.
298  char *CurPtr = nullptr;
299
300  /// The end of the current slab.
301  char *End = nullptr;
302
303  /// The slabs allocated so far.
304  SmallVector<void *, 4> Slabs;
305
306  /// Custom-sized slabs allocated for too-large allocation requests.
307  SmallVector<std::pair<void *, size_t>, 0> CustomSizedSlabs;
308
309  /// How many bytes we've allocated.
310  ///
311  /// Used so that we can compute how much space was wasted.
312  size_t BytesAllocated = 0;
313
314  /// The number of bytes to put between allocations when running under
315  /// a sanitizer.
316  size_t RedZoneSize = 1;
317
318  /// The allocator instance we use to get slabs of memory.
319  AllocatorT Allocator;
320
321  static size_t computeSlabSize(unsigned SlabIdx) {
322    // Scale the actual allocated slab size based on the number of slabs
323    // allocated. Every GrowthDelay slabs allocated, we double
324    // the allocated size to reduce allocation frequency, but saturate at
325    // multiplying the slab size by 2^30.
326    return SlabSize *
327           ((size_t)1 << std::min<size_t>(30, SlabIdx / GrowthDelay));
328  }
329
330  /// Allocate a new slab and move the bump pointers over into the new
331  /// slab, modifying CurPtr and End.
332  void StartNewSlab() {
333    size_t AllocatedSlabSize = computeSlabSize(Slabs.size());
334
335    void *NewSlab =
336        Allocator.Allocate(AllocatedSlabSize, alignof(std::max_align_t));
337    // We own the new slab and don't want anyone reading anything other than
338    // pieces returned from this method.  So poison the whole slab.
339    __asan_poison_memory_region(NewSlab, AllocatedSlabSize);
340
341    Slabs.push_back(NewSlab);
342    CurPtr = (char *)(NewSlab);
343    End = ((char *)NewSlab) + AllocatedSlabSize;
344  }
345
346  /// Deallocate a sequence of slabs.
347  void DeallocateSlabs(SmallVectorImpl<void *>::iterator I,
348                       SmallVectorImpl<void *>::iterator E) {
349    for (; I != E; ++I) {
350      size_t AllocatedSlabSize =
351          computeSlabSize(std::distance(Slabs.begin(), I));
352      Allocator.Deallocate(*I, AllocatedSlabSize, alignof(std::max_align_t));
353    }
354  }
355
356  /// Deallocate all memory for custom sized slabs.
357  void DeallocateCustomSizedSlabs() {
358    for (auto &PtrAndSize : CustomSizedSlabs) {
359      void *Ptr = PtrAndSize.first;
360      size_t Size = PtrAndSize.second;
361      Allocator.Deallocate(Ptr, Size, alignof(std::max_align_t));
362    }
363  }
364
365  template <typename T> friend class SpecificBumpPtrAllocator;
366};
367
368/// The standard BumpPtrAllocator which just uses the default template
369/// parameters.
370typedef BumpPtrAllocatorImpl<> BumpPtrAllocator;
371
372/// A BumpPtrAllocator that allows only elements of a specific type to be
373/// allocated.
374///
375/// This allows calling the destructor in DestroyAll() and when the allocator is
376/// destroyed.
377template <typename T> class SpecificBumpPtrAllocator {
378  BumpPtrAllocator Allocator;
379
380public:
381  SpecificBumpPtrAllocator() {
382    // Because SpecificBumpPtrAllocator walks the memory to call destructors,
383    // it can't have red zones between allocations.
384    Allocator.setRedZoneSize(0);
385  }
386  SpecificBumpPtrAllocator(SpecificBumpPtrAllocator &&Old)
387      : Allocator(std::move(Old.Allocator)) {}
388  ~SpecificBumpPtrAllocator() { DestroyAll(); }
389
390  SpecificBumpPtrAllocator &operator=(SpecificBumpPtrAllocator &&RHS) {
391    Allocator = std::move(RHS.Allocator);
392    return *this;
393  }
394
395  /// Call the destructor of each allocated object and deallocate all but the
396  /// current slab and reset the current pointer to the beginning of it, freeing
397  /// all memory allocated so far.
398  void DestroyAll() {
399    auto DestroyElements = [](char *Begin, char *End) {
400      assert(Begin == (char *)alignAddr(Begin, Align::Of<T>()));
401      for (char *Ptr = Begin; Ptr + sizeof(T) <= End; Ptr += sizeof(T))
402        reinterpret_cast<T *>(Ptr)->~T();
403    };
404
405    for (auto I = Allocator.Slabs.begin(), E = Allocator.Slabs.end(); I != E;
406         ++I) {
407      size_t AllocatedSlabSize = BumpPtrAllocator::computeSlabSize(
408          std::distance(Allocator.Slabs.begin(), I));
409      char *Begin = (char *)alignAddr(*I, Align::Of<T>());
410      char *End = *I == Allocator.Slabs.back() ? Allocator.CurPtr
411                                               : (char *)*I + AllocatedSlabSize;
412
413      DestroyElements(Begin, End);
414    }
415
416    for (auto &PtrAndSize : Allocator.CustomSizedSlabs) {
417      void *Ptr = PtrAndSize.first;
418      size_t Size = PtrAndSize.second;
419      DestroyElements((char *)alignAddr(Ptr, Align::Of<T>()),
420                      (char *)Ptr + Size);
421    }
422
423    Allocator.Reset();
424  }
425
426  /// Allocate space for an array of objects without constructing them.
427  T *Allocate(size_t num = 1) { return Allocator.Allocate<T>(num); }
428};
429
430} // end namespace llvm
431
432template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold,
433          size_t GrowthDelay>
434void *
435operator new(size_t Size,
436             llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold,
437                                        GrowthDelay> &Allocator) {
438  return Allocator.Allocate(Size, std::min((size_t)llvm::NextPowerOf2(Size),
439                                           alignof(std::max_align_t)));
440}
441
442template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold,
443          size_t GrowthDelay>
444void operator delete(void *,
445                     llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize,
446                                                SizeThreshold, GrowthDelay> &) {
447}
448
449#endif // LLVM_SUPPORT_ALLOCATOR_H
450