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