1 //===--- Allocator.h - Simple memory allocation abstraction -----*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
11 /// This file defines the MallocAllocator and BumpPtrAllocator interfaces. Both
12 /// of these conform to an LLVM "Allocator" concept which consists of an
13 /// Allocate method accepting a size and alignment, and a Deallocate accepting
14 /// a pointer and size. Further, the LLVM "Allocator" concept has overloads of
15 /// Allocate and Deallocate for setting size and alignment based on the final
16 /// type. These overloads are typically provided by a base class template \c
19 //===----------------------------------------------------------------------===//
21 #ifndef LLVM_SUPPORT_ALLOCATOR_H
22 #define LLVM_SUPPORT_ALLOCATOR_H
24 #include "llvm/ADT/SmallVector.h"
25 #include "llvm/Support/AlignOf.h"
26 #include "llvm/Support/DataTypes.h"
27 #include "llvm/Support/MathExtras.h"
28 #include "llvm/Support/Memory.h"
35 template <typename T> struct ReferenceAdder {
38 template <typename T> struct ReferenceAdder<T &> {
42 /// \brief CRTP base class providing obvious overloads for the core \c
43 /// Allocate() methods of LLVM-style allocators.
45 /// This base class both documents the full public interface exposed by all
46 /// LLVM-style allocators, and redirects all of the overloads to a single core
47 /// set of methods which the derived class must define.
48 template <typename DerivedT> class AllocatorBase {
50 /// \brief Allocate \a Size bytes of \a Alignment aligned memory. This method
51 /// must be implemented by \c DerivedT.
52 void *Allocate(size_t Size, size_t Alignment) {
54 static_assert(static_cast<void *(AllocatorBase::*)(size_t, size_t)>(
55 &AllocatorBase::Allocate) !=
56 static_cast<void *(DerivedT::*)(size_t, size_t)>(
58 "Class derives from AllocatorBase without implementing the "
59 "core Allocate(size_t, size_t) overload!");
61 return static_cast<DerivedT *>(this)->Allocate(Size, Alignment);
64 /// \brief Deallocate \a Ptr to \a Size bytes of memory allocated by this
66 void Deallocate(const void *Ptr) {
68 static_assert(static_cast<void (AllocatorBase::*)(const void *)>(
69 &AllocatorBase::Deallocate) !=
70 static_cast<void (DerivedT::*)(const void *)>(
71 &DerivedT::Deallocate),
72 "Class derives from AllocatorBase without implementing the "
73 "core Deallocate(void *) overload!");
75 return static_cast<DerivedT *>(this)->Deallocate(Ptr);
78 // The rest of these methods are helpers that redirect to one of the above
81 /// \brief Allocate space for one object without constructing it.
82 template <typename T> T *Allocate() {
83 return static_cast<T *>(Allocate(sizeof(T), AlignOf<T>::Alignment));
86 /// \brief Allocate space for an array of objects without constructing them.
87 template <typename T> T *Allocate(size_t Num) {
88 return static_cast<T *>(Allocate(Num * sizeof(T), AlignOf<T>::Alignment));
91 /// \brief Allocate space for an array of objects with the specified alignment
92 /// and without constructing them.
93 template <typename T> T *Allocate(size_t Num, size_t Alignment) {
94 // Round EltSize up to the specified alignment.
95 size_t EltSize = (sizeof(T) + Alignment - 1) & (-Alignment);
96 return static_cast<T *>(Allocate(Num * EltSize, Alignment));
99 /// \brief Deallocate space for one object without destroying it.
100 template <typename T>
101 typename std::enable_if<
102 std::is_same<typename std::remove_cv<T>::type, void>::value, void>::type
104 Deallocate(static_cast<const void *>(Ptr));
107 /// \brief Allocate space for an array of objects without constructing them.
108 template <typename T>
109 typename std::enable_if<
110 std::is_same<typename std::remove_cv<T>::type, void>::value, void>::type
111 Deallocate(T *Ptr, size_t /*Num*/) {
112 Deallocate(static_cast<const void *>(Ptr));
116 class MallocAllocator : public AllocatorBase<MallocAllocator> {
119 ~MallocAllocator() {}
123 void *Allocate(size_t Size, size_t /*Alignment*/) { return malloc(Size); }
125 // Pull in base class overloads.
126 using AllocatorBase<MallocAllocator>::Allocate;
128 void Deallocate(const void *Ptr) { free(const_cast<void *>(Ptr)); }
130 // Pull in base class overloads.
131 using AllocatorBase<MallocAllocator>::Deallocate;
133 void PrintStats() const {}
136 /// MallocSlabAllocator - The default slab allocator for the bump allocator
137 /// is an adapter class for MallocAllocator that just forwards the method
138 /// calls and translates the arguments.
139 class MallocSlabAllocator {
140 /// Allocator - The underlying allocator that we forward to.
142 MallocAllocator Allocator;
145 void *Allocate(size_t Size) { return Allocator.Allocate(Size, 0); }
146 void Deallocate(void *Slab, size_t Size) { Allocator.Deallocate(Slab); }
151 // We call out to an external function to actually print the message as the
152 // printing code uses Allocator.h in its implementation.
153 void printBumpPtrAllocatorStats(unsigned NumSlabs, size_t BytesAllocated,
155 } // End namespace detail.
157 /// \brief Allocate memory in an ever growing pool, as if by bump-pointer.
159 /// This isn't strictly a bump-pointer allocator as it uses backing slabs of
160 /// memory rather than relying on boundless contiguous heap. However, it has
161 /// bump-pointer semantics in that is a monotonically growing pool of memory
162 /// where every allocation is found by merely allocating the next N bytes in
163 /// the slab, or the next N bytes in the next slab.
165 /// Note that this also has a threshold for forcing allocations above a certain
166 /// size into their own slab.
168 /// The BumpPtrAllocatorImpl template defaults to using a MallocSlabAllocator
169 /// object, which wraps malloc, to allocate memory, but it can be changed to
170 /// use a custom allocator.
171 template <typename AllocatorT = MallocSlabAllocator, size_t SlabSize = 4096,
172 size_t SizeThreshold = SlabSize>
173 class BumpPtrAllocatorImpl
174 : public AllocatorBase<
175 BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold>> {
176 BumpPtrAllocatorImpl(const BumpPtrAllocatorImpl &) LLVM_DELETED_FUNCTION;
177 void operator=(const BumpPtrAllocatorImpl &) LLVM_DELETED_FUNCTION;
180 static_assert(SizeThreshold <= SlabSize,
181 "The SizeThreshold must be at most the SlabSize to ensure "
182 "that objects larger than a slab go into their own memory "
185 BumpPtrAllocatorImpl()
186 : CurPtr(nullptr), End(nullptr), BytesAllocated(0), Allocator() {}
187 template <typename T>
188 BumpPtrAllocatorImpl(T &&Allocator)
189 : CurPtr(nullptr), End(nullptr), BytesAllocated(0),
190 Allocator(std::forward<T &&>(Allocator)) {}
191 ~BumpPtrAllocatorImpl() {
192 DeallocateSlabs(Slabs.begin(), Slabs.end());
193 DeallocateCustomSizedSlabs();
196 /// \brief Deallocate all but the current slab and reset the current pointer
197 /// to the beginning of it, freeing all memory allocated so far.
204 CurPtr = (char *)Slabs.front();
205 End = CurPtr + SlabSize;
207 // Deallocate all but the first slab, and all custome sized slabs.
208 DeallocateSlabs(std::next(Slabs.begin()), Slabs.end());
209 Slabs.erase(std::next(Slabs.begin()), Slabs.end());
210 DeallocateCustomSizedSlabs();
211 CustomSizedSlabs.clear();
214 /// \brief Allocate space at the specified alignment.
215 void *Allocate(size_t Size, size_t Alignment) {
216 if (!CurPtr) // Start a new slab if we haven't allocated one already.
219 // Keep track of how many bytes we've allocated.
220 BytesAllocated += Size;
222 // 0-byte alignment means 1-byte alignment.
226 // Allocate the aligned space, going forwards from CurPtr.
227 char *Ptr = alignPtr(CurPtr, Alignment);
229 // Check if we can hold it.
230 if (Ptr + Size <= End) {
232 // Update the allocation point of this memory block in MemorySanitizer.
233 // Without this, MemorySanitizer messages for values originated from here
234 // will point to the allocation of the entire slab.
235 __msan_allocated_memory(Ptr, Size);
239 // If Size is really big, allocate a separate slab for it.
240 size_t PaddedSize = Size + Alignment - 1;
241 if (PaddedSize > SizeThreshold) {
242 void *NewSlab = Allocator.Allocate(PaddedSize);
243 CustomSizedSlabs.push_back(std::make_pair(NewSlab, PaddedSize));
245 Ptr = alignPtr((char *)NewSlab, Alignment);
246 assert((uintptr_t)Ptr + Size <= (uintptr_t)NewSlab + PaddedSize);
247 __msan_allocated_memory(Ptr, Size);
251 // Otherwise, start a new slab and try again.
253 Ptr = alignPtr(CurPtr, Alignment);
255 assert(CurPtr <= End && "Unable to allocate memory!");
256 __msan_allocated_memory(Ptr, Size);
260 // Pull in base class overloads.
261 using AllocatorBase<BumpPtrAllocatorImpl>::Allocate;
263 void Deallocate(const void * /*Ptr*/) {}
265 // Pull in base class overloads.
266 using AllocatorBase<BumpPtrAllocatorImpl>::Deallocate;
268 size_t GetNumSlabs() const { return Slabs.size() + CustomSizedSlabs.size(); }
270 size_t getTotalMemory() const {
271 size_t TotalMemory = 0;
272 for (auto I = Slabs.begin(), E = Slabs.end(); I != E; ++I)
273 TotalMemory += computeSlabSize(std::distance(Slabs.begin(), I));
274 for (auto &PtrAndSize : CustomSizedSlabs)
275 TotalMemory += PtrAndSize.second;
279 void PrintStats() const {
280 detail::printBumpPtrAllocatorStats(Slabs.size(), BytesAllocated,
285 /// \brief The current pointer into the current slab.
287 /// This points to the next free byte in the slab.
290 /// \brief The end of the current slab.
293 /// \brief The slabs allocated so far.
294 SmallVector<void *, 4> Slabs;
296 /// \brief Custom-sized slabs allocated for too-large allocation requests.
297 SmallVector<std::pair<void *, size_t>, 0> CustomSizedSlabs;
299 /// \brief How many bytes we've allocated.
301 /// Used so that we can compute how much space was wasted.
302 size_t BytesAllocated;
304 /// \brief The allocator instance we use to get slabs of memory.
305 AllocatorT Allocator;
307 static size_t computeSlabSize(unsigned SlabIdx) {
308 // Scale the actual allocated slab size based on the number of slabs
309 // allocated. Every 128 slabs allocated, we double the allocated size to
310 // reduce allocation frequency, but saturate at multiplying the slab size by
312 return SlabSize * ((size_t)1 << std::min<size_t>(30, SlabIdx / 128));
315 /// \brief Allocate a new slab and move the bump pointers over into the new
316 /// slab, modifying CurPtr and End.
317 void StartNewSlab() {
318 size_t AllocatedSlabSize = computeSlabSize(Slabs.size());
320 void *NewSlab = Allocator.Allocate(AllocatedSlabSize);
321 Slabs.push_back(NewSlab);
322 CurPtr = (char *)(NewSlab);
323 End = ((char *)NewSlab) + AllocatedSlabSize;
326 /// \brief Deallocate a sequence of slabs.
327 void DeallocateSlabs(SmallVectorImpl<void *>::iterator I,
328 SmallVectorImpl<void *>::iterator E) {
329 for (; I != E; ++I) {
330 size_t AllocatedSlabSize =
331 computeSlabSize(std::distance(Slabs.begin(), I));
333 // Poison the memory so stale pointers crash sooner. Note we must
334 // preserve the Size and NextPtr fields at the beginning.
335 sys::Memory::setRangeWritable(*I, AllocatedSlabSize);
336 memset(*I, 0xCD, AllocatedSlabSize);
338 Allocator.Deallocate(*I, AllocatedSlabSize);
342 /// \brief Deallocate all memory for custom sized slabs.
343 void DeallocateCustomSizedSlabs() {
344 for (auto &PtrAndSize : CustomSizedSlabs) {
345 void *Ptr = PtrAndSize.first;
346 size_t Size = PtrAndSize.second;
348 // Poison the memory so stale pointers crash sooner. Note we must
349 // preserve the Size and NextPtr fields at the beginning.
350 sys::Memory::setRangeWritable(Ptr, Size);
351 memset(Ptr, 0xCD, Size);
353 Allocator.Deallocate(Ptr, Size);
357 template <typename T> friend class SpecificBumpPtrAllocator;
360 /// \brief The standard BumpPtrAllocator which just uses the default template
362 typedef BumpPtrAllocatorImpl<> BumpPtrAllocator;
364 /// \brief A BumpPtrAllocator that allows only elements of a specific type to be
367 /// This allows calling the destructor in DestroyAll() and when the allocator is
369 template <typename T> class SpecificBumpPtrAllocator {
370 BumpPtrAllocator Allocator;
373 SpecificBumpPtrAllocator() : Allocator() {}
375 ~SpecificBumpPtrAllocator() { DestroyAll(); }
377 /// Call the destructor of each allocated object and deallocate all but the
378 /// current slab and reset the current pointer to the beginning of it, freeing
379 /// all memory allocated so far.
381 auto DestroyElements = [](char *Begin, char *End) {
382 assert(Begin == alignPtr(Begin, alignOf<T>()));
383 for (char *Ptr = Begin; Ptr + sizeof(T) <= End; Ptr += sizeof(T))
384 reinterpret_cast<T *>(Ptr)->~T();
387 for (auto I = Allocator.Slabs.begin(), E = Allocator.Slabs.end(); I != E;
389 size_t AllocatedSlabSize = BumpPtrAllocator::computeSlabSize(
390 std::distance(Allocator.Slabs.begin(), I));
391 char *Begin = alignPtr((char *)*I, alignOf<T>());
392 char *End = *I == Allocator.Slabs.back() ? Allocator.CurPtr
393 : (char *)*I + AllocatedSlabSize;
395 DestroyElements(Begin, End);
398 for (auto &PtrAndSize : Allocator.CustomSizedSlabs) {
399 void *Ptr = PtrAndSize.first;
400 size_t Size = PtrAndSize.second;
401 DestroyElements(alignPtr((char *)Ptr, alignOf<T>()), (char *)Ptr + Size);
407 /// \brief Allocate space for an array of objects without constructing them.
408 T *Allocate(size_t num = 1) { return Allocator.Allocate<T>(num); }
413 } // end namespace llvm
415 template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold>
416 void *operator new(size_t Size,
417 llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize,
418 SizeThreshold> &Allocator) {
428 return Allocator.Allocate(
429 Size, std::min((size_t)llvm::NextPowerOf2(Size), offsetof(S, x)));
432 template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold>
433 void operator delete(
434 void *, llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold> &) {
437 #endif // LLVM_SUPPORT_ALLOCATOR_H