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 Allocate space for one object without constructing it.
65 template <typename T> T *Allocate() {
66 return static_cast<T *>(Allocate(sizeof(T), AlignOf<T>::Alignment));
69 /// \brief Allocate space for an array of objects without constructing them.
70 template <typename T> T *Allocate(size_t Num) {
71 return static_cast<T *>(Allocate(Num * sizeof(T), AlignOf<T>::Alignment));
74 /// \brief Allocate space for an array of objects with the specified alignment
75 /// and without constructing them.
76 template <typename T> T *Allocate(size_t Num, size_t Alignment) {
77 // Round EltSize up to the specified alignment.
78 size_t EltSize = (sizeof(T) + Alignment - 1) & (-Alignment);
79 return static_cast<T *>(Allocate(Num * EltSize, Alignment));
83 class MallocAllocator : public AllocatorBase<MallocAllocator> {
90 void *Allocate(size_t Size, size_t /*Alignment*/) { return malloc(Size); }
92 // Pull in base class overloads.
93 using AllocatorBase<MallocAllocator>::Allocate;
95 void Deallocate(const void *Ptr) { free(const_cast<void *>(Ptr)); }
97 void PrintStats() const {}
100 /// MallocSlabAllocator - The default slab allocator for the bump allocator
101 /// is an adapter class for MallocAllocator that just forwards the method
102 /// calls and translates the arguments.
103 class MallocSlabAllocator {
104 /// Allocator - The underlying allocator that we forward to.
106 MallocAllocator Allocator;
109 void *Allocate(size_t Size) { return Allocator.Allocate(Size, 0); }
110 void Deallocate(void *Slab, size_t Size) { Allocator.Deallocate(Slab); }
115 // We call out to an external function to actually print the message as the
116 // printing code uses Allocator.h in its implementation.
117 void printBumpPtrAllocatorStats(unsigned NumSlabs, size_t BytesAllocated,
119 } // End namespace detail.
121 /// \brief Allocate memory in an ever growing pool, as if by bump-pointer.
123 /// This isn't strictly a bump-pointer allocator as it uses backing slabs of
124 /// memory rather than relying on boundless contiguous heap. However, it has
125 /// bump-pointer semantics in that is a monotonically growing pool of memory
126 /// where every allocation is found by merely allocating the next N bytes in
127 /// the slab, or the next N bytes in the next slab.
129 /// Note that this also has a threshold for forcing allocations above a certain
130 /// size into their own slab.
132 /// The BumpPtrAllocatorImpl template defaults to using a MallocSlabAllocator
133 /// object, which wraps malloc, to allocate memory, but it can be changed to
134 /// use a custom allocator.
135 template <typename AllocatorT = MallocSlabAllocator, size_t SlabSize = 4096,
136 size_t SizeThreshold = SlabSize>
137 class BumpPtrAllocatorImpl
138 : public AllocatorBase<
139 BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold>> {
140 BumpPtrAllocatorImpl(const BumpPtrAllocatorImpl &) LLVM_DELETED_FUNCTION;
141 void operator=(const BumpPtrAllocatorImpl &) LLVM_DELETED_FUNCTION;
144 static_assert(SizeThreshold <= SlabSize,
145 "The SizeThreshold must be at most the SlabSize to ensure "
146 "that objects larger than a slab go into their own memory "
149 BumpPtrAllocatorImpl()
150 : CurPtr(nullptr), End(nullptr), BytesAllocated(0), Allocator() {}
151 template <typename T>
152 BumpPtrAllocatorImpl(T &&Allocator)
153 : CurPtr(nullptr), End(nullptr), BytesAllocated(0),
154 Allocator(std::forward<T &&>(Allocator)) {}
155 ~BumpPtrAllocatorImpl() {
156 DeallocateSlabs(Slabs.begin(), Slabs.end());
157 DeallocateCustomSizedSlabs();
160 /// \brief Deallocate all but the current slab and reset the current pointer
161 /// to the beginning of it, freeing all memory allocated so far.
168 CurPtr = (char *)Slabs.front();
169 End = CurPtr + SlabSize;
171 // Deallocate all but the first slab, and all custome sized slabs.
172 DeallocateSlabs(std::next(Slabs.begin()), Slabs.end());
173 Slabs.erase(std::next(Slabs.begin()), Slabs.end());
174 DeallocateCustomSizedSlabs();
175 CustomSizedSlabs.clear();
178 /// \brief Allocate space at the specified alignment.
179 void *Allocate(size_t Size, size_t Alignment) {
180 if (!CurPtr) // Start a new slab if we haven't allocated one already.
183 // Keep track of how many bytes we've allocated.
184 BytesAllocated += Size;
186 // 0-byte alignment means 1-byte alignment.
190 // Allocate the aligned space, going forwards from CurPtr.
191 char *Ptr = alignPtr(CurPtr, Alignment);
193 // Check if we can hold it.
194 if (Ptr + Size <= End) {
196 // Update the allocation point of this memory block in MemorySanitizer.
197 // Without this, MemorySanitizer messages for values originated from here
198 // will point to the allocation of the entire slab.
199 __msan_allocated_memory(Ptr, Size);
203 // If Size is really big, allocate a separate slab for it.
204 size_t PaddedSize = Size + Alignment - 1;
205 if (PaddedSize > SizeThreshold) {
206 void *NewSlab = Allocator.Allocate(PaddedSize);
207 CustomSizedSlabs.push_back(std::make_pair(NewSlab, PaddedSize));
209 Ptr = alignPtr((char *)NewSlab, Alignment);
210 assert((uintptr_t)Ptr + Size <= (uintptr_t)NewSlab + PaddedSize);
211 __msan_allocated_memory(Ptr, Size);
215 // Otherwise, start a new slab and try again.
217 Ptr = alignPtr(CurPtr, Alignment);
219 assert(CurPtr <= End && "Unable to allocate memory!");
220 __msan_allocated_memory(Ptr, Size);
224 // Pull in base class overloads.
225 using AllocatorBase<BumpPtrAllocatorImpl>::Allocate;
227 void Deallocate(const void * /*Ptr*/) {}
229 size_t GetNumSlabs() const { return Slabs.size() + CustomSizedSlabs.size(); }
231 size_t getTotalMemory() const {
232 size_t TotalMemory = 0;
233 for (auto I = Slabs.begin(), E = Slabs.end(); I != E; ++I)
234 TotalMemory += computeSlabSize(std::distance(Slabs.begin(), I));
235 for (auto &PtrAndSize : CustomSizedSlabs)
236 TotalMemory += PtrAndSize.second;
240 void PrintStats() const {
241 detail::printBumpPtrAllocatorStats(Slabs.size(), BytesAllocated,
246 /// \brief The current pointer into the current slab.
248 /// This points to the next free byte in the slab.
251 /// \brief The end of the current slab.
254 /// \brief The slabs allocated so far.
255 SmallVector<void *, 4> Slabs;
257 /// \brief Custom-sized slabs allocated for too-large allocation requests.
258 SmallVector<std::pair<void *, size_t>, 0> CustomSizedSlabs;
260 /// \brief How many bytes we've allocated.
262 /// Used so that we can compute how much space was wasted.
263 size_t BytesAllocated;
265 /// \brief The allocator instance we use to get slabs of memory.
266 AllocatorT Allocator;
268 static size_t computeSlabSize(unsigned SlabIdx) {
269 // Scale the actual allocated slab size based on the number of slabs
270 // allocated. Every 128 slabs allocated, we double the allocated size to
271 // reduce allocation frequency, but saturate at multiplying the slab size by
273 return SlabSize * ((size_t)1 << std::min<size_t>(30, SlabIdx / 128));
276 /// \brief Allocate a new slab and move the bump pointers over into the new
277 /// slab, modifying CurPtr and End.
278 void StartNewSlab() {
279 size_t AllocatedSlabSize = computeSlabSize(Slabs.size());
281 void *NewSlab = Allocator.Allocate(AllocatedSlabSize);
282 Slabs.push_back(NewSlab);
283 CurPtr = (char *)(NewSlab);
284 End = ((char *)NewSlab) + AllocatedSlabSize;
287 /// \brief Deallocate a sequence of slabs.
288 void DeallocateSlabs(SmallVectorImpl<void *>::iterator I,
289 SmallVectorImpl<void *>::iterator E) {
290 for (; I != E; ++I) {
291 size_t AllocatedSlabSize =
292 computeSlabSize(std::distance(Slabs.begin(), I));
294 // Poison the memory so stale pointers crash sooner. Note we must
295 // preserve the Size and NextPtr fields at the beginning.
296 sys::Memory::setRangeWritable(*I, AllocatedSlabSize);
297 memset(*I, 0xCD, AllocatedSlabSize);
299 Allocator.Deallocate(*I, AllocatedSlabSize);
303 /// \brief Deallocate all memory for custom sized slabs.
304 void DeallocateCustomSizedSlabs() {
305 for (auto &PtrAndSize : CustomSizedSlabs) {
306 void *Ptr = PtrAndSize.first;
307 size_t Size = PtrAndSize.second;
309 // Poison the memory so stale pointers crash sooner. Note we must
310 // preserve the Size and NextPtr fields at the beginning.
311 sys::Memory::setRangeWritable(Ptr, Size);
312 memset(Ptr, 0xCD, Size);
314 Allocator.Deallocate(Ptr, Size);
318 template <typename T> friend class SpecificBumpPtrAllocator;
321 /// \brief The standard BumpPtrAllocator which just uses the default template
323 typedef BumpPtrAllocatorImpl<> BumpPtrAllocator;
325 /// \brief A BumpPtrAllocator that allows only elements of a specific type to be
328 /// This allows calling the destructor in DestroyAll() and when the allocator is
330 template <typename T> class SpecificBumpPtrAllocator {
331 BumpPtrAllocator Allocator;
334 SpecificBumpPtrAllocator() : Allocator() {}
336 ~SpecificBumpPtrAllocator() { DestroyAll(); }
338 /// Call the destructor of each allocated object and deallocate all but the
339 /// current slab and reset the current pointer to the beginning of it, freeing
340 /// all memory allocated so far.
342 auto DestroyElements = [](char *Begin, char *End) {
343 assert(Begin == alignPtr(Begin, alignOf<T>()));
344 for (char *Ptr = Begin; Ptr + sizeof(T) <= End; Ptr += sizeof(T))
345 reinterpret_cast<T *>(Ptr)->~T();
348 for (auto I = Allocator.Slabs.begin(), E = Allocator.Slabs.end(); I != E;
350 size_t AllocatedSlabSize = BumpPtrAllocator::computeSlabSize(
351 std::distance(Allocator.Slabs.begin(), I));
352 char *Begin = alignPtr((char *)*I, alignOf<T>());
353 char *End = *I == Allocator.Slabs.back() ? Allocator.CurPtr
354 : (char *)*I + AllocatedSlabSize;
356 DestroyElements(Begin, End);
359 for (auto &PtrAndSize : Allocator.CustomSizedSlabs) {
360 void *Ptr = PtrAndSize.first;
361 size_t Size = PtrAndSize.second;
362 DestroyElements(alignPtr((char *)Ptr, alignOf<T>()), (char *)Ptr + Size);
368 /// \brief Allocate space for an array of objects without constructing them.
369 T *Allocate(size_t num = 1) { return Allocator.Allocate<T>(num); }
374 } // end namespace llvm
376 template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold>
377 void *operator new(size_t Size,
378 llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize,
379 SizeThreshold> &Allocator) {
389 return Allocator.Allocate(
390 Size, std::min((size_t)llvm::NextPowerOf2(Size), offsetof(S, x)));
393 template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold>
394 void operator delete(
395 void *, llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold> &) {
398 #endif // LLVM_SUPPORT_ALLOCATOR_H