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) {
53 static_assert(static_cast<void *(AllocatorBase::*)(size_t, size_t)>(
54 &AllocatorBase::Allocate) !=
55 static_cast<void *(DerivedT::*)(size_t, size_t)>(
57 "Class derives from AllocatorBase without implementing the "
58 "core Allocate(size_t, size_t) overload!");
59 return static_cast<DerivedT *>(this)->Allocate(Size, Alignment);
62 /// \brief Allocate space for one object without constructing it.
63 template <typename T> T *Allocate() {
64 return static_cast<T *>(Allocate(sizeof(T), AlignOf<T>::Alignment));
67 /// \brief Allocate space for an array of objects without constructing them.
68 template <typename T> T *Allocate(size_t Num) {
69 return static_cast<T *>(Allocate(Num * sizeof(T), AlignOf<T>::Alignment));
72 /// \brief Allocate space for an array of objects with the specified alignment
73 /// and without constructing them.
74 template <typename T> T *Allocate(size_t Num, size_t Alignment) {
75 // Round EltSize up to the specified alignment.
76 size_t EltSize = (sizeof(T) + Alignment - 1) & (-Alignment);
77 return static_cast<T *>(Allocate(Num * EltSize, Alignment));
81 class MallocAllocator : public AllocatorBase<MallocAllocator> {
88 void *Allocate(size_t Size, size_t /*Alignment*/) { return malloc(Size); }
90 // Pull in base class overloads.
91 using AllocatorBase<MallocAllocator>::Allocate;
93 void Deallocate(const void *Ptr) { free(const_cast<void *>(Ptr)); }
95 void PrintStats() const {}
98 /// MallocSlabAllocator - The default slab allocator for the bump allocator
99 /// is an adapter class for MallocAllocator that just forwards the method
100 /// calls and translates the arguments.
101 class MallocSlabAllocator {
102 /// Allocator - The underlying allocator that we forward to.
104 MallocAllocator Allocator;
107 void *Allocate(size_t Size) { return Allocator.Allocate(Size, 0); }
108 void Deallocate(void *Slab, size_t Size) { Allocator.Deallocate(Slab); }
113 // We call out to an external function to actually print the message as the
114 // printing code uses Allocator.h in its implementation.
115 void printBumpPtrAllocatorStats(unsigned NumSlabs, size_t BytesAllocated,
117 } // End namespace detail.
119 /// \brief Allocate memory in an ever growing pool, as if by bump-pointer.
121 /// This isn't strictly a bump-pointer allocator as it uses backing slabs of
122 /// memory rather than relying on boundless contiguous heap. However, it has
123 /// bump-pointer semantics in that is a monotonically growing pool of memory
124 /// where every allocation is found by merely allocating the next N bytes in
125 /// the slab, or the next N bytes in the next slab.
127 /// Note that this also has a threshold for forcing allocations above a certain
128 /// size into their own slab.
130 /// The BumpPtrAllocatorImpl template defaults to using a MallocSlabAllocator
131 /// object, which wraps malloc, to allocate memory, but it can be changed to
132 /// use a custom allocator.
133 template <typename AllocatorT = MallocSlabAllocator, size_t SlabSize = 4096,
134 size_t SizeThreshold = SlabSize>
135 class BumpPtrAllocatorImpl
136 : public AllocatorBase<
137 BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold>> {
138 BumpPtrAllocatorImpl(const BumpPtrAllocatorImpl &) LLVM_DELETED_FUNCTION;
139 void operator=(const BumpPtrAllocatorImpl &) LLVM_DELETED_FUNCTION;
142 static_assert(SizeThreshold <= SlabSize,
143 "The SizeThreshold must be at most the SlabSize to ensure "
144 "that objects larger than a slab go into their own memory "
147 BumpPtrAllocatorImpl()
148 : CurPtr(nullptr), End(nullptr), BytesAllocated(0), Allocator() {}
149 template <typename T>
150 BumpPtrAllocatorImpl(T &&Allocator)
151 : CurPtr(nullptr), End(nullptr), BytesAllocated(0),
152 Allocator(std::forward<T &&>(Allocator)) {}
153 ~BumpPtrAllocatorImpl() {
154 DeallocateSlabs(Slabs.begin(), Slabs.end());
155 DeallocateCustomSizedSlabs();
158 /// \brief Deallocate all but the current slab and reset the current pointer
159 /// to the beginning of it, freeing all memory allocated so far.
166 CurPtr = (char *)Slabs.front();
167 End = CurPtr + SlabSize;
169 // Deallocate all but the first slab, and all custome sized slabs.
170 DeallocateSlabs(std::next(Slabs.begin()), Slabs.end());
171 Slabs.erase(std::next(Slabs.begin()), Slabs.end());
172 DeallocateCustomSizedSlabs();
173 CustomSizedSlabs.clear();
176 /// \brief Allocate space at the specified alignment.
177 void *Allocate(size_t Size, size_t Alignment) {
178 if (!CurPtr) // Start a new slab if we haven't allocated one already.
181 // Keep track of how many bytes we've allocated.
182 BytesAllocated += Size;
184 // 0-byte alignment means 1-byte alignment.
188 // Allocate the aligned space, going forwards from CurPtr.
189 char *Ptr = alignPtr(CurPtr, Alignment);
191 // Check if we can hold it.
192 if (Ptr + Size <= End) {
194 // Update the allocation point of this memory block in MemorySanitizer.
195 // Without this, MemorySanitizer messages for values originated from here
196 // will point to the allocation of the entire slab.
197 __msan_allocated_memory(Ptr, Size);
201 // If Size is really big, allocate a separate slab for it.
202 size_t PaddedSize = Size + Alignment - 1;
203 if (PaddedSize > SizeThreshold) {
204 void *NewSlab = Allocator.Allocate(PaddedSize);
205 CustomSizedSlabs.push_back(std::make_pair(NewSlab, PaddedSize));
207 Ptr = alignPtr((char *)NewSlab, Alignment);
208 assert((uintptr_t)Ptr + Size <= (uintptr_t)NewSlab + PaddedSize);
209 __msan_allocated_memory(Ptr, Size);
213 // Otherwise, start a new slab and try again.
215 Ptr = alignPtr(CurPtr, Alignment);
217 assert(CurPtr <= End && "Unable to allocate memory!");
218 __msan_allocated_memory(Ptr, Size);
222 // Pull in base class overloads.
223 using AllocatorBase<BumpPtrAllocatorImpl>::Allocate;
225 void Deallocate(const void * /*Ptr*/) {}
227 size_t GetNumSlabs() const { return Slabs.size() + CustomSizedSlabs.size(); }
229 size_t getTotalMemory() const {
230 size_t TotalMemory = 0;
231 for (auto I = Slabs.begin(), E = Slabs.end(); I != E; ++I)
232 TotalMemory += computeSlabSize(std::distance(Slabs.begin(), I));
233 for (auto &PtrAndSize : CustomSizedSlabs)
234 TotalMemory += PtrAndSize.second;
238 void PrintStats() const {
239 detail::printBumpPtrAllocatorStats(Slabs.size(), BytesAllocated,
244 /// \brief The current pointer into the current slab.
246 /// This points to the next free byte in the slab.
249 /// \brief The end of the current slab.
252 /// \brief The slabs allocated so far.
253 SmallVector<void *, 4> Slabs;
255 /// \brief Custom-sized slabs allocated for too-large allocation requests.
256 SmallVector<std::pair<void *, size_t>, 0> CustomSizedSlabs;
258 /// \brief How many bytes we've allocated.
260 /// Used so that we can compute how much space was wasted.
261 size_t BytesAllocated;
263 /// \brief The allocator instance we use to get slabs of memory.
264 AllocatorT Allocator;
266 static size_t computeSlabSize(unsigned SlabIdx) {
267 // Scale the actual allocated slab size based on the number of slabs
268 // allocated. Every 128 slabs allocated, we double the allocated size to
269 // reduce allocation frequency, but saturate at multiplying the slab size by
271 return SlabSize * ((size_t)1 << std::min<size_t>(30, SlabIdx / 128));
274 /// \brief Allocate a new slab and move the bump pointers over into the new
275 /// slab, modifying CurPtr and End.
276 void StartNewSlab() {
277 size_t AllocatedSlabSize = computeSlabSize(Slabs.size());
279 void *NewSlab = Allocator.Allocate(AllocatedSlabSize);
280 Slabs.push_back(NewSlab);
281 CurPtr = (char *)(NewSlab);
282 End = ((char *)NewSlab) + AllocatedSlabSize;
285 /// \brief Deallocate a sequence of slabs.
286 void DeallocateSlabs(SmallVectorImpl<void *>::iterator I,
287 SmallVectorImpl<void *>::iterator E) {
288 for (; I != E; ++I) {
289 size_t AllocatedSlabSize =
290 computeSlabSize(std::distance(Slabs.begin(), I));
292 // Poison the memory so stale pointers crash sooner. Note we must
293 // preserve the Size and NextPtr fields at the beginning.
294 sys::Memory::setRangeWritable(*I, AllocatedSlabSize);
295 memset(*I, 0xCD, AllocatedSlabSize);
297 Allocator.Deallocate(*I, AllocatedSlabSize);
301 /// \brief Deallocate all memory for custom sized slabs.
302 void DeallocateCustomSizedSlabs() {
303 for (auto &PtrAndSize : CustomSizedSlabs) {
304 void *Ptr = PtrAndSize.first;
305 size_t Size = PtrAndSize.second;
307 // Poison the memory so stale pointers crash sooner. Note we must
308 // preserve the Size and NextPtr fields at the beginning.
309 sys::Memory::setRangeWritable(Ptr, Size);
310 memset(Ptr, 0xCD, Size);
312 Allocator.Deallocate(Ptr, Size);
316 template <typename T> friend class SpecificBumpPtrAllocator;
319 /// \brief The standard BumpPtrAllocator which just uses the default template
321 typedef BumpPtrAllocatorImpl<> BumpPtrAllocator;
323 /// \brief A BumpPtrAllocator that allows only elements of a specific type to be
326 /// This allows calling the destructor in DestroyAll() and when the allocator is
328 template <typename T> class SpecificBumpPtrAllocator {
329 BumpPtrAllocator Allocator;
332 SpecificBumpPtrAllocator() : Allocator() {}
334 ~SpecificBumpPtrAllocator() { DestroyAll(); }
336 /// Call the destructor of each allocated object and deallocate all but the
337 /// current slab and reset the current pointer to the beginning of it, freeing
338 /// all memory allocated so far.
340 auto DestroyElements = [](char *Begin, char *End) {
341 assert(Begin == alignPtr(Begin, alignOf<T>()));
342 for (char *Ptr = Begin; Ptr + sizeof(T) <= End; Ptr += sizeof(T))
343 reinterpret_cast<T *>(Ptr)->~T();
346 for (auto I = Allocator.Slabs.begin(), E = Allocator.Slabs.end(); I != E;
348 size_t AllocatedSlabSize = BumpPtrAllocator::computeSlabSize(
349 std::distance(Allocator.Slabs.begin(), I));
350 char *Begin = alignPtr((char *)*I, alignOf<T>());
351 char *End = *I == Allocator.Slabs.back() ? Allocator.CurPtr
352 : (char *)*I + AllocatedSlabSize;
354 DestroyElements(Begin, End);
357 for (auto &PtrAndSize : Allocator.CustomSizedSlabs) {
358 void *Ptr = PtrAndSize.first;
359 size_t Size = PtrAndSize.second;
360 DestroyElements(alignPtr((char *)Ptr, alignOf<T>()), (char *)Ptr + Size);
366 /// \brief Allocate space for an array of objects without constructing them.
367 T *Allocate(size_t num = 1) { return Allocator.Allocate<T>(num); }
372 } // end namespace llvm
374 template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold>
375 void *operator new(size_t Size,
376 llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize,
377 SizeThreshold> &Allocator) {
387 return Allocator.Allocate(
388 Size, std::min((size_t)llvm::NextPowerOf2(Size), offsetof(S, x)));
391 template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold>
392 void operator delete(
393 void *, llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold> &) {
396 #endif // LLVM_SUPPORT_ALLOCATOR_H