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, size_t Size) {
68 static_assert(static_cast<void (AllocatorBase::*)(const void *, size_t)>(
69 &AllocatorBase::Deallocate) !=
70 static_cast<void (DerivedT::*)(const void *, size_t)>(
71 &DerivedT::Deallocate),
72 "Class derives from AllocatorBase without implementing the "
73 "core Deallocate(void *) overload!");
75 return static_cast<DerivedT *>(this)->Deallocate(Ptr, Size);
78 // The rest of these methods are helpers that redirect to one of the above
81 /// \brief Allocate space for a sequence of objects without constructing them.
82 template <typename T> T *Allocate(size_t Num = 1) {
83 return static_cast<T *>(Allocate(Num * sizeof(T), AlignOf<T>::Alignment));
86 /// \brief Deallocate space for a sequence of objects without constructing them.
88 typename std::enable_if<
89 !std::is_same<typename std::remove_cv<T>::type, void>::value, void>::type
90 Deallocate(T *Ptr, size_t Num = 1) {
91 Deallocate(static_cast<const void *>(Ptr), Num * sizeof(T));
95 class MallocAllocator : public AllocatorBase<MallocAllocator> {
102 void *Allocate(size_t Size, size_t /*Alignment*/) { return malloc(Size); }
104 // Pull in base class overloads.
105 using AllocatorBase<MallocAllocator>::Allocate;
107 void Deallocate(const void *Ptr, size_t /*Size*/) {
108 free(const_cast<void *>(Ptr));
111 // Pull in base class overloads.
112 using AllocatorBase<MallocAllocator>::Deallocate;
114 void PrintStats() const {}
119 // We call out to an external function to actually print the message as the
120 // printing code uses Allocator.h in its implementation.
121 void printBumpPtrAllocatorStats(unsigned NumSlabs, size_t BytesAllocated,
123 } // End namespace detail.
125 /// \brief Allocate memory in an ever growing pool, as if by bump-pointer.
127 /// This isn't strictly a bump-pointer allocator as it uses backing slabs of
128 /// memory rather than relying on boundless contiguous heap. However, it has
129 /// bump-pointer semantics in that is a monotonically growing pool of memory
130 /// where every allocation is found by merely allocating the next N bytes in
131 /// the slab, or the next N bytes in the next slab.
133 /// Note that this also has a threshold for forcing allocations above a certain
134 /// size into their own slab.
136 /// The BumpPtrAllocatorImpl template defaults to using a MallocAllocator
137 /// object, which wraps malloc, to allocate memory, but it can be changed to
138 /// use a custom allocator.
139 template <typename AllocatorT = MallocAllocator, size_t SlabSize = 4096,
140 size_t SizeThreshold = SlabSize>
141 class BumpPtrAllocatorImpl
142 : public AllocatorBase<
143 BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold>> {
144 BumpPtrAllocatorImpl(const BumpPtrAllocatorImpl &) LLVM_DELETED_FUNCTION;
145 void operator=(const BumpPtrAllocatorImpl &) LLVM_DELETED_FUNCTION;
148 static_assert(SizeThreshold <= SlabSize,
149 "The SizeThreshold must be at most the SlabSize to ensure "
150 "that objects larger than a slab go into their own memory "
153 BumpPtrAllocatorImpl()
154 : CurPtr(nullptr), End(nullptr), BytesAllocated(0), Allocator() {}
155 template <typename T>
156 BumpPtrAllocatorImpl(T &&Allocator)
157 : CurPtr(nullptr), End(nullptr), BytesAllocated(0),
158 Allocator(std::forward<T &&>(Allocator)) {}
159 ~BumpPtrAllocatorImpl() {
160 DeallocateSlabs(Slabs.begin(), Slabs.end());
161 DeallocateCustomSizedSlabs();
164 /// \brief Deallocate all but the current slab and reset the current pointer
165 /// to the beginning of it, freeing all memory allocated so far.
172 CurPtr = (char *)Slabs.front();
173 End = CurPtr + SlabSize;
175 // Deallocate all but the first slab, and all custome sized slabs.
176 DeallocateSlabs(std::next(Slabs.begin()), Slabs.end());
177 Slabs.erase(std::next(Slabs.begin()), Slabs.end());
178 DeallocateCustomSizedSlabs();
179 CustomSizedSlabs.clear();
182 /// \brief Allocate space at the specified alignment.
183 void *Allocate(size_t Size, size_t Alignment) {
184 if (!CurPtr) // Start a new slab if we haven't allocated one already.
187 // Keep track of how many bytes we've allocated.
188 BytesAllocated += Size;
190 // 0-byte alignment means 1-byte alignment.
194 // Allocate the aligned space, going forwards from CurPtr.
195 char *Ptr = alignPtr(CurPtr, Alignment);
197 // Check if we can hold it.
198 if (Ptr + Size <= End) {
200 // Update the allocation point of this memory block in MemorySanitizer.
201 // Without this, MemorySanitizer messages for values originated from here
202 // will point to the allocation of the entire slab.
203 __msan_allocated_memory(Ptr, Size);
207 // If Size is really big, allocate a separate slab for it.
208 size_t PaddedSize = Size + Alignment - 1;
209 if (PaddedSize > SizeThreshold) {
210 void *NewSlab = Allocator.Allocate(PaddedSize, 0);
211 CustomSizedSlabs.push_back(std::make_pair(NewSlab, PaddedSize));
213 Ptr = alignPtr((char *)NewSlab, Alignment);
214 assert((uintptr_t)Ptr + Size <= (uintptr_t)NewSlab + PaddedSize);
215 __msan_allocated_memory(Ptr, Size);
219 // Otherwise, start a new slab and try again.
221 Ptr = alignPtr(CurPtr, Alignment);
223 assert(CurPtr <= End && "Unable to allocate memory!");
224 __msan_allocated_memory(Ptr, Size);
228 // Pull in base class overloads.
229 using AllocatorBase<BumpPtrAllocatorImpl>::Allocate;
231 void Deallocate(const void * /*Ptr*/, size_t /*Size*/) {}
233 // Pull in base class overloads.
234 using AllocatorBase<BumpPtrAllocatorImpl>::Deallocate;
236 size_t GetNumSlabs() const { return Slabs.size() + CustomSizedSlabs.size(); }
238 size_t getTotalMemory() const {
239 size_t TotalMemory = 0;
240 for (auto I = Slabs.begin(), E = Slabs.end(); I != E; ++I)
241 TotalMemory += computeSlabSize(std::distance(Slabs.begin(), I));
242 for (auto &PtrAndSize : CustomSizedSlabs)
243 TotalMemory += PtrAndSize.second;
247 void PrintStats() const {
248 detail::printBumpPtrAllocatorStats(Slabs.size(), BytesAllocated,
253 /// \brief The current pointer into the current slab.
255 /// This points to the next free byte in the slab.
258 /// \brief The end of the current slab.
261 /// \brief The slabs allocated so far.
262 SmallVector<void *, 4> Slabs;
264 /// \brief Custom-sized slabs allocated for too-large allocation requests.
265 SmallVector<std::pair<void *, size_t>, 0> CustomSizedSlabs;
267 /// \brief How many bytes we've allocated.
269 /// Used so that we can compute how much space was wasted.
270 size_t BytesAllocated;
272 /// \brief The allocator instance we use to get slabs of memory.
273 AllocatorT Allocator;
275 static size_t computeSlabSize(unsigned SlabIdx) {
276 // Scale the actual allocated slab size based on the number of slabs
277 // allocated. Every 128 slabs allocated, we double the allocated size to
278 // reduce allocation frequency, but saturate at multiplying the slab size by
280 return SlabSize * ((size_t)1 << std::min<size_t>(30, SlabIdx / 128));
283 /// \brief Allocate a new slab and move the bump pointers over into the new
284 /// slab, modifying CurPtr and End.
285 void StartNewSlab() {
286 size_t AllocatedSlabSize = computeSlabSize(Slabs.size());
288 void *NewSlab = Allocator.Allocate(AllocatedSlabSize, 0);
289 Slabs.push_back(NewSlab);
290 CurPtr = (char *)(NewSlab);
291 End = ((char *)NewSlab) + AllocatedSlabSize;
294 /// \brief Deallocate a sequence of slabs.
295 void DeallocateSlabs(SmallVectorImpl<void *>::iterator I,
296 SmallVectorImpl<void *>::iterator E) {
297 for (; I != E; ++I) {
298 size_t AllocatedSlabSize =
299 computeSlabSize(std::distance(Slabs.begin(), I));
301 // Poison the memory so stale pointers crash sooner. Note we must
302 // preserve the Size and NextPtr fields at the beginning.
303 sys::Memory::setRangeWritable(*I, AllocatedSlabSize);
304 memset(*I, 0xCD, AllocatedSlabSize);
306 Allocator.Deallocate(*I, AllocatedSlabSize);
310 /// \brief Deallocate all memory for custom sized slabs.
311 void DeallocateCustomSizedSlabs() {
312 for (auto &PtrAndSize : CustomSizedSlabs) {
313 void *Ptr = PtrAndSize.first;
314 size_t Size = PtrAndSize.second;
316 // Poison the memory so stale pointers crash sooner. Note we must
317 // preserve the Size and NextPtr fields at the beginning.
318 sys::Memory::setRangeWritable(Ptr, Size);
319 memset(Ptr, 0xCD, Size);
321 Allocator.Deallocate(Ptr, Size);
325 template <typename T> friend class SpecificBumpPtrAllocator;
328 /// \brief The standard BumpPtrAllocator which just uses the default template
330 typedef BumpPtrAllocatorImpl<> BumpPtrAllocator;
332 /// \brief A BumpPtrAllocator that allows only elements of a specific type to be
335 /// This allows calling the destructor in DestroyAll() and when the allocator is
337 template <typename T> class SpecificBumpPtrAllocator {
338 BumpPtrAllocator Allocator;
341 SpecificBumpPtrAllocator() : Allocator() {}
343 ~SpecificBumpPtrAllocator() { DestroyAll(); }
345 /// Call the destructor of each allocated object and deallocate all but the
346 /// current slab and reset the current pointer to the beginning of it, freeing
347 /// all memory allocated so far.
349 auto DestroyElements = [](char *Begin, char *End) {
350 assert(Begin == alignPtr(Begin, alignOf<T>()));
351 for (char *Ptr = Begin; Ptr + sizeof(T) <= End; Ptr += sizeof(T))
352 reinterpret_cast<T *>(Ptr)->~T();
355 for (auto I = Allocator.Slabs.begin(), E = Allocator.Slabs.end(); I != E;
357 size_t AllocatedSlabSize = BumpPtrAllocator::computeSlabSize(
358 std::distance(Allocator.Slabs.begin(), I));
359 char *Begin = alignPtr((char *)*I, alignOf<T>());
360 char *End = *I == Allocator.Slabs.back() ? Allocator.CurPtr
361 : (char *)*I + AllocatedSlabSize;
363 DestroyElements(Begin, End);
366 for (auto &PtrAndSize : Allocator.CustomSizedSlabs) {
367 void *Ptr = PtrAndSize.first;
368 size_t Size = PtrAndSize.second;
369 DestroyElements(alignPtr((char *)Ptr, alignOf<T>()), (char *)Ptr + Size);
375 /// \brief Allocate space for an array of objects without constructing them.
376 T *Allocate(size_t num = 1) { return Allocator.Allocate<T>(num); }
381 } // end namespace llvm
383 template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold>
384 void *operator new(size_t Size,
385 llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize,
386 SizeThreshold> &Allocator) {
396 return Allocator.Allocate(
397 Size, std::min((size_t)llvm::NextPowerOf2(Size), offsetof(S, x)));
400 template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold>
401 void operator delete(
402 void *, llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold> &) {
405 #endif // LLVM_SUPPORT_ALLOCATOR_H