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 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), sizeof(T));
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), Num * sizeof(T));
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, size_t /*Size*/) {
129 free(const_cast<void *>(Ptr));
132 // Pull in base class overloads.
133 using AllocatorBase<MallocAllocator>::Deallocate;
135 void PrintStats() const {}
140 // We call out to an external function to actually print the message as the
141 // printing code uses Allocator.h in its implementation.
142 void printBumpPtrAllocatorStats(unsigned NumSlabs, size_t BytesAllocated,
144 } // End namespace detail.
146 /// \brief Allocate memory in an ever growing pool, as if by bump-pointer.
148 /// This isn't strictly a bump-pointer allocator as it uses backing slabs of
149 /// memory rather than relying on boundless contiguous heap. However, it has
150 /// bump-pointer semantics in that is a monotonically growing pool of memory
151 /// where every allocation is found by merely allocating the next N bytes in
152 /// the slab, or the next N bytes in the next slab.
154 /// Note that this also has a threshold for forcing allocations above a certain
155 /// size into their own slab.
157 /// The BumpPtrAllocatorImpl template defaults to using a MallocAllocator
158 /// object, which wraps malloc, to allocate memory, but it can be changed to
159 /// use a custom allocator.
160 template <typename AllocatorT = MallocAllocator, size_t SlabSize = 4096,
161 size_t SizeThreshold = SlabSize>
162 class BumpPtrAllocatorImpl
163 : public AllocatorBase<
164 BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold>> {
165 BumpPtrAllocatorImpl(const BumpPtrAllocatorImpl &) LLVM_DELETED_FUNCTION;
166 void operator=(const BumpPtrAllocatorImpl &) LLVM_DELETED_FUNCTION;
169 static_assert(SizeThreshold <= SlabSize,
170 "The SizeThreshold must be at most the SlabSize to ensure "
171 "that objects larger than a slab go into their own memory "
174 BumpPtrAllocatorImpl()
175 : CurPtr(nullptr), End(nullptr), BytesAllocated(0), Allocator() {}
176 template <typename T>
177 BumpPtrAllocatorImpl(T &&Allocator)
178 : CurPtr(nullptr), End(nullptr), BytesAllocated(0),
179 Allocator(std::forward<T &&>(Allocator)) {}
180 ~BumpPtrAllocatorImpl() {
181 DeallocateSlabs(Slabs.begin(), Slabs.end());
182 DeallocateCustomSizedSlabs();
185 /// \brief Deallocate all but the current slab and reset the current pointer
186 /// to the beginning of it, freeing all memory allocated so far.
193 CurPtr = (char *)Slabs.front();
194 End = CurPtr + SlabSize;
196 // Deallocate all but the first slab, and all custome sized slabs.
197 DeallocateSlabs(std::next(Slabs.begin()), Slabs.end());
198 Slabs.erase(std::next(Slabs.begin()), Slabs.end());
199 DeallocateCustomSizedSlabs();
200 CustomSizedSlabs.clear();
203 /// \brief Allocate space at the specified alignment.
204 void *Allocate(size_t Size, size_t Alignment) {
205 if (!CurPtr) // Start a new slab if we haven't allocated one already.
208 // Keep track of how many bytes we've allocated.
209 BytesAllocated += Size;
211 // 0-byte alignment means 1-byte alignment.
215 // Allocate the aligned space, going forwards from CurPtr.
216 char *Ptr = alignPtr(CurPtr, Alignment);
218 // Check if we can hold it.
219 if (Ptr + Size <= End) {
221 // Update the allocation point of this memory block in MemorySanitizer.
222 // Without this, MemorySanitizer messages for values originated from here
223 // will point to the allocation of the entire slab.
224 __msan_allocated_memory(Ptr, Size);
228 // If Size is really big, allocate a separate slab for it.
229 size_t PaddedSize = Size + Alignment - 1;
230 if (PaddedSize > SizeThreshold) {
231 void *NewSlab = Allocator.Allocate(PaddedSize, 0);
232 CustomSizedSlabs.push_back(std::make_pair(NewSlab, PaddedSize));
234 Ptr = alignPtr((char *)NewSlab, Alignment);
235 assert((uintptr_t)Ptr + Size <= (uintptr_t)NewSlab + PaddedSize);
236 __msan_allocated_memory(Ptr, Size);
240 // Otherwise, start a new slab and try again.
242 Ptr = alignPtr(CurPtr, Alignment);
244 assert(CurPtr <= End && "Unable to allocate memory!");
245 __msan_allocated_memory(Ptr, Size);
249 // Pull in base class overloads.
250 using AllocatorBase<BumpPtrAllocatorImpl>::Allocate;
252 void Deallocate(const void * /*Ptr*/, size_t /*Size*/) {}
254 // Pull in base class overloads.
255 using AllocatorBase<BumpPtrAllocatorImpl>::Deallocate;
257 size_t GetNumSlabs() const { return Slabs.size() + CustomSizedSlabs.size(); }
259 size_t getTotalMemory() const {
260 size_t TotalMemory = 0;
261 for (auto I = Slabs.begin(), E = Slabs.end(); I != E; ++I)
262 TotalMemory += computeSlabSize(std::distance(Slabs.begin(), I));
263 for (auto &PtrAndSize : CustomSizedSlabs)
264 TotalMemory += PtrAndSize.second;
268 void PrintStats() const {
269 detail::printBumpPtrAllocatorStats(Slabs.size(), BytesAllocated,
274 /// \brief The current pointer into the current slab.
276 /// This points to the next free byte in the slab.
279 /// \brief The end of the current slab.
282 /// \brief The slabs allocated so far.
283 SmallVector<void *, 4> Slabs;
285 /// \brief Custom-sized slabs allocated for too-large allocation requests.
286 SmallVector<std::pair<void *, size_t>, 0> CustomSizedSlabs;
288 /// \brief How many bytes we've allocated.
290 /// Used so that we can compute how much space was wasted.
291 size_t BytesAllocated;
293 /// \brief The allocator instance we use to get slabs of memory.
294 AllocatorT Allocator;
296 static size_t computeSlabSize(unsigned SlabIdx) {
297 // Scale the actual allocated slab size based on the number of slabs
298 // allocated. Every 128 slabs allocated, we double the allocated size to
299 // reduce allocation frequency, but saturate at multiplying the slab size by
301 return SlabSize * ((size_t)1 << std::min<size_t>(30, SlabIdx / 128));
304 /// \brief Allocate a new slab and move the bump pointers over into the new
305 /// slab, modifying CurPtr and End.
306 void StartNewSlab() {
307 size_t AllocatedSlabSize = computeSlabSize(Slabs.size());
309 void *NewSlab = Allocator.Allocate(AllocatedSlabSize, 0);
310 Slabs.push_back(NewSlab);
311 CurPtr = (char *)(NewSlab);
312 End = ((char *)NewSlab) + AllocatedSlabSize;
315 /// \brief Deallocate a sequence of slabs.
316 void DeallocateSlabs(SmallVectorImpl<void *>::iterator I,
317 SmallVectorImpl<void *>::iterator E) {
318 for (; I != E; ++I) {
319 size_t AllocatedSlabSize =
320 computeSlabSize(std::distance(Slabs.begin(), I));
322 // Poison the memory so stale pointers crash sooner. Note we must
323 // preserve the Size and NextPtr fields at the beginning.
324 sys::Memory::setRangeWritable(*I, AllocatedSlabSize);
325 memset(*I, 0xCD, AllocatedSlabSize);
327 Allocator.Deallocate(*I, AllocatedSlabSize);
331 /// \brief Deallocate all memory for custom sized slabs.
332 void DeallocateCustomSizedSlabs() {
333 for (auto &PtrAndSize : CustomSizedSlabs) {
334 void *Ptr = PtrAndSize.first;
335 size_t Size = PtrAndSize.second;
337 // Poison the memory so stale pointers crash sooner. Note we must
338 // preserve the Size and NextPtr fields at the beginning.
339 sys::Memory::setRangeWritable(Ptr, Size);
340 memset(Ptr, 0xCD, Size);
342 Allocator.Deallocate(Ptr, Size);
346 template <typename T> friend class SpecificBumpPtrAllocator;
349 /// \brief The standard BumpPtrAllocator which just uses the default template
351 typedef BumpPtrAllocatorImpl<> BumpPtrAllocator;
353 /// \brief A BumpPtrAllocator that allows only elements of a specific type to be
356 /// This allows calling the destructor in DestroyAll() and when the allocator is
358 template <typename T> class SpecificBumpPtrAllocator {
359 BumpPtrAllocator Allocator;
362 SpecificBumpPtrAllocator() : Allocator() {}
364 ~SpecificBumpPtrAllocator() { DestroyAll(); }
366 /// Call the destructor of each allocated object and deallocate all but the
367 /// current slab and reset the current pointer to the beginning of it, freeing
368 /// all memory allocated so far.
370 auto DestroyElements = [](char *Begin, char *End) {
371 assert(Begin == alignPtr(Begin, alignOf<T>()));
372 for (char *Ptr = Begin; Ptr + sizeof(T) <= End; Ptr += sizeof(T))
373 reinterpret_cast<T *>(Ptr)->~T();
376 for (auto I = Allocator.Slabs.begin(), E = Allocator.Slabs.end(); I != E;
378 size_t AllocatedSlabSize = BumpPtrAllocator::computeSlabSize(
379 std::distance(Allocator.Slabs.begin(), I));
380 char *Begin = alignPtr((char *)*I, alignOf<T>());
381 char *End = *I == Allocator.Slabs.back() ? Allocator.CurPtr
382 : (char *)*I + AllocatedSlabSize;
384 DestroyElements(Begin, End);
387 for (auto &PtrAndSize : Allocator.CustomSizedSlabs) {
388 void *Ptr = PtrAndSize.first;
389 size_t Size = PtrAndSize.second;
390 DestroyElements(alignPtr((char *)Ptr, alignOf<T>()), (char *)Ptr + Size);
396 /// \brief Allocate space for an array of objects without constructing them.
397 T *Allocate(size_t num = 1) { return Allocator.Allocate<T>(num); }
402 } // end namespace llvm
404 template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold>
405 void *operator new(size_t Size,
406 llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize,
407 SizeThreshold> &Allocator) {
417 return Allocator.Allocate(
418 Size, std::min((size_t)llvm::NextPowerOf2(Size), offsetof(S, x)));
421 template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold>
422 void operator delete(
423 void *, llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold> &) {
426 #endif // LLVM_SUPPORT_ALLOCATOR_H