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//===- Allocator.h - Simple memory allocation abstraction -------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
/// \file
/// This file defines the BumpPtrAllocator interface. BumpPtrAllocator conforms
/// to the LLVM "Allocator" concept and is similar to MallocAllocator, but
/// objects cannot be deallocated. Their lifetime is tied to the lifetime of the
/// allocator.
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Alignment.h"
#include "llvm/Support/AllocatorBase.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/MemAlloc.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <cstdlib>
#include <iterator>
#include <type_traits>
#include <utility>
namespace llvm {
namespace detail {
// We call out to an external function to actually print the message as the
// printing code uses Allocator.h in its implementation.
void printBumpPtrAllocatorStats(unsigned NumSlabs, size_t BytesAllocated,
size_t TotalMemory);
} // end namespace detail
/// Allocate memory in an ever growing pool, as if by bump-pointer.
/// This isn't strictly a bump-pointer allocator as it uses backing slabs of
/// memory rather than relying on a boundless contiguous heap. However, it has
/// bump-pointer semantics in that it is a monotonically growing pool of memory
/// where every allocation is found by merely allocating the next N bytes in
/// the slab, or the next N bytes in the next slab.
/// Note that this also has a threshold for forcing allocations above a certain
/// size into their own slab.
/// The BumpPtrAllocatorImpl template defaults to using a MallocAllocator
/// object, which wraps malloc, to allocate memory, but it can be changed to
/// use a custom allocator.
/// The GrowthDelay specifies after how many allocated slabs the allocator
/// increases the size of the slabs.
template <typename AllocatorT = MallocAllocator, size_t SlabSize = 4096,
size_t SizeThreshold = SlabSize, size_t GrowthDelay = 128>
class BumpPtrAllocatorImpl
: public AllocatorBase<BumpPtrAllocatorImpl<AllocatorT, SlabSize,
SizeThreshold, GrowthDelay>>,
private AllocatorT {
static_assert(SizeThreshold <= SlabSize,
"The SizeThreshold must be at most the SlabSize to ensure "
"that objects larger than a slab go into their own memory "
static_assert(GrowthDelay > 0,
"GrowthDelay must be at least 1 which already increases the"
"slab size after each allocated slab.");
BumpPtrAllocatorImpl() = default;
template <typename T>
BumpPtrAllocatorImpl(T &&Allocator)
: AllocatorT(std::forward<T &&>(Allocator)) {}
// Manually implement a move constructor as we must clear the old allocator's
// slabs as a matter of correctness.
BumpPtrAllocatorImpl(BumpPtrAllocatorImpl &&Old)
: AllocatorT(static_cast<AllocatorT &&>(Old)), CurPtr(Old.CurPtr),
End(Old.End), Slabs(std::move(Old.Slabs)),
BytesAllocated(Old.BytesAllocated), RedZoneSize(Old.RedZoneSize) {
Old.CurPtr = Old.End = nullptr;
Old.BytesAllocated = 0;
~BumpPtrAllocatorImpl() {
DeallocateSlabs(Slabs.begin(), Slabs.end());
BumpPtrAllocatorImpl &operator=(BumpPtrAllocatorImpl &&RHS) {
DeallocateSlabs(Slabs.begin(), Slabs.end());
CurPtr = RHS.CurPtr;
End = RHS.End;
BytesAllocated = RHS.BytesAllocated;
RedZoneSize = RHS.RedZoneSize;
Slabs = std::move(RHS.Slabs);
CustomSizedSlabs = std::move(RHS.CustomSizedSlabs);
AllocatorT::operator=(static_cast<AllocatorT &&>(RHS));
RHS.CurPtr = RHS.End = nullptr;
RHS.BytesAllocated = 0;
return *this;
/// Deallocate all but the current slab and reset the current pointer
/// to the beginning of it, freeing all memory allocated so far.
void Reset() {
// Deallocate all but the first slab, and deallocate all custom-sized slabs.
if (Slabs.empty())
// Reset the state.
BytesAllocated = 0;
CurPtr = (char *)Slabs.front();
End = CurPtr + SlabSize;
__asan_poison_memory_region(*Slabs.begin(), computeSlabSize(0));
DeallocateSlabs(std::next(Slabs.begin()), Slabs.end());
Slabs.erase(std::next(Slabs.begin()), Slabs.end());
/// Allocate space at the specified alignment.
Allocate(size_t Size, Align Alignment) {
// Keep track of how many bytes we've allocated.
BytesAllocated += Size;
size_t Adjustment = offsetToAlignedAddr(CurPtr, Alignment);
assert(Adjustment + Size >= Size && "Adjustment + Size must not overflow");
size_t SizeToAllocate = Size;
// Add trailing bytes as a "red zone" under ASan.
SizeToAllocate += RedZoneSize;
// Check if we have enough space.
if (Adjustment + SizeToAllocate <= size_t(End - CurPtr)) {
char *AlignedPtr = CurPtr + Adjustment;
CurPtr = AlignedPtr + SizeToAllocate;
// Update the allocation point of this memory block in MemorySanitizer.
// Without this, MemorySanitizer messages for values originated from here
// will point to the allocation of the entire slab.
__msan_allocated_memory(AlignedPtr, Size);
// Similarly, tell ASan about this space.
__asan_unpoison_memory_region(AlignedPtr, Size);
return AlignedPtr;
// If Size is really big, allocate a separate slab for it.
size_t PaddedSize = SizeToAllocate + Alignment.value() - 1;
if (PaddedSize > SizeThreshold) {
void *NewSlab =
AllocatorT::Allocate(PaddedSize, alignof(std::max_align_t));
// We own the new slab and don't want anyone reading anyting other than
// pieces returned from this method. So poison the whole slab.
__asan_poison_memory_region(NewSlab, PaddedSize);
CustomSizedSlabs.push_back(std::make_pair(NewSlab, PaddedSize));
uintptr_t AlignedAddr = alignAddr(NewSlab, Alignment);
assert(AlignedAddr + Size <= (uintptr_t)NewSlab + PaddedSize);
char *AlignedPtr = (char*)AlignedAddr;
__msan_allocated_memory(AlignedPtr, Size);
__asan_unpoison_memory_region(AlignedPtr, Size);
return AlignedPtr;
// Otherwise, start a new slab and try again.
uintptr_t AlignedAddr = alignAddr(CurPtr, Alignment);
assert(AlignedAddr + SizeToAllocate <= (uintptr_t)End &&
"Unable to allocate memory!");
char *AlignedPtr = (char*)AlignedAddr;
CurPtr = AlignedPtr + SizeToAllocate;
__msan_allocated_memory(AlignedPtr, Size);
__asan_unpoison_memory_region(AlignedPtr, Size);
return AlignedPtr;
Allocate(size_t Size, size_t Alignment) {
assert(Alignment > 0 && "0-byte alignment is not allowed. Use 1 instead.");
return Allocate(Size, Align(Alignment));
// Pull in base class overloads.
using AllocatorBase<BumpPtrAllocatorImpl>::Allocate;
// Bump pointer allocators are expected to never free their storage; and
// clients expect pointers to remain valid for non-dereferencing uses even
// after deallocation.
void Deallocate(const void *Ptr, size_t Size, size_t /*Alignment*/) {
__asan_poison_memory_region(Ptr, Size);
// Pull in base class overloads.
using AllocatorBase<BumpPtrAllocatorImpl>::Deallocate;
size_t GetNumSlabs() const { return Slabs.size() + CustomSizedSlabs.size(); }
/// \return An index uniquely and reproducibly identifying
/// an input pointer \p Ptr in the given allocator.
/// The returned value is negative iff the object is inside a custom-size
/// slab.
/// Returns an empty optional if the pointer is not found in the allocator.
llvm::Optional<int64_t> identifyObject(const void *Ptr) {
const char *P = static_cast<const char *>(Ptr);
int64_t InSlabIdx = 0;
for (size_t Idx = 0, E = Slabs.size(); Idx < E; Idx++) {
const char *S = static_cast<const char *>(Slabs[Idx]);
if (P >= S && P < S + computeSlabSize(Idx))
return InSlabIdx + static_cast<int64_t>(P - S);
InSlabIdx += static_cast<int64_t>(computeSlabSize(Idx));
// Use negative index to denote custom sized slabs.
int64_t InCustomSizedSlabIdx = -1;
for (size_t Idx = 0, E = CustomSizedSlabs.size(); Idx < E; Idx++) {
const char *S = static_cast<const char *>(CustomSizedSlabs[Idx].first);
size_t Size = CustomSizedSlabs[Idx].second;
if (P >= S && P < S + Size)
return InCustomSizedSlabIdx - static_cast<int64_t>(P - S);
InCustomSizedSlabIdx -= static_cast<int64_t>(Size);
return None;
/// A wrapper around identifyObject that additionally asserts that
/// the object is indeed within the allocator.
/// \return An index uniquely and reproducibly identifying
/// an input pointer \p Ptr in the given allocator.
int64_t identifyKnownObject(const void *Ptr) {
Optional<int64_t> Out = identifyObject(Ptr);
assert(Out && "Wrong allocator used");
return *Out;
/// A wrapper around identifyKnownObject. Accepts type information
/// about the object and produces a smaller identifier by relying on
/// the alignment information. Note that sub-classes may have different
/// alignment, so the most base class should be passed as template parameter
/// in order to obtain correct results. For that reason automatic template
/// parameter deduction is disabled.
/// \return An index uniquely and reproducibly identifying
/// an input pointer \p Ptr in the given allocator. This identifier is
/// different from the ones produced by identifyObject and
/// identifyAlignedObject.
template <typename T>
int64_t identifyKnownAlignedObject(const void *Ptr) {
int64_t Out = identifyKnownObject(Ptr);
assert(Out % alignof(T) == 0 && "Wrong alignment information");
return Out / alignof(T);
size_t getTotalMemory() const {
size_t TotalMemory = 0;
for (auto I = Slabs.begin(), E = Slabs.end(); I != E; ++I)
TotalMemory += computeSlabSize(std::distance(Slabs.begin(), I));
for (const auto &PtrAndSize : CustomSizedSlabs)
TotalMemory += PtrAndSize.second;
return TotalMemory;
size_t getBytesAllocated() const { return BytesAllocated; }
void setRedZoneSize(size_t NewSize) {
RedZoneSize = NewSize;
void PrintStats() const {
detail::printBumpPtrAllocatorStats(Slabs.size(), BytesAllocated,
/// The current pointer into the current slab.
/// This points to the next free byte in the slab.
char *CurPtr = nullptr;
/// The end of the current slab.
char *End = nullptr;
/// The slabs allocated so far.
SmallVector<void *, 4> Slabs;
/// Custom-sized slabs allocated for too-large allocation requests.
SmallVector<std::pair<void *, size_t>, 0> CustomSizedSlabs;
/// How many bytes we've allocated.
/// Used so that we can compute how much space was wasted.
size_t BytesAllocated = 0;
/// The number of bytes to put between allocations when running under
/// a sanitizer.
size_t RedZoneSize = 1;
static size_t computeSlabSize(unsigned SlabIdx) {
// Scale the actual allocated slab size based on the number of slabs
// allocated. Every GrowthDelay slabs allocated, we double
// the allocated size to reduce allocation frequency, but saturate at
// multiplying the slab size by 2^30.
return SlabSize *
((size_t)1 << std::min<size_t>(30, SlabIdx / GrowthDelay));
/// Allocate a new slab and move the bump pointers over into the new
/// slab, modifying CurPtr and End.
void StartNewSlab() {
size_t AllocatedSlabSize = computeSlabSize(Slabs.size());
void *NewSlab =
AllocatorT::Allocate(AllocatedSlabSize, alignof(std::max_align_t));
// We own the new slab and don't want anyone reading anything other than
// pieces returned from this method. So poison the whole slab.
__asan_poison_memory_region(NewSlab, AllocatedSlabSize);
CurPtr = (char *)(NewSlab);
End = ((char *)NewSlab) + AllocatedSlabSize;
/// Deallocate a sequence of slabs.
void DeallocateSlabs(SmallVectorImpl<void *>::iterator I,
SmallVectorImpl<void *>::iterator E) {
for (; I != E; ++I) {
size_t AllocatedSlabSize =
computeSlabSize(std::distance(Slabs.begin(), I));
AllocatorT::Deallocate(*I, AllocatedSlabSize, alignof(std::max_align_t));
/// Deallocate all memory for custom sized slabs.
void DeallocateCustomSizedSlabs() {
for (auto &PtrAndSize : CustomSizedSlabs) {
void *Ptr = PtrAndSize.first;
size_t Size = PtrAndSize.second;
AllocatorT::Deallocate(Ptr, Size, alignof(std::max_align_t));
template <typename T> friend class SpecificBumpPtrAllocator;
/// The standard BumpPtrAllocator which just uses the default template
/// parameters.
typedef BumpPtrAllocatorImpl<> BumpPtrAllocator;
/// A BumpPtrAllocator that allows only elements of a specific type to be
/// allocated.
/// This allows calling the destructor in DestroyAll() and when the allocator is
/// destroyed.
template <typename T> class SpecificBumpPtrAllocator {
BumpPtrAllocator Allocator;
SpecificBumpPtrAllocator() {
// Because SpecificBumpPtrAllocator walks the memory to call destructors,
// it can't have red zones between allocations.
SpecificBumpPtrAllocator(SpecificBumpPtrAllocator &&Old)
: Allocator(std::move(Old.Allocator)) {}
~SpecificBumpPtrAllocator() { DestroyAll(); }
SpecificBumpPtrAllocator &operator=(SpecificBumpPtrAllocator &&RHS) {
Allocator = std::move(RHS.Allocator);
return *this;
/// Call the destructor of each allocated object and deallocate all but the
/// current slab and reset the current pointer to the beginning of it, freeing
/// all memory allocated so far.
void DestroyAll() {
auto DestroyElements = [](char *Begin, char *End) {
assert(Begin == (char *)alignAddr(Begin, Align::Of<T>()));
for (char *Ptr = Begin; Ptr + sizeof(T) <= End; Ptr += sizeof(T))
reinterpret_cast<T *>(Ptr)->~T();
for (auto I = Allocator.Slabs.begin(), E = Allocator.Slabs.end(); I != E;
++I) {
size_t AllocatedSlabSize = BumpPtrAllocator::computeSlabSize(
std::distance(Allocator.Slabs.begin(), I));
char *Begin = (char *)alignAddr(*I, Align::Of<T>());
char *End = *I == Allocator.Slabs.back() ? Allocator.CurPtr
: (char *)*I + AllocatedSlabSize;
DestroyElements(Begin, End);
for (auto &PtrAndSize : Allocator.CustomSizedSlabs) {
void *Ptr = PtrAndSize.first;
size_t Size = PtrAndSize.second;
DestroyElements((char *)alignAddr(Ptr, Align::Of<T>()),
(char *)Ptr + Size);
/// Allocate space for an array of objects without constructing them.
T *Allocate(size_t num = 1) { return Allocator.Allocate<T>(num); }
} // end namespace llvm
template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold,
size_t GrowthDelay>
void *
operator new(size_t Size,
llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold,
GrowthDelay> &Allocator) {
return Allocator.Allocate(Size, std::min((size_t)llvm::NextPowerOf2(Size),
template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold,
size_t GrowthDelay>
void operator delete(void *,
llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize,
SizeThreshold, GrowthDelay> &) {