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//===--- Allocator.h - Simple memory allocation abstraction -----*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
/// \file
/// This file defines the MallocAllocator and BumpPtrAllocator interfaces. Both
/// of these conform to an LLVM "Allocator" concept which consists of an
/// Allocate method accepting a size and alignment, and a Deallocate accepting
/// a pointer and size. Further, the LLVM "Allocator" concept has overloads of
/// Allocate and Deallocate for setting size and alignment based on the final
/// type. These overloads are typically provided by a base class template \c
/// AllocatorBase.
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/AlignOf.h"
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/Memory.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdlib>
namespace llvm {
/// \brief CRTP base class providing obvious overloads for the core \c
/// Allocate() methods of LLVM-style allocators.
/// This base class both documents the full public interface exposed by all
/// LLVM-style allocators, and redirects all of the overloads to a single core
/// set of methods which the derived class must define.
template <typename DerivedT> class AllocatorBase {
/// \brief Allocate \a Size bytes of \a Alignment aligned memory. This method
/// must be implemented by \c DerivedT.
void *Allocate(size_t Size, size_t Alignment) {
#ifdef __clang__
static_assert(static_cast<void *(AllocatorBase::*)(size_t, size_t)>(
&AllocatorBase::Allocate) !=
static_cast<void *(DerivedT::*)(size_t, size_t)>(
"Class derives from AllocatorBase without implementing the "
"core Allocate(size_t, size_t) overload!");
return static_cast<DerivedT *>(this)->Allocate(Size, Alignment);
/// \brief Deallocate \a Ptr to \a Size bytes of memory allocated by this
/// allocator.
void Deallocate(const void *Ptr, size_t Size) {
#ifdef __clang__
static_assert(static_cast<void (AllocatorBase::*)(const void *, size_t)>(
&AllocatorBase::Deallocate) !=
static_cast<void (DerivedT::*)(const void *, size_t)>(
"Class derives from AllocatorBase without implementing the "
"core Deallocate(void *) overload!");
return static_cast<DerivedT *>(this)->Deallocate(Ptr, Size);
// The rest of these methods are helpers that redirect to one of the above
// core methods.
/// \brief Allocate space for a sequence of objects without constructing them.
template <typename T> T *Allocate(size_t Num = 1) {
return static_cast<T *>(Allocate(Num * sizeof(T), AlignOf<T>::Alignment));
/// \brief Deallocate space for a sequence of objects without constructing them.
template <typename T>
typename std::enable_if<
!std::is_same<typename std::remove_cv<T>::type, void>::value, void>::type
Deallocate(T *Ptr, size_t Num = 1) {
Deallocate(static_cast<const void *>(Ptr), Num * sizeof(T));
class MallocAllocator : public AllocatorBase<MallocAllocator> {
void Reset() {}
void *Allocate(size_t Size, size_t /*Alignment*/) { return malloc(Size); }
// Pull in base class overloads.
using AllocatorBase<MallocAllocator>::Allocate;
void Deallocate(const void *Ptr, size_t /*Size*/) {
free(const_cast<void *>(Ptr));
// Pull in base class overloads.
using AllocatorBase<MallocAllocator>::Deallocate;
void PrintStats() const {}
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.
/// \brief 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 boundless contiguous heap. However, it has
/// bump-pointer semantics in that 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.
template <typename AllocatorT = MallocAllocator, size_t SlabSize = 4096,
size_t SizeThreshold = SlabSize>
class BumpPtrAllocatorImpl
: public AllocatorBase<
BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold>> {
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 "
: CurPtr(nullptr), End(nullptr), BytesAllocated(0), Allocator() {}
template <typename T>
BumpPtrAllocatorImpl(T &&Allocator)
: CurPtr(nullptr), End(nullptr), BytesAllocated(0),
Allocator(std::forward<T &&>(Allocator)) {}
// Manually implement a move constructor as we must clear the old allocators
// slabs as a matter of correctness.
BumpPtrAllocatorImpl(BumpPtrAllocatorImpl &&Old)
: CurPtr(Old.CurPtr), End(Old.End), Slabs(std::move(Old.Slabs)),
Allocator(std::move(Old.Allocator)) {
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;
Slabs = std::move(RHS.Slabs);
CustomSizedSlabs = std::move(RHS.CustomSizedSlabs);
Allocator = std::move(RHS.Allocator);
RHS.CurPtr = RHS.End = nullptr;
RHS.BytesAllocated = 0;
return *this;
/// \brief Deallocate all but the current slab and reset the current pointer
/// to the beginning of it, freeing all memory allocated so far.
void Reset() {
if (Slabs.empty())
// Reset the state.
BytesAllocated = 0;
CurPtr = (char *)Slabs.front();
End = CurPtr + SlabSize;
// Deallocate all but the first slab, and all custome sized slabs.
DeallocateSlabs(std::next(Slabs.begin()), Slabs.end());
Slabs.erase(std::next(Slabs.begin()), Slabs.end());
/// \brief Allocate space at the specified alignment.
void *Allocate(size_t Size, size_t Alignment) {
if (!CurPtr) // Start a new slab if we haven't allocated one already.
// Keep track of how many bytes we've allocated.
BytesAllocated += Size;
// 0-byte alignment means 1-byte alignment.
if (Alignment == 0)
Alignment = 1;
// Allocate the aligned space, going forwards from CurPtr.
char *Ptr = alignPtr(CurPtr, Alignment);
// Check if we can hold it.
if (Ptr + Size <= End) {
CurPtr = Ptr + Size;
// 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(Ptr, Size);
return Ptr;
// If Size is really big, allocate a separate slab for it.
size_t PaddedSize = Size + Alignment - 1;
if (PaddedSize > SizeThreshold) {
void *NewSlab = Allocator.Allocate(PaddedSize, 0);
CustomSizedSlabs.push_back(std::make_pair(NewSlab, PaddedSize));
Ptr = alignPtr((char *)NewSlab, Alignment);
assert((uintptr_t)Ptr + Size <= (uintptr_t)NewSlab + PaddedSize);
__msan_allocated_memory(Ptr, Size);
return Ptr;
// Otherwise, start a new slab and try again.
Ptr = alignPtr(CurPtr, Alignment);
CurPtr = Ptr + Size;
assert(CurPtr <= End && "Unable to allocate memory!");
__msan_allocated_memory(Ptr, Size);
return Ptr;
// Pull in base class overloads.
using AllocatorBase<BumpPtrAllocatorImpl>::Allocate;
void Deallocate(const void * /*Ptr*/, size_t /*Size*/) {}
// Pull in base class overloads.
using AllocatorBase<BumpPtrAllocatorImpl>::Deallocate;
size_t GetNumSlabs() const { return Slabs.size() + CustomSizedSlabs.size(); }
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 (auto &PtrAndSize : CustomSizedSlabs)
TotalMemory += PtrAndSize.second;
return TotalMemory;
void PrintStats() const {
detail::printBumpPtrAllocatorStats(Slabs.size(), BytesAllocated,
/// \brief The current pointer into the current slab.
/// This points to the next free byte in the slab.
char *CurPtr;
/// \brief The end of the current slab.
char *End;
/// \brief The slabs allocated so far.
SmallVector<void *, 4> Slabs;
/// \brief Custom-sized slabs allocated for too-large allocation requests.
SmallVector<std::pair<void *, size_t>, 0> CustomSizedSlabs;
/// \brief How many bytes we've allocated.
/// Used so that we can compute how much space was wasted.
size_t BytesAllocated;
/// \brief The allocator instance we use to get slabs of memory.
AllocatorT Allocator;
static size_t computeSlabSize(unsigned SlabIdx) {
// Scale the actual allocated slab size based on the number of slabs
// allocated. Every 128 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 / 128));
/// \brief 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 = Allocator.Allocate(AllocatedSlabSize, 0);
CurPtr = (char *)(NewSlab);
End = ((char *)NewSlab) + AllocatedSlabSize;
/// \brief 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));
#ifndef NDEBUG
// Poison the memory so stale pointers crash sooner. Note we must
// preserve the Size and NextPtr fields at the beginning.
sys::Memory::setRangeWritable(*I, AllocatedSlabSize);
memset(*I, 0xCD, AllocatedSlabSize);
Allocator.Deallocate(*I, AllocatedSlabSize);
/// \brief Deallocate all memory for custom sized slabs.
void DeallocateCustomSizedSlabs() {
for (auto &PtrAndSize : CustomSizedSlabs) {
void *Ptr = PtrAndSize.first;
size_t Size = PtrAndSize.second;
#ifndef NDEBUG
// Poison the memory so stale pointers crash sooner. Note we must
// preserve the Size and NextPtr fields at the beginning.
sys::Memory::setRangeWritable(Ptr, Size);
memset(Ptr, 0xCD, Size);
Allocator.Deallocate(Ptr, Size);
template <typename T> friend class SpecificBumpPtrAllocator;
/// \brief The standard BumpPtrAllocator which just uses the default template
/// paramaters.
typedef BumpPtrAllocatorImpl<> BumpPtrAllocator;
/// \brief 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() : Allocator() {}
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 == alignPtr(Begin, alignOf<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 = alignPtr((char *)*I, alignOf<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(alignPtr((char *)Ptr, alignOf<T>()), (char *)Ptr + Size);
/// \brief 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>
void *operator new(size_t Size,
llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize,
SizeThreshold> &Allocator) {
struct S {
char c;
union {
double D;
long double LD;
long long L;
void *P;
} x;
return Allocator.Allocate(
Size, std::min((size_t)llvm::NextPowerOf2(Size), offsetof(S, x)));
template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold>
void operator delete(
void *, llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize, SizeThreshold> &) {