llvm/include/llvm/Support/Allocator.h - llvm-project - Git at Google

 //===- Allocator.h - Simple memory allocation abstraction -------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt 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.
 ///
 //===----------------------------------------------------------------------===//

 #ifndef LLVM_SUPPORT_ALLOCATOR_H
 #define LLVM_SUPPORT_ALLOCATOR_H

 #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 {
 public:
   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 "
                 "allocation.");
   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)),
         CustomSizedSlabs(std::move(Old.CustomSizedSlabs)),
         BytesAllocated(Old.BytesAllocated), RedZoneSize(Old.RedZoneSize) {
     Old.CurPtr = Old.End = nullptr;
     Old.BytesAllocated = 0;
     Old.Slabs.clear();
     Old.CustomSizedSlabs.clear();
   }

   ~BumpPtrAllocatorImpl() {
     DeallocateSlabs(Slabs.begin(), Slabs.end());
     DeallocateCustomSizedSlabs();
   }

   BumpPtrAllocatorImpl &operator=(BumpPtrAllocatorImpl &&RHS) {
     DeallocateSlabs(Slabs.begin(), Slabs.end());
     DeallocateCustomSizedSlabs();

     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;
     RHS.Slabs.clear();
     RHS.CustomSizedSlabs.clear();
     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.
     DeallocateCustomSizedSlabs();
     CustomSizedSlabs.clear();

     if (Slabs.empty())
       return;

     // 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.
   LLVM_ATTRIBUTE_RETURNS_NONNULL LLVM_ATTRIBUTE_RETURNS_NOALIAS void *
   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;
 #if LLVM_ADDRESS_SANITIZER_BUILD
     // Add trailing bytes as a "red zone" under ASan.
     SizeToAllocate += RedZoneSize;
 #endif

     // 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.
     StartNewSlab();
     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;
   }

   inline LLVM_ATTRIBUTE_RETURNS_NONNULL LLVM_ATTRIBUTE_RETURNS_NOALIAS void *
   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,
                                        getTotalMemory());
   }

 private:
   /// 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);

     Slabs.push_back(NewSlab);
     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;

 public:
   SpecificBumpPtrAllocator() {
     // Because SpecificBumpPtrAllocator walks the memory to call destructors,
     // it can't have red zones between allocations.
     Allocator.setRedZoneSize(0);
   }
   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);
     }

     Allocator.Reset();
   }

   /// 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),
                                            alignof(std::max_align_t)));
 }

 template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold,
           size_t GrowthDelay>
 void operator delete(void *,
                      llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize,
                                                 SizeThreshold, GrowthDelay> &) {
 }

 #endif // LLVM_SUPPORT_ALLOCATOR_H
	//===- Allocator.h - Simple memory allocation abstraction -------- C++ --===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt 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.
	///
	//===----------------------------------------------------------------------===//

	#ifndef LLVM_SUPPORT_ALLOCATOR_H
	#define LLVM_SUPPORT_ALLOCATOR_H

	#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 {
	public:
	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 "
	"allocation.");
	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)),
	CustomSizedSlabs(std::move(Old.CustomSizedSlabs)),
	BytesAllocated(Old.BytesAllocated), RedZoneSize(Old.RedZoneSize) {
	Old.CurPtr = Old.End = nullptr;
	Old.BytesAllocated = 0;
	Old.Slabs.clear();
	Old.CustomSizedSlabs.clear();
	}

	~BumpPtrAllocatorImpl() {
	DeallocateSlabs(Slabs.begin(), Slabs.end());
	DeallocateCustomSizedSlabs();
	}

	BumpPtrAllocatorImpl &operator=(BumpPtrAllocatorImpl &&RHS) {
	DeallocateSlabs(Slabs.begin(), Slabs.end());
	DeallocateCustomSizedSlabs();

	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;
	RHS.Slabs.clear();
	RHS.CustomSizedSlabs.clear();
	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.
	DeallocateCustomSizedSlabs();
	CustomSizedSlabs.clear();

	if (Slabs.empty())
	return;

	// 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.
	LLVM_ATTRIBUTE_RETURNS_NONNULL LLVM_ATTRIBUTE_RETURNS_NOALIAS void *
	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;
	#if LLVM_ADDRESS_SANITIZER_BUILD
	// Add trailing bytes as a "red zone" under ASan.
	SizeToAllocate += RedZoneSize;
	#endif

	// 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.
	StartNewSlab();
	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;
	}

	inline LLVM_ATTRIBUTE_RETURNS_NONNULL LLVM_ATTRIBUTE_RETURNS_NOALIAS void *
	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,
	getTotalMemory());
	}

	private:
	/// 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);

	Slabs.push_back(NewSlab);
	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;

	public:
	SpecificBumpPtrAllocator() {
	// Because SpecificBumpPtrAllocator walks the memory to call destructors,
	// it can't have red zones between allocations.
	Allocator.setRedZoneSize(0);
	}
	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);
	}

	Allocator.Reset();
	}

	/// 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),
	alignof(std::max_align_t)));
	}

	template <typename AllocatorT, size_t SlabSize, size_t SizeThreshold,
	size_t GrowthDelay>
	void operator delete(void *,
	llvm::BumpPtrAllocatorImpl<AllocatorT, SlabSize,
	SizeThreshold, GrowthDelay> &) {
	}

	#endif // LLVM_SUPPORT_ALLOCATOR_H