llvm/llvm/include/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/SmallVector.h"
#include "llvm/Support/Alignment.h"
#include "llvm/Support/AllocatorBase.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/MathExtras.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <optional>
#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 detail::AllocatorHolder<AllocatorT> { … };

/// The standard BumpPtrAllocator which just uses the default template
/// parameters.
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 { … };

} // 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) { … }

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