path: root/include/llvm/Support/Allocator.h

//===--- 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.
//
//===----------------------------------------------------------------------===//
//
// This file defines the MallocAllocator and BumpPtrAllocator interfaces.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_SUPPORT_ALLOCATOR_H
#define LLVM_SUPPORT_ALLOCATOR_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 {
template <typename T> struct ReferenceAdder {
  typedef T &result;
};
template <typename T> struct ReferenceAdder<T &> {
  typedef T result;
};

class MallocAllocator {
public:
  MallocAllocator() {}
  ~MallocAllocator() {}

  void Reset() {}

  void *Allocate(size_t Size, size_t /*Alignment*/) { return malloc(Size); }

  template <typename T> T *Allocate() {
    return static_cast<T *>(malloc(sizeof(T)));
  }

  template <typename T> T *Allocate(size_t Num) {
    return static_cast<T *>(malloc(sizeof(T) * Num));
  }

  void Deallocate(const void *Ptr) { free(const_cast<void *>(Ptr)); }

  void PrintStats() const {}
};

/// MemSlab - This structure lives at the beginning of every slab allocated by
/// the bump allocator.
class MemSlab {
public:
  size_t Size;
  MemSlab *NextPtr;
};

/// SlabAllocator - This class can be used to parameterize the underlying
/// allocation strategy for the bump allocator.  In particular, this is used
/// by the JIT to allocate contiguous swathes of executable memory.  The
/// interface uses MemSlab's instead of void *'s so that the allocator
/// doesn't have to remember the size of the pointer it allocated.
class SlabAllocator {
public:
  virtual ~SlabAllocator();
  virtual MemSlab *Allocate(size_t Size) = 0;
  virtual void Deallocate(MemSlab *Slab) = 0;
};

/// MallocSlabAllocator - The default slab allocator for the bump allocator
/// is an adapter class for MallocAllocator that just forwards the method
/// calls and translates the arguments.
class MallocSlabAllocator : public SlabAllocator {
  /// Allocator - The underlying allocator that we forward to.
  ///
  MallocAllocator Allocator;

public:
  MallocSlabAllocator() : Allocator() {}
  virtual ~MallocSlabAllocator();
  MemSlab *Allocate(size_t Size) override;
  void Deallocate(MemSlab *Slab) override;
};

/// \brief Non-templated base class for the \c BumpPtrAllocatorImpl template.
class BumpPtrAllocatorBase {
public:
  void Deallocate(const void * /*Ptr*/) {}
  void PrintStats() const;

  /// \brief Returns the total physical memory allocated by this allocator.
  size_t getTotalMemory() const;

protected:
  /// \brief The slab that we are currently allocating into.
  MemSlab *CurSlab;

  /// \brief How many bytes we've allocated.
  ///
  /// Used so that we can compute how much space was wasted.
  size_t BytesAllocated;

  BumpPtrAllocatorBase() : CurSlab(0), BytesAllocated(0) {}
};

/// \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.
template <size_t SlabSize = 4096, size_t SizeThreshold = SlabSize>
class BumpPtrAllocatorImpl : public BumpPtrAllocatorBase {
  BumpPtrAllocatorImpl(const BumpPtrAllocatorImpl &) LLVM_DELETED_FUNCTION;
  void operator=(const BumpPtrAllocatorImpl &) LLVM_DELETED_FUNCTION;

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.");

  BumpPtrAllocatorImpl()
      : Allocator(DefaultSlabAllocator), NumSlabs(0) {}
  BumpPtrAllocatorImpl(SlabAllocator &Allocator)
      : Allocator(Allocator), NumSlabs(0) {}
  ~BumpPtrAllocatorImpl() { DeallocateSlabs(CurSlab); }

  /// \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 (!CurSlab)
      return;
    DeallocateSlabs(CurSlab->NextPtr);
    CurSlab->NextPtr = 0;
    CurPtr = (char *)(CurSlab + 1);
    End = ((char *)CurSlab) + CurSlab->Size;
    BytesAllocated = 0;
  }

  /// \brief Allocate space at the specified alignment.
  void *Allocate(size_t Size, size_t Alignment) {
    if (!CurSlab) // Start a new slab if we haven't allocated one already.
      StartNewSlab();

    // 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 + sizeof(MemSlab) + Alignment - 1;
    if (PaddedSize > SizeThreshold) {
      ++NumSlabs;
      MemSlab *NewSlab = Allocator.Allocate(PaddedSize);

      // Put the new slab after the current slab, since we are not allocating
      // into it.
      NewSlab->NextPtr = CurSlab->NextPtr;
      CurSlab->NextPtr = NewSlab;

      Ptr = alignPtr((char *)(NewSlab + 1), Alignment);
      assert((uintptr_t)Ptr + Size <= (uintptr_t)NewSlab + NewSlab->Size);
      __msan_allocated_memory(Ptr, Size);
      return Ptr;
    }

    // Otherwise, start a new slab and try again.
    StartNewSlab();
    Ptr = alignPtr(CurPtr, Alignment);
    CurPtr = Ptr + Size;
    assert(CurPtr <= End && "Unable to allocate memory!");
    __msan_allocated_memory(Ptr, Size);
    return Ptr;
  }

  /// \brief Allocate space for one object without constructing it.
  template <typename T> T *Allocate() {
    return static_cast<T *>(Allocate(sizeof(T), AlignOf<T>::Alignment));
  }

  /// \brief Allocate space for an array of objects without constructing them.
  template <typename T> T *Allocate(size_t Num) {
    return static_cast<T *>(Allocate(Num * sizeof(T), AlignOf<T>::Alignment));
  }

  /// \brief Allocate space for an array of objects with the specified alignment
  /// and without constructing them.
  template <typename T> T *Allocate(size_t Num, size_t Alignment) {
    // Round EltSize up to the specified alignment.
    size_t EltSize = (sizeof(T) + Alignment - 1) & (-Alignment);
    return static_cast<T *>(Allocate(Num * EltSize, Alignment));
  }

  size_t GetNumSlabs() const { return NumSlabs; }

private:
  /// \brief The default allocator used if one is not provided.
  MallocSlabAllocator DefaultSlabAllocator;

  /// \brief The underlying allocator we use to get slabs of memory.
  ///
  /// This defaults to MallocSlabAllocator, which wraps malloc, but it could be
  /// changed to use a custom allocator.
  SlabAllocator &Allocator;

  /// \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 How many slabs we've allocated.
  ///
  /// Used to scale the size of each slab and reduce the number of allocations
  /// for extremely heavy memory use scenarios.
  size_t NumSlabs;

  /// \brief Allocate a new slab and move the bump pointers over into the new
  /// slab, modifying CurPtr and End.
  void StartNewSlab() {
    ++NumSlabs;
    // 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.
    // FIXME: Currently, this count includes special slabs for objects above the
    // size threshold. That will be fixed in a subsequent commit to make the
    // growth even more predictable.
    size_t AllocatedSlabSize =
        SlabSize * ((size_t)1 << std::min<size_t>(30, NumSlabs / 128));

    MemSlab *NewSlab = Allocator.Allocate(AllocatedSlabSize);
    NewSlab->NextPtr = CurSlab;
    CurSlab = NewSlab;
    CurPtr = (char *)(CurSlab + 1);
    End = ((char *)CurSlab) + CurSlab->Size;
  }

  /// \brief Deallocate all memory slabs after and including this one.
  void DeallocateSlabs(MemSlab *Slab) {
    while (Slab) {
      MemSlab *NextSlab = Slab->NextPtr;
#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(Slab + 1, Slab->Size - sizeof(MemSlab));
      memset(Slab + 1, 0xCD, Slab->Size - sizeof(MemSlab));
#endif
      Allocator.Deallocate(Slab);
      Slab = NextSlab;
      --NumSlabs;
    }
  }

  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;

public:
  SpecificBumpPtrAllocator() : Allocator() {}
  SpecificBumpPtrAllocator(SlabAllocator &allocator) : Allocator(allocator) {}

  ~SpecificBumpPtrAllocator() { DestroyAll(); }

  /// 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() {
    MemSlab *Slab = Allocator.CurSlab;
    while (Slab) {
      char *End = Slab == Allocator.CurSlab ? Allocator.CurPtr
                                            : (char *)Slab + Slab->Size;
      for (char *Ptr = (char *)(Slab + 1); Ptr < End; Ptr += sizeof(T)) {
        Ptr = alignPtr(Ptr, alignOf<T>());
        if (Ptr + sizeof(T) <= End)
          reinterpret_cast<T *>(Ptr)->~T();
      }
      Slab = Slab->NextPtr;
    }
    Allocator.Reset();
  }

  /// \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 <size_t SlabSize, size_t SizeThreshold>
void *
operator new(size_t Size,
             llvm::BumpPtrAllocatorImpl<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 <size_t SlabSize, size_t SizeThreshold>
void operator delete(void *,
                     llvm::BumpPtrAllocatorImpl<SlabSize, SizeThreshold> &) {}

#endif // LLVM_SUPPORT_ALLOCATOR_H