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//===--- Allocator.cpp - Simple memory allocation abstraction -------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the BumpPtrAllocator interface.
//
//===----------------------------------------------------------------------===//
#include "llvm/Support/Allocator.h"
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/Recycler.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/Memory.h"
#include <cstring>
namespace llvm {
BumpPtrAllocator::BumpPtrAllocator(size_t size, size_t threshold,
SlabAllocator &allocator)
: SlabSize(size), SizeThreshold(threshold), Allocator(allocator),
CurSlab(0), BytesAllocated(0) { }
BumpPtrAllocator::~BumpPtrAllocator() {
DeallocateSlabs(CurSlab);
}
/// AlignPtr - Align Ptr to Alignment bytes, rounding up. Alignment should
/// be a power of two. This method rounds up, so AlignPtr(7, 4) == 8 and
/// AlignPtr(8, 4) == 8.
char *BumpPtrAllocator::AlignPtr(char *Ptr, size_t Alignment) {
assert(Alignment && (Alignment & (Alignment - 1)) == 0 &&
"Alignment is not a power of two!");
// Do the alignment.
return (char*)(((uintptr_t)Ptr + Alignment - 1) &
~(uintptr_t)(Alignment - 1));
}
/// StartNewSlab - Allocate a new slab and move the bump pointers over into
/// the new slab. Modifies CurPtr and End.
void BumpPtrAllocator::StartNewSlab() {
// If we allocated a big number of slabs already it's likely that we're going
// to allocate more. Increase slab size to reduce mallocs and possibly memory
// overhead. The factors are chosen conservatively to avoid overallocation.
if (BytesAllocated >= SlabSize * 128)
SlabSize *= 2;
MemSlab *NewSlab = Allocator.Allocate(SlabSize);
NewSlab->NextPtr = CurSlab;
CurSlab = NewSlab;
CurPtr = (char*)(CurSlab + 1);
End = ((char*)CurSlab) + CurSlab->Size;
}
/// DeallocateSlabs - Deallocate all memory slabs after and including this
/// one.
void BumpPtrAllocator::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;
}
}
/// Reset - Deallocate all but the current slab and reset the current pointer
/// to the beginning of it, freeing all memory allocated so far.
void BumpPtrAllocator::Reset() {
if (!CurSlab)
return;
DeallocateSlabs(CurSlab->NextPtr);
CurSlab->NextPtr = 0;
CurPtr = (char*)(CurSlab + 1);
End = ((char*)CurSlab) + CurSlab->Size;
}
/// Allocate - Allocate space at the specified alignment.
///
void *BumpPtrAllocator::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;
return Ptr;
}
// If Size is really big, allocate a separate slab for it.
size_t PaddedSize = Size + sizeof(MemSlab) + Alignment - 1;
if (PaddedSize > SizeThreshold) {
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);
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!");
return Ptr;
}
unsigned BumpPtrAllocator::GetNumSlabs() const {
unsigned NumSlabs = 0;
for (MemSlab *Slab = CurSlab; Slab != 0; Slab = Slab->NextPtr) {
++NumSlabs;
}
return NumSlabs;
}
void BumpPtrAllocator::PrintStats() const {
unsigned NumSlabs = 0;
size_t TotalMemory = 0;
for (MemSlab *Slab = CurSlab; Slab != 0; Slab = Slab->NextPtr) {
TotalMemory += Slab->Size;
++NumSlabs;
}
errs() << "\nNumber of memory regions: " << NumSlabs << '\n'
<< "Bytes used: " << BytesAllocated << '\n'
<< "Bytes allocated: " << TotalMemory << '\n'
<< "Bytes wasted: " << (TotalMemory - BytesAllocated)
<< " (includes alignment, etc)\n";
}
MallocSlabAllocator BumpPtrAllocator::DefaultSlabAllocator =
MallocSlabAllocator();
SlabAllocator::~SlabAllocator() { }
MallocSlabAllocator::~MallocSlabAllocator() { }
MemSlab *MallocSlabAllocator::Allocate(size_t Size) {
MemSlab *Slab = (MemSlab*)Allocator.Allocate(Size, 0);
Slab->Size = Size;
Slab->NextPtr = 0;
return Slab;
}
void MallocSlabAllocator::Deallocate(MemSlab *Slab) {
Allocator.Deallocate(Slab);
}
void PrintRecyclerStats(size_t Size,
size_t Align,
size_t FreeListSize) {
errs() << "Recycler element size: " << Size << '\n'
<< "Recycler element alignment: " << Align << '\n'
<< "Number of elements free for recycling: " << FreeListSize << '\n';
}
}
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