Allocator.cpp revision 208954 
1//===--- Allocator.cpp - Simple memory allocation abstraction -------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the BumpPtrAllocator interface.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Support/Allocator.h"
15#include "llvm/System/DataTypes.h"
16#include "llvm/Support/Recycler.h"
17#include "llvm/Support/raw_ostream.h"
18#include "llvm/System/Memory.h"
19#include <cstring>
20
21namespace llvm {
22
23BumpPtrAllocator::BumpPtrAllocator(size_t size, size_t threshold,
24                                   SlabAllocator &allocator)
25    : SlabSize(size), SizeThreshold(threshold), Allocator(allocator),
26      CurSlab(0), BytesAllocated(0) { }
27
28BumpPtrAllocator::~BumpPtrAllocator() {
29  DeallocateSlabs(CurSlab);
30}
31
32/// AlignPtr - Align Ptr to Alignment bytes, rounding up.  Alignment should
33/// be a power of two.  This method rounds up, so AlignPtr(7, 4) == 8 and
34/// AlignPtr(8, 4) == 8.
35char *BumpPtrAllocator::AlignPtr(char *Ptr, size_t Alignment) {
36  assert(Alignment && (Alignment & (Alignment - 1)) == 0 &&
37         "Alignment is not a power of two!");
38
39  // Do the alignment.
40  return (char*)(((uintptr_t)Ptr + Alignment - 1) &
41                 ~(uintptr_t)(Alignment - 1));
42}
43
44/// StartNewSlab - Allocate a new slab and move the bump pointers over into
45/// the new slab.  Modifies CurPtr and End.
46void BumpPtrAllocator::StartNewSlab() {
47  MemSlab *NewSlab = Allocator.Allocate(SlabSize);
48  NewSlab->NextPtr = CurSlab;
49  CurSlab = NewSlab;
50  CurPtr = (char*)(CurSlab + 1);
51  End = ((char*)CurSlab) + CurSlab->Size;
52}
53
54/// DeallocateSlabs - Deallocate all memory slabs after and including this
55/// one.
56void BumpPtrAllocator::DeallocateSlabs(MemSlab *Slab) {
57  while (Slab) {
58    MemSlab *NextSlab = Slab->NextPtr;
59#ifndef NDEBUG
60    // Poison the memory so stale pointers crash sooner.  Note we must
61    // preserve the Size and NextPtr fields at the beginning.
62    sys::Memory::setRangeWritable(Slab + 1, Slab->Size - sizeof(MemSlab));
63    memset(Slab + 1, 0xCD, Slab->Size - sizeof(MemSlab));
64#endif
65    Allocator.Deallocate(Slab);
66    Slab = NextSlab;
67  }
68}
69
70/// Reset - Deallocate all but the current slab and reset the current pointer
71/// to the beginning of it, freeing all memory allocated so far.
72void BumpPtrAllocator::Reset() {
73  if (!CurSlab)
74    return;
75  DeallocateSlabs(CurSlab->NextPtr);
76  CurSlab->NextPtr = 0;
77  CurPtr = (char*)(CurSlab + 1);
78  End = ((char*)CurSlab) + CurSlab->Size;
79}
80
81/// Allocate - Allocate space at the specified alignment.
82///
83void *BumpPtrAllocator::Allocate(size_t Size, size_t Alignment) {
84  if (!CurSlab) // Start a new slab if we haven't allocated one already.
85    StartNewSlab();
86
87  // Keep track of how many bytes we've allocated.
88  BytesAllocated += Size;
89
90  // 0-byte alignment means 1-byte alignment.
91  if (Alignment == 0) Alignment = 1;
92
93  // Allocate the aligned space, going forwards from CurPtr.
94  char *Ptr = AlignPtr(CurPtr, Alignment);
95
96  // Check if we can hold it.
97  if (Ptr + Size <= End) {
98    CurPtr = Ptr + Size;
99    return Ptr;
100  }
101
102  // If Size is really big, allocate a separate slab for it.
103  size_t PaddedSize = Size + sizeof(MemSlab) + Alignment - 1;
104  if (PaddedSize > SizeThreshold) {
105    MemSlab *NewSlab = Allocator.Allocate(PaddedSize);
106
107    // Put the new slab after the current slab, since we are not allocating
108    // into it.
109    NewSlab->NextPtr = CurSlab->NextPtr;
110    CurSlab->NextPtr = NewSlab;
111
112    Ptr = AlignPtr((char*)(NewSlab + 1), Alignment);
113    assert((uintptr_t)Ptr + Size <= (uintptr_t)NewSlab + NewSlab->Size);
114    return Ptr;
115  }
116
117  // Otherwise, start a new slab and try again.
118  StartNewSlab();
119  Ptr = AlignPtr(CurPtr, Alignment);
120  CurPtr = Ptr + Size;
121  assert(CurPtr <= End && "Unable to allocate memory!");
122  return Ptr;
123}
124
125unsigned BumpPtrAllocator::GetNumSlabs() const {
126  unsigned NumSlabs = 0;
127  for (MemSlab *Slab = CurSlab; Slab != 0; Slab = Slab->NextPtr) {
128    ++NumSlabs;
129  }
130  return NumSlabs;
131}
132
133void BumpPtrAllocator::PrintStats() const {
134  unsigned NumSlabs = 0;
135  size_t TotalMemory = 0;
136  for (MemSlab *Slab = CurSlab; Slab != 0; Slab = Slab->NextPtr) {
137    TotalMemory += Slab->Size;
138    ++NumSlabs;
139  }
140
141  errs() << "\nNumber of memory regions: " << NumSlabs << '\n'
142         << "Bytes used: " << BytesAllocated << '\n'
143         << "Bytes allocated: " << TotalMemory << '\n'
144         << "Bytes wasted: " << (TotalMemory - BytesAllocated)
145         << " (includes alignment, etc)\n";
146}
147
148MallocSlabAllocator BumpPtrAllocator::DefaultSlabAllocator =
149  MallocSlabAllocator();
150
151SlabAllocator::~SlabAllocator() { }
152
153MallocSlabAllocator::~MallocSlabAllocator() { }
154
155MemSlab *MallocSlabAllocator::Allocate(size_t Size) {
156  MemSlab *Slab = (MemSlab*)Allocator.Allocate(Size, 0);
157  Slab->Size = Size;
158  Slab->NextPtr = 0;
159  return Slab;
160}
161
162void MallocSlabAllocator::Deallocate(MemSlab *Slab) {
163  Allocator.Deallocate(Slab);
164}
165
166void PrintRecyclerStats(size_t Size,
167                        size_t Align,
168                        size_t FreeListSize) {
169  errs() << "Recycler element size: " << Size << '\n'
170         << "Recycler element alignment: " << Align << '\n'
171         << "Number of elements free for recycling: " << FreeListSize << '\n';
172}
173
174}
175