lib/Support/Allocator.cpp

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