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