Re-committing changes from r76825 to BumpPtrAllocator with a fix and tests for

an off-by-one error.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76891 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 133 insertions, 105 deletions

diff --git a/lib/Support/Allocator.cpp b/lib/Support/Allocator.cpp
index db0d8f31e5..4e4a75ee58 100644
--- a/lib/Support/Allocator.cpp
+++ b/lib/Support/Allocator.cpp
@@ -12,130 +12,158 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/Allocator.h"
-#include "llvm/Support/Recycler.h"
 #include "llvm/Support/DataTypes.h"
+#include "llvm/Support/Recycler.h"
 #include "llvm/Support/Streams.h"
-#include <ostream>
-using namespace llvm;
+#include <cstring>
 
-//===----------------------------------------------------------------------===//
-// MemRegion class implementation
-//===----------------------------------------------------------------------===//
+namespace llvm {
 
-namespace {
-/// MemRegion - This is one chunk of the BumpPtrAllocator.
-class MemRegion {
-  unsigned RegionSize;
-  MemRegion *Next;
-  char *NextPtr;
-public:
-  void Init(unsigned size, unsigned Alignment, MemRegion *next) {
-    RegionSize = size;
-    Next = next;
-    NextPtr = (char*)(this+1);
-    
-    // Align NextPtr.
-    NextPtr = (char*)((intptr_t)(NextPtr+Alignment-1) &
-                      ~(intptr_t)(Alignment-1));
-  }
-  
-  const MemRegion *getNext() const { return Next; }
-  unsigned getNumBytesAllocated() const {
-    return NextPtr-(const char*)this;
-  }
-  
-  /// Allocate - Allocate and return at least the specified number of bytes.
-  ///
-  void *Allocate(size_t AllocSize, size_t Alignment, MemRegion **RegPtr) {
-    
-    char* Result = (char*) (((uintptr_t) (NextPtr+Alignment-1)) 
-                            & ~((uintptr_t) Alignment-1));
-
-    // Speculate the new value of NextPtr.
-    char* NextPtrTmp = Result + AllocSize;
-    
-    // If we are still within the current region, return Result.
-    if (unsigned (NextPtrTmp - (char*) this) <= RegionSize) {
-      NextPtr = NextPtrTmp;
-      return Result;
-    }
-    
-    // Otherwise, we have to allocate a new chunk.  Create one twice as big as
-    // this one.
-    MemRegion *NewRegion = (MemRegion *)malloc(RegionSize*2);
-    NewRegion->Init(RegionSize*2, Alignment, this);
-
-    // Update the current "first region" pointer  to point to the new region.
-    *RegPtr = NewRegion;
-    
-    // Try allocating from it now.
-    return NewRegion->Allocate(AllocSize, Alignment, RegPtr);
-  }
-  
-  /// Deallocate - Recursively release all memory for this and its next regions
-  /// to the system.
-  void Deallocate() {
-    MemRegion *next = Next;
-    free(this);
-    if (next)
-      next->Deallocate();
-  }
+BumpPtrAllocator::BumpPtrAllocator(size_t size, size_t threshold,
+                                   SlabAllocator &allocator)
+    : SlabSize(size), SizeThreshold(threshold), Allocator(allocator),
+      CurSlab(0), BytesAllocated(0) {
+  StartNewSlab();
+}
 
-  /// DeallocateAllButLast - Recursively release all memory for this and its
-  /// next regions to the system stopping at the last region in the list.
-  /// Returns the pointer to the last region.
-  MemRegion *DeallocateAllButLast() {
-    MemRegion *next = Next;
-    if (!next)
-      return this;
-    free(this);
-    return next->DeallocateAllButLast();
-  }
-};
+BumpPtrAllocator::~BumpPtrAllocator() {
+  DeallocateSlabs(CurSlab);
 }
 
-//===----------------------------------------------------------------------===//
-// BumpPtrAllocator class implementation
-//===----------------------------------------------------------------------===//
+/// 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!");
 
-BumpPtrAllocator::BumpPtrAllocator() {
-  TheMemory = malloc(4096);
-  ((MemRegion*)TheMemory)->Init(4096, 1, 0);
+  // Do the alignment.
+  return (char*)(((uintptr_t)Ptr + Alignment - 1) &
+                 ~(uintptr_t)(Alignment - 1));
 }
 
-BumpPtrAllocator::~BumpPtrAllocator() {
-  ((MemRegion*)TheMemory)->Deallocate();
+/// StartNewSlab - Allocate a new slab and move the bump pointers over into
+/// the new slab.  Modifies CurPtr and End.
+void BumpPtrAllocator::StartNewSlab() {
+  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.
+    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() {
-  MemRegion *MRP = (MemRegion*)TheMemory;
-  MRP = MRP->DeallocateAllButLast();
-  MRP->Init(4096, 1, 0);
-  TheMemory = MRP;
+  DeallocateSlabs(CurSlab->NextPtr);
+  CurSlab->NextPtr = 0;
+  CurPtr = (char*)(CurSlab + 1);
+  End = ((char*)CurSlab) + CurSlab->Size;
 }
 
-void *BumpPtrAllocator::Allocate(size_t Size, size_t Align) {
-  MemRegion *MRP = (MemRegion*)TheMemory;
-  void *Ptr = MRP->Allocate(Size, Align, &MRP);
-  TheMemory = MRP;
+/// Allocate - Allocate space at the specified alignment.
+///
+void *BumpPtrAllocator::Allocate(size_t Size, size_t Alignment) {
+  // 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.
+  if (Size > SizeThreshold) {
+    size_t PaddedSize = Size + sizeof(MemSlab) + Alignment - 1;
+    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 BytesUsed = 0;
-  unsigned NumRegions = 0;
-  const MemRegion *R = (MemRegion*)TheMemory;
-  for (; R; R = R->getNext(), ++NumRegions)
-    BytesUsed += R->getNumBytesAllocated();
-
-  cerr << "\nNumber of memory regions: " << NumRegions << "\n";
-  cerr << "Bytes allocated: " << BytesUsed << "\n";
+  unsigned NumSlabs = 0;
+  size_t TotalMemory = 0;
+  for (MemSlab *Slab = CurSlab; Slab != 0; Slab = Slab->NextPtr) {
+    TotalMemory += Slab->Size;
+    ++NumSlabs;
+  }
+
+  cerr << "\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) {
+  cerr << "Recycler element size: " << Size << '\n'
+       << "Recycler element alignment: " << Align << '\n'
+       << "Number of elements free for recycling: " << FreeListSize << '\n';
 }
 
-void llvm::PrintRecyclerStats(size_t Size,
-                              size_t Align,
-                              size_t FreeListSize) {
-  cerr << "Recycler element size: " << Size << '\n';
-  cerr << "Recycler element alignment: " << Align << '\n';
-  cerr << "Number of elements free for recycling: " << FreeListSize << '\n';
 }