Add a new llvm::Allocator abstraction, which will be used by a container

I'm about to add.  This is similar to, but necessarily different than, the
STL allocator class.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31285 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/Allocator.cpp

@@ -0,0 +1,106 @@
+//===--- Allocator.cpp - Simple memory allocation abstraction -------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Chris Lattner and 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 <iostream>
+using namespace llvm;
+
+//===----------------------------------------------------------------------===//
+// MemRegion class implementation
+//===----------------------------------------------------------------------===//
+
+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(unsigned AllocSize, unsigned Alignment, MemRegion **RegPtr) {
+    // Round size up to an even multiple of the alignment.
+    AllocSize = (AllocSize+Alignment-1) & ~(Alignment-1);
+    
+    // If there is space in this region, return it.
+    if (unsigned(NextPtr+AllocSize-(char*)this) <= RegionSize) {
+      void *Result = NextPtr;
+      NextPtr += AllocSize;
+      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 - Release all memory for this region to the system.
+  ///
+  void Deallocate() {
+    MemRegion *next = Next;
+    free(this);
+    if (next)
+      next->Deallocate();
+  }
+};
+}
+
+//===----------------------------------------------------------------------===//
+// BumpPtrAllocator class implementation
+//===----------------------------------------------------------------------===//
+
+BumpPtrAllocator::BumpPtrAllocator() {
+  TheMemory = malloc(4096);
+  ((MemRegion*)TheMemory)->Init(4096, 1, 0);
+}
+
+BumpPtrAllocator::~BumpPtrAllocator() {
+  ((MemRegion*)TheMemory)->Deallocate();
+}
+
+void *BumpPtrAllocator::Allocate(unsigned Size, unsigned Align) {
+  return ((MemRegion*)TheMemory)->Allocate(Size, Align,(MemRegion**)&TheMemory);
+}
+
+void BumpPtrAllocator::PrintStats() const {
+  unsigned BytesUsed = 0;
+  unsigned NumRegions = 0;
+  const MemRegion *R = (MemRegion*)TheMemory;
+  for (; R; R = R->getNext(), ++NumRegions)
+    BytesUsed += R->getNumBytesAllocated();
+
+  std::cerr << "\nNumber of memory regions: " << NumRegions << "\n";
+  std::cerr << "Bytes allocated: " << BytesUsed << "\n";
+}