lib/ExecutionEngine/JIT/JITMemoryManager.cpp - platform/external/llvm - Git at Google

 //===-- JITMemoryManager.cpp - Memory Allocator for JIT'd code ------------===//
 //
 //                     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 defines the DefaultJITMemoryManager class.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/ExecutionEngine/JITMemoryManager.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/System/Memory.h"
 #include <map>
 #include <vector>
 #include <cassert>
 using namespace llvm;


 JITMemoryManager::~JITMemoryManager() {}

 //===----------------------------------------------------------------------===//
 // Memory Block Implementation.
 //===----------------------------------------------------------------------===//

 namespace {
   /// MemoryRangeHeader - For a range of memory, this is the header that we put
   /// on the block of memory.  It is carefully crafted to be one word of memory.
   /// Allocated blocks have just this header, free'd blocks have FreeRangeHeader
   /// which starts with this.
   struct FreeRangeHeader;
   struct MemoryRangeHeader {
     /// ThisAllocated - This is true if this block is currently allocated.  If
     /// not, this can be converted to a FreeRangeHeader.
     unsigned ThisAllocated : 1;

     /// PrevAllocated - Keep track of whether the block immediately before us is
     /// allocated.  If not, the word immediately before this header is the size
     /// of the previous block.
     unsigned PrevAllocated : 1;

     /// BlockSize - This is the size in bytes of this memory block,
     /// including this header.
     uintptr_t BlockSize : (sizeof(intptr_t)*8 - 2);


     /// getBlockAfter - Return the memory block immediately after this one.
     ///
     MemoryRangeHeader &getBlockAfter() const {
       return *(MemoryRangeHeader*)((char*)this+BlockSize);
     }

     /// getFreeBlockBefore - If the block before this one is free, return it,
     /// otherwise return null.
     FreeRangeHeader *getFreeBlockBefore() const {
       if (PrevAllocated) return 0;
       intptr_t PrevSize = ((intptr_t *)this)[-1];
       return (FreeRangeHeader*)((char*)this-PrevSize);
     }

     /// FreeBlock - Turn an allocated block into a free block, adjusting
     /// bits in the object headers, and adding an end of region memory block.
     FreeRangeHeader *FreeBlock(FreeRangeHeader *FreeList);

     /// TrimAllocationToSize - If this allocated block is significantly larger
     /// than NewSize, split it into two pieces (where the former is NewSize
     /// bytes, including the header), and add the new block to the free list.
     FreeRangeHeader *TrimAllocationToSize(FreeRangeHeader *FreeList,
                                           uint64_t NewSize);
   };

   /// FreeRangeHeader - For a memory block that isn't already allocated, this
   /// keeps track of the current block and has a pointer to the next free block.
   /// Free blocks are kept on a circularly linked list.
   struct FreeRangeHeader : public MemoryRangeHeader {
     FreeRangeHeader *Prev;
     FreeRangeHeader *Next;

     /// getMinBlockSize - Get the minimum size for a memory block.  Blocks
     /// smaller than this size cannot be created.
     static unsigned getMinBlockSize() {
       return sizeof(FreeRangeHeader)+sizeof(intptr_t);
     }

     /// SetEndOfBlockSizeMarker - The word at the end of every free block is
     /// known to be the size of the free block.  Set it for this block.
     void SetEndOfBlockSizeMarker() {
       void *EndOfBlock = (char*)this + BlockSize;
       ((intptr_t *)EndOfBlock)[-1] = BlockSize;
     }

     FreeRangeHeader *RemoveFromFreeList() {
       assert(Next->Prev == this && Prev->Next == this && "Freelist broken!");
       Next->Prev = Prev;
       return Prev->Next = Next;
     }

     void AddToFreeList(FreeRangeHeader *FreeList) {
       Next = FreeList;
       Prev = FreeList->Prev;
       Prev->Next = this;
       Next->Prev = this;
     }

     /// GrowBlock - The block after this block just got deallocated.  Merge it
     /// into the current block.
     void GrowBlock(uintptr_t NewSize);

     /// AllocateBlock - Mark this entire block allocated, updating freelists
     /// etc.  This returns a pointer to the circular free-list.
     FreeRangeHeader *AllocateBlock();
   };
 }


 /// AllocateBlock - Mark this entire block allocated, updating freelists
 /// etc.  This returns a pointer to the circular free-list.
 FreeRangeHeader *FreeRangeHeader::AllocateBlock() {
   assert(!ThisAllocated && !getBlockAfter().PrevAllocated &&
          "Cannot allocate an allocated block!");
   // Mark this block allocated.
   ThisAllocated = 1;
   getBlockAfter().PrevAllocated = 1;

   // Remove it from the free list.
   return RemoveFromFreeList();
 }

 /// FreeBlock - Turn an allocated block into a free block, adjusting
 /// bits in the object headers, and adding an end of region memory block.
 /// If possible, coalesce this block with neighboring blocks.  Return the
 /// FreeRangeHeader to allocate from.
 FreeRangeHeader *MemoryRangeHeader::FreeBlock(FreeRangeHeader *FreeList) {
   MemoryRangeHeader *FollowingBlock = &getBlockAfter();
   assert(ThisAllocated && "This block is already allocated!");
   assert(FollowingBlock->PrevAllocated && "Flags out of sync!");

   FreeRangeHeader *FreeListToReturn = FreeList;

   // If the block after this one is free, merge it into this block.
   if (!FollowingBlock->ThisAllocated) {
     FreeRangeHeader &FollowingFreeBlock = *(FreeRangeHeader *)FollowingBlock;
     // "FreeList" always needs to be a valid free block.  If we're about to
     // coalesce with it, update our notion of what the free list is.
     if (&FollowingFreeBlock == FreeList) {
       FreeList = FollowingFreeBlock.Next;
       FreeListToReturn = 0;
       assert(&FollowingFreeBlock != FreeList && "No tombstone block?");
     }
     FollowingFreeBlock.RemoveFromFreeList();

     // Include the following block into this one.
     BlockSize += FollowingFreeBlock.BlockSize;
     FollowingBlock = &FollowingFreeBlock.getBlockAfter();

     // Tell the block after the block we are coalescing that this block is
     // allocated.
     FollowingBlock->PrevAllocated = 1;
   }

   assert(FollowingBlock->ThisAllocated && "Missed coalescing?");

   if (FreeRangeHeader *PrevFreeBlock = getFreeBlockBefore()) {
     PrevFreeBlock->GrowBlock(PrevFreeBlock->BlockSize + BlockSize);
     return FreeListToReturn ? FreeListToReturn : PrevFreeBlock;
   }

   // Otherwise, mark this block free.
   FreeRangeHeader &FreeBlock = *(FreeRangeHeader*)this;
   FollowingBlock->PrevAllocated = 0;
   FreeBlock.ThisAllocated = 0;

   // Link this into the linked list of free blocks.
   FreeBlock.AddToFreeList(FreeList);

   // Add a marker at the end of the block, indicating the size of this free
   // block.
   FreeBlock.SetEndOfBlockSizeMarker();
   return FreeListToReturn ? FreeListToReturn : &FreeBlock;
 }

 /// GrowBlock - The block after this block just got deallocated.  Merge it
 /// into the current block.
 void FreeRangeHeader::GrowBlock(uintptr_t NewSize) {
   assert(NewSize > BlockSize && "Not growing block?");
   BlockSize = NewSize;
   SetEndOfBlockSizeMarker();
   getBlockAfter().PrevAllocated = 0;
 }

 /// TrimAllocationToSize - If this allocated block is significantly larger
 /// than NewSize, split it into two pieces (where the former is NewSize
 /// bytes, including the header), and add the new block to the free list.
 FreeRangeHeader *MemoryRangeHeader::
 TrimAllocationToSize(FreeRangeHeader *FreeList, uint64_t NewSize) {
   assert(ThisAllocated && getBlockAfter().PrevAllocated &&
          "Cannot deallocate part of an allocated block!");

   // Round up size for alignment of header.
   unsigned HeaderAlign = __alignof(FreeRangeHeader);
   NewSize = (NewSize+ (HeaderAlign-1)) & ~(HeaderAlign-1);

   // Size is now the size of the block we will remove from the start of the
   // current block.
   assert(NewSize <= BlockSize &&
          "Allocating more space from this block than exists!");

   // If splitting this block will cause the remainder to be too small, do not
   // split the block.
   if (BlockSize <= NewSize+FreeRangeHeader::getMinBlockSize())
     return FreeList;

   // Otherwise, we splice the required number of bytes out of this block, form
   // a new block immediately after it, then mark this block allocated.
   MemoryRangeHeader &FormerNextBlock = getBlockAfter();

   // Change the size of this block.
   BlockSize = NewSize;

   // Get the new block we just sliced out and turn it into a free block.
   FreeRangeHeader &NewNextBlock = (FreeRangeHeader &)getBlockAfter();
   NewNextBlock.BlockSize = (char*)&FormerNextBlock - (char*)&NewNextBlock;
   NewNextBlock.ThisAllocated = 0;
   NewNextBlock.PrevAllocated = 1;
   NewNextBlock.SetEndOfBlockSizeMarker();
   FormerNextBlock.PrevAllocated = 0;
   NewNextBlock.AddToFreeList(FreeList);
   return &NewNextBlock;
 }

 //===----------------------------------------------------------------------===//
 // Memory Block Implementation.
 //===----------------------------------------------------------------------===//

 namespace {
   /// DefaultJITMemoryManager - Manage memory for the JIT code generation.
   /// This splits a large block of MAP_NORESERVE'd memory into two
   /// sections, one for function stubs, one for the functions themselves.  We
   /// have to do this because we may need to emit a function stub while in the
   /// middle of emitting a function, and we don't know how large the function we
   /// are emitting is.
   class VISIBILITY_HIDDEN DefaultJITMemoryManager : public JITMemoryManager {
     std::vector<sys::MemoryBlock> Blocks; // Memory blocks allocated by the JIT
     FreeRangeHeader *FreeMemoryList;      // Circular list of free blocks.

     // When emitting code into a memory block, this is the block.
     MemoryRangeHeader *CurBlock;

     unsigned char *CurStubPtr, *StubBase;
     unsigned char *GOTBase;      // Target Specific reserved memory

     // Centralize memory block allocation.
     sys::MemoryBlock getNewMemoryBlock(unsigned size);

     std::map<const Function*, MemoryRangeHeader*> FunctionBlocks;
   public:
     DefaultJITMemoryManager();
     ~DefaultJITMemoryManager();

     void AllocateGOT();

     unsigned char *allocateStub(unsigned StubSize, unsigned Alignment);

     /// startFunctionBody - When a function starts, allocate a block of free
     /// executable memory, returning a pointer to it and its actual size.
     unsigned char *startFunctionBody(const Function *F, uintptr_t &ActualSize) {
       CurBlock = FreeMemoryList;

       // Allocate the entire memory block.
       FreeMemoryList = FreeMemoryList->AllocateBlock();
       ActualSize = CurBlock->BlockSize-sizeof(MemoryRangeHeader);
       return (unsigned char *)(CurBlock+1);
     }

     /// endFunctionBody - The function F is now allocated, and takes the memory
     /// in the range [FunctionStart,FunctionEnd).
     void endFunctionBody(const Function *F, unsigned char *FunctionStart,
                          unsigned char *FunctionEnd) {
       assert(FunctionEnd > FunctionStart);
       assert(FunctionStart == (unsigned char *)(CurBlock+1) &&
              "Mismatched function start/end!");

       uintptr_t BlockSize = FunctionEnd - (unsigned char *)CurBlock;
       FunctionBlocks[F] = CurBlock;

       // Release the memory at the end of this block that isn't needed.
       FreeMemoryList =CurBlock->TrimAllocationToSize(FreeMemoryList, BlockSize);
     }

     unsigned char *getGOTBase() const {
       return GOTBase;
     }

     /// deallocateMemForFunction - Deallocate all memory for the specified
     /// function body.
     void deallocateMemForFunction(const Function *F) {
       std::map<const Function*, MemoryRangeHeader*>::iterator
         I = FunctionBlocks.find(F);
       if (I == FunctionBlocks.end()) return;

       // Find the block that is allocated for this function.
       MemoryRangeHeader *MemRange = I->second;
       assert(MemRange->ThisAllocated && "Block isn't allocated!");

       // Fill the buffer with garbage!
 #ifndef NDEBUG
       memset(MemRange+1, 0xCD, MemRange->BlockSize-sizeof(*MemRange));
 #endif

       // Free the memory.
       FreeMemoryList = MemRange->FreeBlock(FreeMemoryList);

       // Finally, remove this entry from FunctionBlocks.
       FunctionBlocks.erase(I);
     }
   };
 }

 DefaultJITMemoryManager::DefaultJITMemoryManager() {
   // Allocate a 16M block of memory for functions.
   sys::MemoryBlock MemBlock = getNewMemoryBlock(16 << 20);

   unsigned char *MemBase = reinterpret_cast<unsigned char*>(MemBlock.base());

   // Allocate stubs backwards from the base, allocate functions forward
   // from the base.
   StubBase   = MemBase;
   CurStubPtr = MemBase + 512*1024; // Use 512k for stubs, working backwards.

   // We set up the memory chunk with 4 mem regions, like this:
   //  [ START
   //    [ Free      #0 ] -> Large space to allocate functions from.
   //    [ Allocated #1 ] -> Tiny space to separate regions.
   //    [ Free      #2 ] -> Tiny space so there is always at least 1 free block.
   //    [ Allocated #3 ] -> Tiny space to prevent looking past end of block.
   //  END ]
   //
   // The last three blocks are never deallocated or touched.

   // Add MemoryRangeHeader to the end of the memory region, indicating that
   // the space after the block of memory is allocated.  This is block #3.
   MemoryRangeHeader *Mem3 = (MemoryRangeHeader*)(MemBase+MemBlock.size())-1;
   Mem3->ThisAllocated = 1;
   Mem3->PrevAllocated = 0;
   Mem3->BlockSize     = 0;

   /// Add a tiny free region so that the free list always has one entry.
   FreeRangeHeader *Mem2 =
     (FreeRangeHeader *)(((char*)Mem3)-FreeRangeHeader::getMinBlockSize());
   Mem2->ThisAllocated = 0;
   Mem2->PrevAllocated = 1;
   Mem2->BlockSize     = FreeRangeHeader::getMinBlockSize();
   Mem2->SetEndOfBlockSizeMarker();
   Mem2->Prev = Mem2;   // Mem2 *is* the free list for now.
   Mem2->Next = Mem2;

   /// Add a tiny allocated region so that Mem2 is never coalesced away.
   MemoryRangeHeader *Mem1 = (MemoryRangeHeader*)Mem2-1;
   Mem1->ThisAllocated = 1;
   Mem1->PrevAllocated = 0;
   Mem1->BlockSize     = (char*)Mem2 - (char*)Mem1;

   // Add a FreeRangeHeader to the start of the function body region, indicating
   // that the space is free.  Mark the previous block allocated so we never look
   // at it.
   FreeRangeHeader *Mem0 = (FreeRangeHeader*)CurStubPtr;
   Mem0->ThisAllocated = 0;
   Mem0->PrevAllocated = 1;
   Mem0->BlockSize = (char*)Mem1-(char*)Mem0;
   Mem0->SetEndOfBlockSizeMarker();
   Mem0->AddToFreeList(Mem2);

   // Start out with the freelist pointing to Mem0.
   FreeMemoryList = Mem0;

   GOTBase = NULL;
 }

 void DefaultJITMemoryManager::AllocateGOT() {
   assert(GOTBase == 0 && "Cannot allocate the got multiple times");
   GOTBase = new unsigned char[sizeof(void*) * 8192];
   HasGOT = true;
 }


 DefaultJITMemoryManager::~DefaultJITMemoryManager() {
   for (unsigned i = 0, e = Blocks.size(); i != e; ++i)
     sys::Memory::ReleaseRWX(Blocks[i]);

   delete[] GOTBase;
   Blocks.clear();
 }

 unsigned char *DefaultJITMemoryManager::allocateStub(unsigned StubSize,
                                                      unsigned Alignment) {
   CurStubPtr -= StubSize;
   CurStubPtr = (unsigned char*)(((intptr_t)CurStubPtr) &
                                 ~(intptr_t)(Alignment-1));
   if (CurStubPtr < StubBase) {
     // FIXME: allocate a new block
     fprintf(stderr, "JIT ran out of memory for function stubs!\n");
     abort();
   }
   return CurStubPtr;
 }

 sys::MemoryBlock DefaultJITMemoryManager::getNewMemoryBlock(unsigned size) {
   // Allocate a new block close to the last one.
   const sys::MemoryBlock *BOld = Blocks.empty() ? 0 : &Blocks.front();
   std::string ErrMsg;
   sys::MemoryBlock B = sys::Memory::AllocateRWX(size, BOld, &ErrMsg);
   if (B.base() == 0) {
     fprintf(stderr,
             "Allocation failed when allocating new memory in the JIT\n%s\n",
             ErrMsg.c_str());
     abort();
   }
   Blocks.push_back(B);
   return B;
 }


 JITMemoryManager *JITMemoryManager::CreateDefaultMemManager() {
   return new DefaultJITMemoryManager();
 }
	//===-- JITMemoryManager.cpp - Memory Allocator for JIT'd code ------------===//
	//
	// 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 defines the DefaultJITMemoryManager class.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/ExecutionEngine/JITMemoryManager.h"
	#include "llvm/Support/Compiler.h"
	#include "llvm/System/Memory.h"
	#include <map>
	#include <vector>
	#include <cassert>
	using namespace llvm;


	JITMemoryManager::~JITMemoryManager() {}

	//===----------------------------------------------------------------------===//
	// Memory Block Implementation.
	//===----------------------------------------------------------------------===//

	namespace {
	/// MemoryRangeHeader - For a range of memory, this is the header that we put
	/// on the block of memory. It is carefully crafted to be one word of memory.
	/// Allocated blocks have just this header, free'd blocks have FreeRangeHeader
	/// which starts with this.
	struct FreeRangeHeader;
	struct MemoryRangeHeader {
	/// ThisAllocated - This is true if this block is currently allocated. If
	/// not, this can be converted to a FreeRangeHeader.
	unsigned ThisAllocated : 1;

	/// PrevAllocated - Keep track of whether the block immediately before us is
	/// allocated. If not, the word immediately before this header is the size
	/// of the previous block.
	unsigned PrevAllocated : 1;

	/// BlockSize - This is the size in bytes of this memory block,
	/// including this header.
	uintptr_t BlockSize : (sizeof(intptr_t)*8 - 2);


	/// getBlockAfter - Return the memory block immediately after this one.
	///
	MemoryRangeHeader &getBlockAfter() const {
	return (MemoryRangeHeader)((char*)this+BlockSize);
	}

	/// getFreeBlockBefore - If the block before this one is free, return it,
	/// otherwise return null.
	FreeRangeHeader *getFreeBlockBefore() const {
	if (PrevAllocated) return 0;
	intptr_t PrevSize = ((intptr_t *)this)[-1];
	return (FreeRangeHeader)((char)this-PrevSize);
	}

	/// FreeBlock - Turn an allocated block into a free block, adjusting
	/// bits in the object headers, and adding an end of region memory block.
	FreeRangeHeader FreeBlock(FreeRangeHeader FreeList);

	/// TrimAllocationToSize - If this allocated block is significantly larger
	/// than NewSize, split it into two pieces (where the former is NewSize
	/// bytes, including the header), and add the new block to the free list.
	FreeRangeHeader TrimAllocationToSize(FreeRangeHeader FreeList,
	uint64_t NewSize);
	};

	/// FreeRangeHeader - For a memory block that isn't already allocated, this
	/// keeps track of the current block and has a pointer to the next free block.
	/// Free blocks are kept on a circularly linked list.
	struct FreeRangeHeader : public MemoryRangeHeader {
	FreeRangeHeader *Prev;
	FreeRangeHeader *Next;

	/// getMinBlockSize - Get the minimum size for a memory block. Blocks
	/// smaller than this size cannot be created.
	static unsigned getMinBlockSize() {
	return sizeof(FreeRangeHeader)+sizeof(intptr_t);
	}

	/// SetEndOfBlockSizeMarker - The word at the end of every free block is
	/// known to be the size of the free block. Set it for this block.
	void SetEndOfBlockSizeMarker() {
	void EndOfBlock = (char)this + BlockSize;
	((intptr_t *)EndOfBlock)[-1] = BlockSize;
	}

	FreeRangeHeader *RemoveFromFreeList() {
	assert(Next->Prev == this && Prev->Next == this && "Freelist broken!");
	Next->Prev = Prev;
	return Prev->Next = Next;
	}

	void AddToFreeList(FreeRangeHeader *FreeList) {
	Next = FreeList;
	Prev = FreeList->Prev;
	Prev->Next = this;
	Next->Prev = this;
	}

	/// GrowBlock - The block after this block just got deallocated. Merge it
	/// into the current block.
	void GrowBlock(uintptr_t NewSize);

	/// AllocateBlock - Mark this entire block allocated, updating freelists
	/// etc. This returns a pointer to the circular free-list.
	FreeRangeHeader *AllocateBlock();
	};
	}


	/// AllocateBlock - Mark this entire block allocated, updating freelists
	/// etc. This returns a pointer to the circular free-list.
	FreeRangeHeader *FreeRangeHeader::AllocateBlock() {
	assert(!ThisAllocated && !getBlockAfter().PrevAllocated &&
	"Cannot allocate an allocated block!");
	// Mark this block allocated.
	ThisAllocated = 1;
	getBlockAfter().PrevAllocated = 1;

	// Remove it from the free list.
	return RemoveFromFreeList();
	}

	/// FreeBlock - Turn an allocated block into a free block, adjusting
	/// bits in the object headers, and adding an end of region memory block.
	/// If possible, coalesce this block with neighboring blocks. Return the
	/// FreeRangeHeader to allocate from.
	FreeRangeHeader MemoryRangeHeader::FreeBlock(FreeRangeHeader FreeList) {
	MemoryRangeHeader *FollowingBlock = &getBlockAfter();
	assert(ThisAllocated && "This block is already allocated!");
	assert(FollowingBlock->PrevAllocated && "Flags out of sync!");

	FreeRangeHeader *FreeListToReturn = FreeList;

	// If the block after this one is free, merge it into this block.
	if (!FollowingBlock->ThisAllocated) {
	FreeRangeHeader &FollowingFreeBlock = (FreeRangeHeader )FollowingBlock;
	// "FreeList" always needs to be a valid free block. If we're about to
	// coalesce with it, update our notion of what the free list is.
	if (&FollowingFreeBlock == FreeList) {
	FreeList = FollowingFreeBlock.Next;
	FreeListToReturn = 0;
	assert(&FollowingFreeBlock != FreeList && "No tombstone block?");
	}
	FollowingFreeBlock.RemoveFromFreeList();

	// Include the following block into this one.
	BlockSize += FollowingFreeBlock.BlockSize;
	FollowingBlock = &FollowingFreeBlock.getBlockAfter();

	// Tell the block after the block we are coalescing that this block is
	// allocated.
	FollowingBlock->PrevAllocated = 1;
	}

	assert(FollowingBlock->ThisAllocated && "Missed coalescing?");

	if (FreeRangeHeader *PrevFreeBlock = getFreeBlockBefore()) {
	PrevFreeBlock->GrowBlock(PrevFreeBlock->BlockSize + BlockSize);
	return FreeListToReturn ? FreeListToReturn : PrevFreeBlock;
	}

	// Otherwise, mark this block free.
	FreeRangeHeader &FreeBlock = (FreeRangeHeader)this;
	FollowingBlock->PrevAllocated = 0;
	FreeBlock.ThisAllocated = 0;

	// Link this into the linked list of free blocks.
	FreeBlock.AddToFreeList(FreeList);

	// Add a marker at the end of the block, indicating the size of this free
	// block.
	FreeBlock.SetEndOfBlockSizeMarker();
	return FreeListToReturn ? FreeListToReturn : &FreeBlock;
	}

	/// GrowBlock - The block after this block just got deallocated. Merge it
	/// into the current block.
	void FreeRangeHeader::GrowBlock(uintptr_t NewSize) {
	assert(NewSize > BlockSize && "Not growing block?");
	BlockSize = NewSize;
	SetEndOfBlockSizeMarker();
	getBlockAfter().PrevAllocated = 0;
	}

	/// TrimAllocationToSize - If this allocated block is significantly larger
	/// than NewSize, split it into two pieces (where the former is NewSize
	/// bytes, including the header), and add the new block to the free list.
	FreeRangeHeader *MemoryRangeHeader::
	TrimAllocationToSize(FreeRangeHeader *FreeList, uint64_t NewSize) {
	assert(ThisAllocated && getBlockAfter().PrevAllocated &&
	"Cannot deallocate part of an allocated block!");

	// Round up size for alignment of header.
	unsigned HeaderAlign = __alignof(FreeRangeHeader);
	NewSize = (NewSize+ (HeaderAlign-1)) & ~(HeaderAlign-1);

	// Size is now the size of the block we will remove from the start of the
	// current block.
	assert(NewSize <= BlockSize &&
	"Allocating more space from this block than exists!");

	// If splitting this block will cause the remainder to be too small, do not
	// split the block.
	if (BlockSize <= NewSize+FreeRangeHeader::getMinBlockSize())
	return FreeList;

	// Otherwise, we splice the required number of bytes out of this block, form
	// a new block immediately after it, then mark this block allocated.
	MemoryRangeHeader &FormerNextBlock = getBlockAfter();

	// Change the size of this block.
	BlockSize = NewSize;

	// Get the new block we just sliced out and turn it into a free block.
	FreeRangeHeader &NewNextBlock = (FreeRangeHeader &)getBlockAfter();
	NewNextBlock.BlockSize = (char)&FormerNextBlock - (char)&NewNextBlock;
	NewNextBlock.ThisAllocated = 0;
	NewNextBlock.PrevAllocated = 1;
	NewNextBlock.SetEndOfBlockSizeMarker();
	FormerNextBlock.PrevAllocated = 0;
	NewNextBlock.AddToFreeList(FreeList);
	return &NewNextBlock;
	}

	//===----------------------------------------------------------------------===//
	// Memory Block Implementation.
	//===----------------------------------------------------------------------===//

	namespace {
	/// DefaultJITMemoryManager - Manage memory for the JIT code generation.
	/// This splits a large block of MAP_NORESERVE'd memory into two
	/// sections, one for function stubs, one for the functions themselves. We
	/// have to do this because we may need to emit a function stub while in the
	/// middle of emitting a function, and we don't know how large the function we
	/// are emitting is.
	class VISIBILITY_HIDDEN DefaultJITMemoryManager : public JITMemoryManager {
	std::vector<sys::MemoryBlock> Blocks; // Memory blocks allocated by the JIT
	FreeRangeHeader *FreeMemoryList; // Circular list of free blocks.

	// When emitting code into a memory block, this is the block.
	MemoryRangeHeader *CurBlock;

	unsigned char CurStubPtr, StubBase;
	unsigned char *GOTBase; // Target Specific reserved memory

	// Centralize memory block allocation.
	sys::MemoryBlock getNewMemoryBlock(unsigned size);

	std::map<const Function, MemoryRangeHeader> FunctionBlocks;
	public:
	DefaultJITMemoryManager();
	~DefaultJITMemoryManager();

	void AllocateGOT();

	unsigned char *allocateStub(unsigned StubSize, unsigned Alignment);

	/// startFunctionBody - When a function starts, allocate a block of free
	/// executable memory, returning a pointer to it and its actual size.
	unsigned char startFunctionBody(const Function F, uintptr_t &ActualSize) {
	CurBlock = FreeMemoryList;

	// Allocate the entire memory block.
	FreeMemoryList = FreeMemoryList->AllocateBlock();
	ActualSize = CurBlock->BlockSize-sizeof(MemoryRangeHeader);
	return (unsigned char *)(CurBlock+1);
	}

	/// endFunctionBody - The function F is now allocated, and takes the memory
	/// in the range [FunctionStart,FunctionEnd).
	void endFunctionBody(const Function F, unsigned char FunctionStart,
	unsigned char *FunctionEnd) {
	assert(FunctionEnd > FunctionStart);
	assert(FunctionStart == (unsigned char *)(CurBlock+1) &&
	"Mismatched function start/end!");

	uintptr_t BlockSize = FunctionEnd - (unsigned char *)CurBlock;
	FunctionBlocks[F] = CurBlock;

	// Release the memory at the end of this block that isn't needed.
	FreeMemoryList =CurBlock->TrimAllocationToSize(FreeMemoryList, BlockSize);
	}

	unsigned char *getGOTBase() const {
	return GOTBase;
	}

	/// deallocateMemForFunction - Deallocate all memory for the specified
	/// function body.
	void deallocateMemForFunction(const Function *F) {
	std::map<const Function, MemoryRangeHeader>::iterator
	I = FunctionBlocks.find(F);
	if (I == FunctionBlocks.end()) return;

	// Find the block that is allocated for this function.
	MemoryRangeHeader *MemRange = I->second;
	assert(MemRange->ThisAllocated && "Block isn't allocated!");

	// Fill the buffer with garbage!
	#ifndef NDEBUG
	memset(MemRange+1, 0xCD, MemRange->BlockSize-sizeof(*MemRange));
	#endif

	// Free the memory.
	FreeMemoryList = MemRange->FreeBlock(FreeMemoryList);

	// Finally, remove this entry from FunctionBlocks.
	FunctionBlocks.erase(I);
	}
	};
	}

	DefaultJITMemoryManager::DefaultJITMemoryManager() {
	// Allocate a 16M block of memory for functions.
	sys::MemoryBlock MemBlock = getNewMemoryBlock(16 << 20);

	unsigned char MemBase = reinterpret_cast<unsigned char>(MemBlock.base());

	// Allocate stubs backwards from the base, allocate functions forward
	// from the base.
	StubBase = MemBase;
	CurStubPtr = MemBase + 512*1024; // Use 512k for stubs, working backwards.

	// We set up the memory chunk with 4 mem regions, like this:
	// [ START
	// [ Free #0 ] -> Large space to allocate functions from.
	// [ Allocated #1 ] -> Tiny space to separate regions.
	// [ Free #2 ] -> Tiny space so there is always at least 1 free block.
	// [ Allocated #3 ] -> Tiny space to prevent looking past end of block.
	// END ]
	//
	// The last three blocks are never deallocated or touched.

	// Add MemoryRangeHeader to the end of the memory region, indicating that
	// the space after the block of memory is allocated. This is block #3.
	MemoryRangeHeader Mem3 = (MemoryRangeHeader)(MemBase+MemBlock.size())-1;
	Mem3->ThisAllocated = 1;
	Mem3->PrevAllocated = 0;
	Mem3->BlockSize = 0;

	/// Add a tiny free region so that the free list always has one entry.
	FreeRangeHeader *Mem2 =
	(FreeRangeHeader )(((char)Mem3)-FreeRangeHeader::getMinBlockSize());
	Mem2->ThisAllocated = 0;
	Mem2->PrevAllocated = 1;
	Mem2->BlockSize = FreeRangeHeader::getMinBlockSize();
	Mem2->SetEndOfBlockSizeMarker();
	Mem2->Prev = Mem2; // Mem2 is the free list for now.
	Mem2->Next = Mem2;

	/// Add a tiny allocated region so that Mem2 is never coalesced away.
	MemoryRangeHeader Mem1 = (MemoryRangeHeader)Mem2-1;
	Mem1->ThisAllocated = 1;
	Mem1->PrevAllocated = 0;
	Mem1->BlockSize = (char)Mem2 - (char)Mem1;

	// Add a FreeRangeHeader to the start of the function body region, indicating
	// that the space is free. Mark the previous block allocated so we never look
	// at it.
	FreeRangeHeader Mem0 = (FreeRangeHeader)CurStubPtr;
	Mem0->ThisAllocated = 0;
	Mem0->PrevAllocated = 1;
	Mem0->BlockSize = (char)Mem1-(char)Mem0;
	Mem0->SetEndOfBlockSizeMarker();
	Mem0->AddToFreeList(Mem2);

	// Start out with the freelist pointing to Mem0.
	FreeMemoryList = Mem0;

	GOTBase = NULL;
	}

	void DefaultJITMemoryManager::AllocateGOT() {
	assert(GOTBase == 0 && "Cannot allocate the got multiple times");
	GOTBase = new unsigned char[sizeof(void) 8192];
	HasGOT = true;
	}


	DefaultJITMemoryManager::~DefaultJITMemoryManager() {
	for (unsigned i = 0, e = Blocks.size(); i != e; ++i)
	sys::Memory::ReleaseRWX(Blocks[i]);

	delete[] GOTBase;
	Blocks.clear();
	}

	unsigned char *DefaultJITMemoryManager::allocateStub(unsigned StubSize,
	unsigned Alignment) {
	CurStubPtr -= StubSize;
	CurStubPtr = (unsigned char*)(((intptr_t)CurStubPtr) &
	~(intptr_t)(Alignment-1));
	if (CurStubPtr < StubBase) {
	// FIXME: allocate a new block
	fprintf(stderr, "JIT ran out of memory for function stubs!\n");
	abort();
	}
	return CurStubPtr;
	}

	sys::MemoryBlock DefaultJITMemoryManager::getNewMemoryBlock(unsigned size) {
	// Allocate a new block close to the last one.
	const sys::MemoryBlock *BOld = Blocks.empty() ? 0 : &Blocks.front();
	std::string ErrMsg;
	sys::MemoryBlock B = sys::Memory::AllocateRWX(size, BOld, &ErrMsg);
	if (B.base() == 0) {
	fprintf(stderr,
	"Allocation failed when allocating new memory in the JIT\n%s\n",
	ErrMsg.c_str());
	abort();
	}
	Blocks.push_back(B);
	return B;
	}


	JITMemoryManager *JITMemoryManager::CreateDefaultMemManager() {
	return new DefaultJITMemoryManager();
	}