Make the JIT code emitter properly retry and ask for more memory when it runs

out of memory, and also make the default memory manager allocate more memory
when it runs out.

Also, switch function stubs and global data over to using the BumpPtrAllocator.

This makes it so the JIT no longer mmaps (or the equivalent on Windows) 16 MB
of memory, and instead allocates in 512K slabs.  I suspect this size could go
lower, especially on embedded platforms, now that more slabs can be allocated.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76828 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 319 insertions, 110 deletions

diff --git a/lib/ExecutionEngine/JIT/JITEmitter.cpp b/lib/ExecutionEngine/JIT/JITEmitter.cpp
index ce52273b00..246a0ce76f 100644
--- a/lib/ExecutionEngine/JIT/JITEmitter.cpp
+++ b/lib/ExecutionEngine/JIT/JITEmitter.cpp
@@ -51,6 +51,7 @@ using namespace llvm;
 
 STATISTIC(NumBytes, "Number of bytes of machine code compiled");
 STATISTIC(NumRelos, "Number of relocations applied");
+STATISTIC(NumRetries, "Number of retries with more memory");
 static JIT *TheJIT = 0;
 
 
@@ -425,6 +426,12 @@ namespace {
     // save BufferBegin/BufferEnd/CurBufferPtr here.
     uint8_t *SavedBufferBegin, *SavedBufferEnd, *SavedCurBufferPtr;
 
+    // When reattempting to JIT a function after running out of space, we store
+    // the estimated size of the function we're trying to JIT here, so we can
+    // ask the memory manager for at least this much space.  When we
+    // successfully emit the function, we reset this back to zero.
+    uintptr_t SizeEstimate;
+
     /// Relocations - These are the relocations that the function needs, as
     /// emitted.
     std::vector<MachineRelocation> Relocations;
@@ -496,7 +503,8 @@ namespace {
     DebugLocTuple PrevDLT;
 
   public:
-    JITEmitter(JIT &jit, JITMemoryManager *JMM) : Resolver(jit), CurFn(0) {
+    JITEmitter(JIT &jit, JITMemoryManager *JMM)
+        : SizeEstimate(0), Resolver(jit), CurFn(0) {
       MemMgr = JMM ? JMM : JITMemoryManager::CreateDefaultMemManager();
       if (jit.getJITInfo().needsGOT()) {
         MemMgr->AllocateGOT();
@@ -561,9 +569,14 @@ namespace {
       return MBBLocations[MBB->getNumber()];
     }
 
+    /// retryWithMoreMemory - Log a retry and deallocate all memory for the
+    /// given function.  Increase the minimum allocation size so that we get
+    /// more memory next time.
+    void retryWithMoreMemory(MachineFunction &F);
+
     /// deallocateMemForFunction - Deallocate all memory for the specified
     /// function body.
-    void deallocateMemForFunction(Function *F);
+    void deallocateMemForFunction(const Function *F);
 
     /// AddStubToCurrentFunction - Mark the current function being JIT'd as
     /// using the stub at the specified address. Allows
@@ -925,6 +938,9 @@ void JITEmitter::startFunction(MachineFunction &F) {
     // previously allocated.
     ActualSize += GetSizeOfGlobalsInBytes(F);
     DOUT << "JIT: ActualSize after globals " << ActualSize << "\n";
+  } else if (SizeEstimate > 0) {
+    // SizeEstimate will be non-zero on reallocation attempts.
+    ActualSize = SizeEstimate;
   }
 
   BufferBegin = CurBufferPtr = MemMgr->startFunctionBody(F.getFunction(),
@@ -949,12 +965,15 @@ void JITEmitter::startFunction(MachineFunction &F) {
 
 bool JITEmitter::finishFunction(MachineFunction &F) {
   if (CurBufferPtr == BufferEnd) {
-    // FIXME: Allocate more space, then try again.
-    llvm_report_error("JIT: Ran out of space for generated machine code!");
+    // We must call endFunctionBody before retrying, because
+    // deallocateMemForFunction requires it.
+    MemMgr->endFunctionBody(F.getFunction(), BufferBegin, CurBufferPtr);
+    retryWithMoreMemory(F);
+    return true;
   }
-  
+
   emitJumpTableInfo(F.getJumpTableInfo());
-  
+
   // FnStart is the start of the text, not the start of the constant pool and
   // other per-function data.
   uint8_t *FnStart =
@@ -1045,8 +1064,12 @@ bool JITEmitter::finishFunction(MachineFunction &F) {
   MemMgr->endFunctionBody(F.getFunction(), BufferBegin, CurBufferPtr);
 
   if (CurBufferPtr == BufferEnd) {
-    // FIXME: Allocate more space, then try again.
-    llvm_report_error("JIT: Ran out of space for generated machine code!");
+    retryWithMoreMemory(F);
+    return true;
+  } else {
+    // Now that we've succeeded in emitting the function, reset the
+    // SizeEstimate back down to zero.
+    SizeEstimate = 0;
   }
 
   BufferBegin = CurBufferPtr = 0;
@@ -1131,9 +1154,19 @@ bool JITEmitter::finishFunction(MachineFunction &F) {
   return false;
 }
 
+void JITEmitter::retryWithMoreMemory(MachineFunction &F) {
+  DOUT << "JIT: Ran out of space for native code.  Reattempting.\n";
+  Relocations.clear();  // Clear the old relocations or we'll reapply them.
+  ConstPoolAddresses.clear();
+  ++NumRetries;
+  deallocateMemForFunction(F.getFunction());
+  // Try again with at least twice as much free space.
+  SizeEstimate = (uintptr_t)(2 * (BufferEnd - BufferBegin));
+}
+
 /// deallocateMemForFunction - Deallocate all memory for the specified
 /// function body.  Also drop any references the function has to stubs.
-void JITEmitter::deallocateMemForFunction(Function *F) {
+void JITEmitter::deallocateMemForFunction(const Function *F) {
   MemMgr->deallocateMemForFunction(F);
 
   // If the function did not reference any stubs, return.
diff --git a/lib/ExecutionEngine/JIT/JITMemoryManager.cpp b/lib/ExecutionEngine/JIT/JITMemoryManager.cpp
index 253c001ba3..2d64fcfa49 100644
--- a/lib/ExecutionEngine/JIT/JITMemoryManager.cpp
+++ b/lib/ExecutionEngine/JIT/JITMemoryManager.cpp
@@ -11,10 +11,16 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/GlobalValue.h"
+#define DEBUG_TYPE "jit"
 #include "llvm/ExecutionEngine/JITMemoryManager.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/GlobalValue.h"
+#include "llvm/Support/Allocator.h"
 #include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
 #include "llvm/System/Memory.h"
 #include <map>
 #include <vector>
@@ -25,6 +31,7 @@
 #include <cstring>
 using namespace llvm;
 
+STATISTIC(NumSlabs, "Number of slabs of memory allocated by the JIT");
 
 JITMemoryManager::~JITMemoryManager() {}
 
@@ -141,7 +148,7 @@ FreeRangeHeader *FreeRangeHeader::AllocateBlock() {
 /// FreeRangeHeader to allocate from.
 FreeRangeHeader *MemoryRangeHeader::FreeBlock(FreeRangeHeader *FreeList) {
   MemoryRangeHeader *FollowingBlock = &getBlockAfter();
-  assert(ThisAllocated && "This block is already allocated!");
+  assert(ThisAllocated && "This block is already free!");
   assert(FollowingBlock->PrevAllocated && "Flags out of sync!");
   
   FreeRangeHeader *FreeListToReturn = FreeList;
@@ -244,70 +251,157 @@ TrimAllocationToSize(FreeRangeHeader *FreeList, uint64_t NewSize) {
 // Memory Block Implementation.
 //===----------------------------------------------------------------------===//
 
-namespace {  
+namespace {
+
+  class DefaultJITMemoryManager;
+
+  class JITSlabAllocator : public SlabAllocator {
+    DefaultJITMemoryManager &JMM;
+  public:
+    JITSlabAllocator(DefaultJITMemoryManager &jmm) : JMM(jmm) { }
+    virtual ~JITSlabAllocator() { }
+    virtual MemSlab *Allocate(size_t Size);
+    virtual void Deallocate(MemSlab *Slab);
+  };
+
   /// 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 {
-    bool PoisonMemory;  // Whether to poison freed memory.
+  class DefaultJITMemoryManager : public JITMemoryManager {
+
+    // Whether to poison freed memory.
+    bool PoisonMemory;
+
+    /// LastSlab - This points to the last slab allocated and is used as the
+    /// NearBlock parameter to AllocateRWX so that we can attempt to lay out all
+    /// stubs, data, and code contiguously in memory.  In general, however, this
+    /// is not possible because the NearBlock parameter is ignored on Windows
+    /// platforms and even on Unix it works on a best-effort pasis.
+    sys::MemoryBlock LastSlab;
+
+    // Memory slabs allocated by the JIT.  We refer to them as slabs so we don't
+    // confuse them with the blocks of memory descibed above.
+    std::vector<sys::MemoryBlock> CodeSlabs;
+    JITSlabAllocator BumpSlabAllocator;
+    BumpPtrAllocator StubAllocator;
+    BumpPtrAllocator DataAllocator;
+
+    // Circular list of free blocks.
+    FreeRangeHeader *FreeMemoryList;
 
-    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;
-    
-    uint8_t *CurStubPtr, *StubBase;
-    uint8_t *CurGlobalPtr, *GlobalEnd;
+
     uint8_t *GOTBase;     // Target Specific reserved memory
     void *DlsymTable;     // Stub external symbol information
 
-    // Centralize memory block allocation.
-    sys::MemoryBlock getNewMemoryBlock(unsigned size);
-    
     std::map<const Function*, MemoryRangeHeader*> FunctionBlocks;
     std::map<const Function*, MemoryRangeHeader*> TableBlocks;
   public:
     DefaultJITMemoryManager();
     ~DefaultJITMemoryManager();
 
+    /// allocateNewSlab - Allocates a new MemoryBlock and remembers it as the
+    /// last slab it allocated, so that subsequent allocations follow it.
+    sys::MemoryBlock allocateNewSlab(size_t size);
+
+    /// DefaultCodeSlabSize - When we have to go map more memory, we allocate at
+    /// least this much unless more is requested.
+    static const size_t DefaultCodeSlabSize;
+
+    /// DefaultSlabSize - Allocate data into slabs of this size unless we get
+    /// an allocation above SizeThreshold.
+    static const size_t DefaultSlabSize;
+
+    /// DefaultSizeThreshold - For any allocation larger than this threshold, we
+    /// should allocate a separate slab.
+    static const size_t DefaultSizeThreshold;
+
     void AllocateGOT();
     void SetDlsymTable(void *);
-    
-    uint8_t *allocateStub(const GlobalValue* F, unsigned StubSize,
-                          unsigned Alignment);
-    
+
+    // Testing methods.
+    virtual bool CheckInvariants(std::string &ErrorStr);
+    size_t GetDefaultCodeSlabSize() { return DefaultCodeSlabSize; }
+    size_t GetDefaultDataSlabSize() { return DefaultSlabSize; }
+    size_t GetDefaultStubSlabSize() { return DefaultSlabSize; }
+    unsigned GetNumCodeSlabs() { return CodeSlabs.size(); }
+    unsigned GetNumDataSlabs() { return DataAllocator.GetNumSlabs(); }
+    unsigned GetNumStubSlabs() { return StubAllocator.GetNumSlabs(); }
+
     /// startFunctionBody - When a function starts, allocate a block of free
     /// executable memory, returning a pointer to it and its actual size.
     uint8_t *startFunctionBody(const Function *F, uintptr_t &ActualSize) {
-      
+
       FreeRangeHeader* candidateBlock = FreeMemoryList;
       FreeRangeHeader* head = FreeMemoryList;
       FreeRangeHeader* iter = head->Next;
 
       uintptr_t largest = candidateBlock->BlockSize;
-      
+
       // Search for the largest free block
       while (iter != head) {
-          if (iter->BlockSize > largest) {
-              largest = iter->BlockSize;
-              candidateBlock = iter;
-          }
-          iter = iter->Next;
+        if (iter->BlockSize > largest) {
+          largest = iter->BlockSize;
+          candidateBlock = iter;
+        }
+        iter = iter->Next;
       }
-      
+
+      // If this block isn't big enough for the allocation desired, allocate
+      // another block of memory and add it to the free list.
+      if (largest - sizeof(MemoryRangeHeader) < ActualSize) {
+        DOUT << "JIT: Allocating another slab of memory for function.";
+        candidateBlock = allocateNewCodeSlab((size_t)ActualSize);
+      }
+
       // Select this candidate block for allocation
       CurBlock = candidateBlock;
 
       // Allocate the entire memory block.
       FreeMemoryList = candidateBlock->AllocateBlock();
-      ActualSize = CurBlock->BlockSize-sizeof(MemoryRangeHeader);
-      return (uint8_t *)(CurBlock+1);
+      ActualSize = CurBlock->BlockSize - sizeof(MemoryRangeHeader);
+      return (uint8_t *)(CurBlock + 1);
     }
-    
+
+    /// allocateNewCodeSlab - Helper method to allocate a new slab of code
+    /// memory from the OS and add it to the free list.  Returns the new
+    /// FreeRangeHeader at the base of the slab.
+    FreeRangeHeader *allocateNewCodeSlab(size_t MinSize) {
+      // If the user needs at least MinSize free memory, then we account for
+      // two MemoryRangeHeaders: the one in the user's block, and the one at the
+      // end of the slab.
+      size_t PaddedMin = MinSize + 2 * sizeof(MemoryRangeHeader);
+      size_t SlabSize = std::max(DefaultCodeSlabSize, PaddedMin);
+      sys::MemoryBlock B = allocateNewSlab(SlabSize);
+      CodeSlabs.push_back(B);
+      char *MemBase = (char*)(B.base());
+
+      // Put a tiny allocated block at the end of the memory chunk, so when
+      // FreeBlock calls getBlockAfter it doesn't fall off the end.
+      MemoryRangeHeader *EndBlock =
+          (MemoryRangeHeader*)(MemBase + B.size()) - 1;
+      EndBlock->ThisAllocated = 1;
+      EndBlock->PrevAllocated = 0;
+      EndBlock->BlockSize = sizeof(MemoryRangeHeader);
+
+      // Start out with a vast new block of free memory.
+      FreeRangeHeader *NewBlock = (FreeRangeHeader*)MemBase;
+      NewBlock->ThisAllocated = 0;
+      // Make sure getFreeBlockBefore doesn't look into unmapped memory.
+      NewBlock->PrevAllocated = 1;
+      NewBlock->BlockSize = (uintptr_t)EndBlock - (uintptr_t)NewBlock;
+      NewBlock->SetEndOfBlockSizeMarker();
+      NewBlock->AddToFreeList(FreeMemoryList);
+
+      assert(NewBlock->BlockSize - sizeof(MemoryRangeHeader) >= MinSize &&
+             "The block was too small!");
+      return NewBlock;
+    }
+
     /// endFunctionBody - The function F is now allocated, and takes the memory
     /// in the range [FunctionStart,FunctionEnd).
     void endFunctionBody(const Function *F, uint8_t *FunctionStart,
@@ -323,7 +417,8 @@ namespace {
       FreeMemoryList =CurBlock->TrimAllocationToSize(FreeMemoryList, BlockSize);
     }
 
-    /// allocateSpace - Allocate a memory block of the given size.
+    /// allocateSpace - Allocate a memory block of the given size.  This method
+    /// cannot be called between calls to startFunctionBody and endFunctionBody.
     uint8_t *allocateSpace(intptr_t Size, unsigned Alignment) {
       CurBlock = FreeMemoryList;
       FreeMemoryList = FreeMemoryList->AllocateBlock();
@@ -340,27 +435,15 @@ namespace {
       return result;
     }
 
-    /// allocateGlobal - Allocate memory for a global.  Unlike allocateSpace,
-    /// this method does not touch the current block and can be called at any
-    /// time.
-    uint8_t *allocateGlobal(uintptr_t Size, unsigned Alignment) {
-      uint8_t *Result = CurGlobalPtr;
-
-      // Align the pointer.
-      if (Alignment == 0) Alignment = 1;
-      Result = (uint8_t*)(((uintptr_t)Result + Alignment-1) &
-                          ~(uintptr_t)(Alignment-1));
-
-      // Move the current global pointer forward.
-      CurGlobalPtr += Result - CurGlobalPtr + Size;
-
-      // Check for overflow.
-      if (CurGlobalPtr > GlobalEnd) {
-        // FIXME: Allocate more memory.
-        llvm_report_error("JIT ran out of memory for globals!");
-      }
+    /// allocateStub - Allocate memory for a function stub.
+    uint8_t *allocateStub(const GlobalValue* F, unsigned StubSize,
+                          unsigned Alignment) {
+      return (uint8_t*)StubAllocator.Allocate(StubSize, Alignment);
+    }
 
-      return Result;
+    /// allocateGlobal - Allocate memory for a global.
+    uint8_t *allocateGlobal(uintptr_t Size, unsigned Alignment) {
+      return (uint8_t*)DataAllocator.Allocate(Size, Alignment);
     }
 
     /// startExceptionTable - Use startFunctionBody to allocate memory for the 
@@ -437,15 +520,15 @@ namespace {
     /// the code pages may need permissions changed.
     void setMemoryWritable(void)
     {
-      for (unsigned i = 0, e = Blocks.size(); i != e; ++i)
-        sys::Memory::setWritable(Blocks[i]);
+      for (unsigned i = 0, e = CodeSlabs.size(); i != e; ++i)
+        sys::Memory::setWritable(CodeSlabs[i]);
     }
     /// setMemoryExecutable - When code generation is done and we're ready to
     /// start execution, the code pages may need permissions changed.
     void setMemoryExecutable(void)
     {
-      for (unsigned i = 0, e = Blocks.size(); i != e; ++i)
-        sys::Memory::setExecutable(Blocks[i]);
+      for (unsigned i = 0, e = CodeSlabs.size(); i != e; ++i)
+        sys::Memory::setExecutable(CodeSlabs[i]);
     }
 
     /// setPoisonMemory - Controls whether we write garbage over freed memory.
@@ -456,28 +539,35 @@ namespace {
   };
 }
 
-DefaultJITMemoryManager::DefaultJITMemoryManager() {
+MemSlab *JITSlabAllocator::Allocate(size_t Size) {
+  sys::MemoryBlock B = JMM.allocateNewSlab(Size);
+  MemSlab *Slab = (MemSlab*)B.base();
+  Slab->Size = B.size();
+  Slab->NextPtr = 0;
+  return Slab;
+}
+
+void JITSlabAllocator::Deallocate(MemSlab *Slab) {
+  sys::MemoryBlock B(Slab, Slab->Size);
+  sys::Memory::ReleaseRWX(B);
+}
+
+DefaultJITMemoryManager::DefaultJITMemoryManager()
+  : LastSlab(0, 0),
+    BumpSlabAllocator(*this),
+    StubAllocator(DefaultSlabSize, DefaultSizeThreshold, BumpSlabAllocator),
+    DataAllocator(DefaultSlabSize, DefaultSizeThreshold, BumpSlabAllocator) {
+
 #ifdef NDEBUG
-  PoisonMemory = true;
-#else
   PoisonMemory = false;
-#endif
-
-  // Allocate a 16M block of memory for functions.
-#if defined(__APPLE__) && defined(__arm__)
-  sys::MemoryBlock MemBlock = getNewMemoryBlock(4 << 20);
 #else
-  sys::MemoryBlock MemBlock = getNewMemoryBlock(16 << 20);
+  PoisonMemory = true;
 #endif
 
-  uint8_t *MemBase = static_cast<uint8_t*>(MemBlock.base());
-
-  // Allocate stubs backwards to the base, globals forward from the stubs, and
-  // functions forward after globals.
-  StubBase   = MemBase;
-  CurStubPtr = MemBase + 512*1024; // Use 512k for stubs, working backwards.
-  CurGlobalPtr = CurStubPtr;       // Use 2M for globals, working forwards.
-  GlobalEnd = CurGlobalPtr + 2*1024*1024;
+  // Allocate space for code.
+  sys::MemoryBlock MemBlock = allocateNewSlab(DefaultCodeSlabSize);
+  CodeSlabs.push_back(MemBlock);
+  uint8_t *MemBase = (uint8_t*)MemBlock.base();
 
   // We set up the memory chunk with 4 mem regions, like this:
   //  [ START
@@ -494,7 +584,7 @@ DefaultJITMemoryManager::DefaultJITMemoryManager() {
   MemoryRangeHeader *Mem3 = (MemoryRangeHeader*)(MemBase+MemBlock.size())-1;
   Mem3->ThisAllocated = 1;
   Mem3->PrevAllocated = 0;
-  Mem3->BlockSize     = 0;
+  Mem3->BlockSize     = sizeof(MemoryRangeHeader);
   
   /// Add a tiny free region so that the free list always has one entry.
   FreeRangeHeader *Mem2 = 
@@ -510,12 +600,12 @@ DefaultJITMemoryManager::DefaultJITMemoryManager() {
   MemoryRangeHeader *Mem1 = (MemoryRangeHeader*)Mem2-1;
   Mem1->ThisAllocated = 1;
   Mem1->PrevAllocated = 0;
-  Mem1->BlockSize     = (char*)Mem2 - (char*)Mem1;
+  Mem1->BlockSize     = sizeof(MemoryRangeHeader);
   
   // 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*)GlobalEnd;
+  FreeRangeHeader *Mem0 = (FreeRangeHeader*)MemBase;
   Mem0->ThisAllocated = 0;
   Mem0->PrevAllocated = 1;
   Mem0->BlockSize = (char*)Mem1-(char*)Mem0;
@@ -540,40 +630,124 @@ void DefaultJITMemoryManager::SetDlsymTable(void *ptr) {
 }
 
 DefaultJITMemoryManager::~DefaultJITMemoryManager() {
-  for (unsigned i = 0, e = Blocks.size(); i != e; ++i)
-    sys::Memory::ReleaseRWX(Blocks[i]);
-  
-  delete[] GOTBase;
-  Blocks.clear();
-}
+  for (unsigned i = 0, e = CodeSlabs.size(); i != e; ++i)
+    sys::Memory::ReleaseRWX(CodeSlabs[i]);
 
-uint8_t *DefaultJITMemoryManager::allocateStub(const GlobalValue* F,
-                                                     unsigned StubSize,
-                                                     unsigned Alignment) {
-  CurStubPtr -= StubSize;
-  CurStubPtr = (uint8_t*)(((intptr_t)CurStubPtr) &
-                          ~(intptr_t)(Alignment-1));
-  if (CurStubPtr < StubBase) {
-    // FIXME: allocate a new block
-    llvm_report_error("JIT ran out of memory for function stubs!");
-  }
-  return CurStubPtr;
+  delete[] GOTBase;
 }
 
-sys::MemoryBlock DefaultJITMemoryManager::getNewMemoryBlock(unsigned size) {
+sys::MemoryBlock DefaultJITMemoryManager::allocateNewSlab(size_t size) {
   // Allocate a new block close to the last one.
-  const sys::MemoryBlock *BOld = Blocks.empty() ? 0 : &Blocks.back();
   std::string ErrMsg;
-  sys::MemoryBlock B = sys::Memory::AllocateRWX(size, BOld, &ErrMsg);
+  sys::MemoryBlock *LastSlabPtr = LastSlab.base() ? &LastSlab : 0;
+  sys::MemoryBlock B = sys::Memory::AllocateRWX(size, LastSlabPtr, &ErrMsg);
   if (B.base() == 0) {
     llvm_report_error("Allocation failed when allocating new memory in the"
                       " JIT\n" + ErrMsg);
   }
-  Blocks.push_back(B);
+  LastSlab = B;
+  ++NumSlabs;
   return B;
 }
 
+/// CheckInvariants - For testing only.  Return "" if all internal invariants
+/// are preserved, and a helpful error message otherwise.  For free and
+/// allocated blocks, make sure that adding BlockSize gives a valid block.
+/// For free blocks, make sure they're in the free list and that their end of
+/// block size marker is correct.  This function should return an error before
+/// accessing bad memory.  This function is defined here instead of in
+/// JITMemoryManagerTest.cpp so that we don't have to expose all of the
+/// implementation details of DefaultJITMemoryManager.
+bool DefaultJITMemoryManager::CheckInvariants(std::string &ErrorStr) {
+  raw_string_ostream Err(ErrorStr);
+
+  // Construct a the set of FreeRangeHeader pointers so we can query it
+  // efficiently.
+  llvm::SmallPtrSet<MemoryRangeHeader*, 16> FreeHdrSet;
+  FreeRangeHeader* FreeHead = FreeMemoryList;
+  FreeRangeHeader* FreeRange = FreeHead;
+
+  do {
+    // Check that the free range pointer is in the blocks we've allocated.
+    bool Found = false;
+    for (std::vector<sys::MemoryBlock>::iterator I = CodeSlabs.begin(),
+         E = CodeSlabs.end(); I != E && !Found; ++I) {
+      char *Start = (char*)I->base();
+      char *End = Start + I->size();
+      Found = (Start <= (char*)FreeRange && (char*)FreeRange < End);
+    }
+    if (!Found) {
+      Err << "Corrupt free list; points to " << FreeRange;
+      return false;
+    }
+
+    if (FreeRange->Next->Prev != FreeRange) {
+      Err << "Next and Prev pointers do not match.";
+      return false;
+    }
+
+    // Otherwise, add it to the set.
+    FreeHdrSet.insert(FreeRange);
+    FreeRange = FreeRange->Next;
+  } while (FreeRange != FreeHead);
+
+  // Go over each block, and look at each MemoryRangeHeader.
+  for (std::vector<sys::MemoryBlock>::iterator I = CodeSlabs.begin(),
+       E = CodeSlabs.end(); I != E; ++I) {
+    char *Start = (char*)I->base();
+    char *End = Start + I->size();
+
+    // Check each memory range.
+    for (MemoryRangeHeader *Hdr = (MemoryRangeHeader*)Start, *LastHdr = NULL;
+         Start <= (char*)Hdr && (char*)Hdr < End;
+         Hdr = &Hdr->getBlockAfter()) {
+      if (Hdr->ThisAllocated == 0) {
+        // Check that this range is in the free list.
+        if (!FreeHdrSet.count(Hdr)) {
+          Err << "Found free header at " << Hdr << " that is not in free list.";
+          return false;
+        }
+
+        // Now make sure the size marker at the end of the block is correct.
+        uintptr_t *Marker = ((uintptr_t*)&Hdr->getBlockAfter()) - 1;
+        if (!(Start <= (char*)Marker && (char*)Marker < End)) {
+          Err << "Block size in header points out of current MemoryBlock.";
+          return false;
+        }
+        if (Hdr->BlockSize != *Marker) {
+          Err << "End of block size marker (" << *Marker << ") "
+              << "and BlockSize (" << Hdr->BlockSize << ") don't match.";
+          return false;
+        }
+      }
+
+      if (LastHdr && LastHdr->ThisAllocated != Hdr->PrevAllocated) {
+        Err << "Hdr->PrevAllocated (" << Hdr->PrevAllocated << ") != "
+            << "LastHdr->ThisAllocated (" << LastHdr->ThisAllocated << ")";
+        return false;
+      } else if (!LastHdr && !Hdr->PrevAllocated) {
+        Err << "The first header should have PrevAllocated true.";
+        return false;
+      }
+
+      // Remember the last header.
+      LastHdr = Hdr;
+    }
+  }
+
+  // All invariants are preserved.
+  return true;
+}
 
 JITMemoryManager *JITMemoryManager::CreateDefaultMemManager() {
   return new DefaultJITMemoryManager();
 }
+
+// Allocate memory for code in 512K slabs.
+const size_t DefaultJITMemoryManager::DefaultCodeSlabSize = 512 * 1024;
+
+// Allocate globals and stubs in slabs of 64K.  (probably 16 pages)
+const size_t DefaultJITMemoryManager::DefaultSlabSize = 64 * 1024;
+
+// Waste at most 16K at the end of each bump slab.  (probably 4 pages)
+const size_t DefaultJITMemoryManager::DefaultSizeThreshold = 16 * 1024;
diff --git a/lib/System/Unix/Memory.inc b/lib/System/Unix/Memory.inc
index b7a70135bc..a80f56fbc1 100644
--- a/lib/System/Unix/Memory.inc
+++ b/lib/System/Unix/Memory.inc
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "Unix.h"
+#include "llvm/Support/DataTypes.h"
 #include "llvm/System/Process.h"
 
 #ifdef HAVE_SYS_MMAN_H
@@ -28,12 +29,12 @@
 /// is very OS specific.
 ///
 llvm::sys::MemoryBlock 
-llvm::sys::Memory::AllocateRWX(unsigned NumBytes, const MemoryBlock* NearBlock,
+llvm::sys::Memory::AllocateRWX(size_t NumBytes, const MemoryBlock* NearBlock,
                                std::string *ErrMsg) {
   if (NumBytes == 0) return MemoryBlock();
 
-  unsigned pageSize = Process::GetPageSize();
-  unsigned NumPages = (NumBytes+pageSize-1)/pageSize;
+  size_t pageSize = Process::GetPageSize();
+  size_t NumPages = (NumBytes+pageSize-1)/pageSize;
 
   int fd = -1;
 #ifdef NEED_DEV_ZERO_FOR_MMAP
diff --git a/lib/System/Win32/Memory.inc b/lib/System/Win32/Memory.inc
index 5e5cf7a676..7611ecdb92 100644
--- a/lib/System/Win32/Memory.inc
+++ b/lib/System/Win32/Memory.inc
@@ -13,6 +13,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "Win32.h"
+#include "llvm/Support/DataTypes.h"
 #include "llvm/System/Process.h"
 
 namespace llvm {
@@ -23,13 +24,13 @@ using namespace sys;
 //===          and must not be UNIX code
 //===----------------------------------------------------------------------===//
 
-MemoryBlock Memory::AllocateRWX(unsigned NumBytes,
+MemoryBlock Memory::AllocateRWX(size_t NumBytes,
                                 const MemoryBlock *NearBlock,
                                 std::string *ErrMsg) {
   if (NumBytes == 0) return MemoryBlock();
 
-  static const long pageSize = Process::GetPageSize();
-  unsigned NumPages = (NumBytes+pageSize-1)/pageSize;
+  static const size_t pageSize = Process::GetPageSize();
+  size_t NumPages = (NumBytes+pageSize-1)/pageSize;
 
   //FIXME: support NearBlock if ever needed on Win64.