vendor/llvm/llvm-r72732

1 files changed, 1095 insertions, 0 deletions

diff --git a/include/llvm/Analysis/LoopInfo.h b/include/llvm/Analysis/LoopInfo.h
new file mode 100644
index 000000000000..fb0b584d41cd
--- /dev/null
+++ b/include/llvm/Analysis/LoopInfo.h
@@ -0,0 +1,1095 @@
+//===- llvm/Analysis/LoopInfo.h - Natural Loop Calculator -------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the LoopInfo class that is used to identify natural loops
+// and determine the loop depth of various nodes of the CFG.  Note that natural
+// loops may actually be several loops that share the same header node.
+//
+// This analysis calculates the nesting structure of loops in a function.  For
+// each natural loop identified, this analysis identifies natural loops
+// contained entirely within the loop and the basic blocks the make up the loop.
+//
+// It can calculate on the fly various bits of information, for example:
+//
+//  * whether there is a preheader for the loop
+//  * the number of back edges to the header
+//  * whether or not a particular block branches out of the loop
+//  * the successor blocks of the loop
+//  * the loop depth
+//  * the trip count
+//  * etc...
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_LOOP_INFO_H
+#define LLVM_ANALYSIS_LOOP_INFO_H
+
+#include "llvm/Pass.h"
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/GraphTraits.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Streams.h"
+#include <algorithm>
+#include <ostream>
+
+namespace llvm {
+
+template<typename T>
+static void RemoveFromVector(std::vector<T*> &V, T *N) {
+  typename std::vector<T*>::iterator I = std::find(V.begin(), V.end(), N);
+  assert(I != V.end() && "N is not in this list!");
+  V.erase(I);
+}
+
+class DominatorTree;
+class LoopInfo;
+template<class N> class LoopInfoBase;
+template<class N> class LoopBase;
+
+typedef LoopBase<BasicBlock> Loop;
+
+//===----------------------------------------------------------------------===//
+/// LoopBase class - Instances of this class are used to represent loops that
+/// are detected in the flow graph
+///
+template<class BlockT>
+class LoopBase {
+  LoopBase<BlockT> *ParentLoop;
+  // SubLoops - Loops contained entirely within this one.
+  std::vector<LoopBase<BlockT>*> SubLoops;
+
+  // Blocks - The list of blocks in this loop.  First entry is the header node.
+  std::vector<BlockT*> Blocks;
+
+  LoopBase(const LoopBase<BlockT> &);                  // DO NOT IMPLEMENT
+  const LoopBase<BlockT>&operator=(const LoopBase<BlockT> &);// DO NOT IMPLEMENT
+public:
+  /// Loop ctor - This creates an empty loop.
+  LoopBase() : ParentLoop(0) {}
+  ~LoopBase() {
+    for (size_t i = 0, e = SubLoops.size(); i != e; ++i)
+      delete SubLoops[i];
+  }
+
+  /// getLoopDepth - Return the nesting level of this loop.  An outer-most
+  /// loop has depth 1, for consistency with loop depth values used for basic
+  /// blocks, where depth 0 is used for blocks not inside any loops.
+  unsigned getLoopDepth() const {
+    unsigned D = 1;
+    for (const LoopBase<BlockT> *CurLoop = ParentLoop; CurLoop;
+         CurLoop = CurLoop->ParentLoop)
+      ++D;
+    return D;
+  }
+  BlockT *getHeader() const { return Blocks.front(); }
+  LoopBase<BlockT> *getParentLoop() const { return ParentLoop; }
+
+  /// contains - Return true if the specified basic block is in this loop
+  ///
+  bool contains(const BlockT *BB) const {
+    return std::find(block_begin(), block_end(), BB) != block_end();
+  }
+
+  /// iterator/begin/end - Return the loops contained entirely within this loop.
+  ///
+  const std::vector<LoopBase<BlockT>*> &getSubLoops() const { return SubLoops; }
+  typedef typename std::vector<LoopBase<BlockT>*>::const_iterator iterator;
+  iterator begin() const { return SubLoops.begin(); }
+  iterator end() const { return SubLoops.end(); }
+  bool empty() const { return SubLoops.empty(); }
+
+  /// getBlocks - Get a list of the basic blocks which make up this loop.
+  ///
+  const std::vector<BlockT*> &getBlocks() const { return Blocks; }
+  typedef typename std::vector<BlockT*>::const_iterator block_iterator;
+  block_iterator block_begin() const { return Blocks.begin(); }
+  block_iterator block_end() const { return Blocks.end(); }
+
+  /// isLoopExit - True if terminator in the block can branch to another block
+  /// that is outside of the current loop.
+  ///
+  bool isLoopExit(const BlockT *BB) const {
+    typedef GraphTraits<BlockT*> BlockTraits;
+    for (typename BlockTraits::ChildIteratorType SI =
+         BlockTraits::child_begin(const_cast<BlockT*>(BB)),
+         SE = BlockTraits::child_end(const_cast<BlockT*>(BB)); SI != SE; ++SI) {
+      if (!contains(*SI))
+        return true;
+    }
+    return false;
+  }
+
+  /// getNumBackEdges - Calculate the number of back edges to the loop header
+  ///
+  unsigned getNumBackEdges() const {
+    unsigned NumBackEdges = 0;
+    BlockT *H = getHeader();
+
+    typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
+    for (typename InvBlockTraits::ChildIteratorType I =
+         InvBlockTraits::child_begin(const_cast<BlockT*>(H)),
+         E = InvBlockTraits::child_end(const_cast<BlockT*>(H)); I != E; ++I)
+      if (contains(*I))
+        ++NumBackEdges;
+
+    return NumBackEdges;
+  }
+
+  /// isLoopInvariant - Return true if the specified value is loop invariant
+  ///
+  inline bool isLoopInvariant(Value *V) const {
+    if (Instruction *I = dyn_cast<Instruction>(V))
+      return !contains(I->getParent());
+    return true;  // All non-instructions are loop invariant
+  }
+
+  //===--------------------------------------------------------------------===//
+  // APIs for simple analysis of the loop.
+  //
+  // Note that all of these methods can fail on general loops (ie, there may not
+  // be a preheader, etc).  For best success, the loop simplification and
+  // induction variable canonicalization pass should be used to normalize loops
+  // for easy analysis.  These methods assume canonical loops.
+
+  /// getExitingBlocks - Return all blocks inside the loop that have successors
+  /// outside of the loop.  These are the blocks _inside of the current loop_
+  /// which branch out.  The returned list is always unique.
+  ///
+  void getExitingBlocks(SmallVectorImpl<BlockT *> &ExitingBlocks) const {
+    // Sort the blocks vector so that we can use binary search to do quick
+    // lookups.
+    SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end());
+    std::sort(LoopBBs.begin(), LoopBBs.end());
+
+    typedef GraphTraits<BlockT*> BlockTraits;
+    for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI)
+      for (typename BlockTraits::ChildIteratorType I =
+          BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI);
+          I != E; ++I)
+        if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I)) {
+          // Not in current loop? It must be an exit block.
+          ExitingBlocks.push_back(*BI);
+          break;
+        }
+  }
+
+  /// getExitingBlock - If getExitingBlocks would return exactly one block,
+  /// return that block. Otherwise return null.
+  BlockT *getExitingBlock() const {
+    SmallVector<BlockT*, 8> ExitingBlocks;
+    getExitingBlocks(ExitingBlocks);
+    if (ExitingBlocks.size() == 1)
+      return ExitingBlocks[0];
+    return 0;
+  }
+
+  /// getExitBlocks - Return all of the successor blocks of this loop.  These
+  /// are the blocks _outside of the current loop_ which are branched to.
+  ///
+  void getExitBlocks(SmallVectorImpl<BlockT*> &ExitBlocks) const {
+    // Sort the blocks vector so that we can use binary search to do quick
+    // lookups.
+    SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end());
+    std::sort(LoopBBs.begin(), LoopBBs.end());
+
+    typedef GraphTraits<BlockT*> BlockTraits;
+    for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI)
+      for (typename BlockTraits::ChildIteratorType I =
+           BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI);
+           I != E; ++I)
+        if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I))
+          // Not in current loop? It must be an exit block.
+          ExitBlocks.push_back(*I);
+  }
+
+  /// getExitBlock - If getExitBlocks would return exactly one block,
+  /// return that block. Otherwise return null.
+  BlockT *getExitBlock() const {
+    SmallVector<BlockT*, 8> ExitBlocks;
+    getExitBlocks(ExitBlocks);
+    if (ExitBlocks.size() == 1)
+      return ExitBlocks[0];
+    return 0;
+  }
+
+  /// getUniqueExitBlocks - Return all unique successor blocks of this loop. 
+  /// These are the blocks _outside of the current loop_ which are branched to.
+  /// This assumes that loop is in canonical form.
+  ///
+  void getUniqueExitBlocks(SmallVectorImpl<BlockT*> &ExitBlocks) const {
+    // Sort the blocks vector so that we can use binary search to do quick
+    // lookups.
+    SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end());
+    std::sort(LoopBBs.begin(), LoopBBs.end());
+
+    std::vector<BlockT*> switchExitBlocks;  
+
+    for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) {
+
+      BlockT *current = *BI;
+      switchExitBlocks.clear();
+
+      typedef GraphTraits<BlockT*> BlockTraits;
+      typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
+      for (typename BlockTraits::ChildIteratorType I =
+           BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI);
+           I != E; ++I) {
+        if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I))
+      // If block is inside the loop then it is not a exit block.
+          continue;
+      
+        typename InvBlockTraits::ChildIteratorType PI =
+                                                InvBlockTraits::child_begin(*I);
+        BlockT *firstPred = *PI;
+
+        // If current basic block is this exit block's first predecessor
+        // then only insert exit block in to the output ExitBlocks vector.
+        // This ensures that same exit block is not inserted twice into
+        // ExitBlocks vector.
+        if (current != firstPred) 
+          continue;
+
+        // If a terminator has more then two successors, for example SwitchInst,
+        // then it is possible that there are multiple edges from current block 
+        // to one exit block. 
+        if (std::distance(BlockTraits::child_begin(current),
+                          BlockTraits::child_end(current)) <= 2) {
+          ExitBlocks.push_back(*I);
+          continue;
+        }
+
+        // In case of multiple edges from current block to exit block, collect
+        // only one edge in ExitBlocks. Use switchExitBlocks to keep track of
+        // duplicate edges.
+        if (std::find(switchExitBlocks.begin(), switchExitBlocks.end(), *I) 
+            == switchExitBlocks.end()) {
+          switchExitBlocks.push_back(*I);
+          ExitBlocks.push_back(*I);
+        }
+      }
+    }
+  }
+
+  /// getLoopPreheader - If there is a preheader for this loop, return it.  A
+  /// loop has a preheader if there is only one edge to the header of the loop
+  /// from outside of the loop.  If this is the case, the block branching to the
+  /// header of the loop is the preheader node.
+  ///
+  /// This method returns null if there is no preheader for the loop.
+  ///
+  BlockT *getLoopPreheader() const {
+    // Keep track of nodes outside the loop branching to the header...
+    BlockT *Out = 0;
+
+    // Loop over the predecessors of the header node...
+    BlockT *Header = getHeader();
+    typedef GraphTraits<BlockT*> BlockTraits;
+    typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
+    for (typename InvBlockTraits::ChildIteratorType PI =
+         InvBlockTraits::child_begin(Header),
+         PE = InvBlockTraits::child_end(Header); PI != PE; ++PI)
+      if (!contains(*PI)) {     // If the block is not in the loop...
+        if (Out && Out != *PI)
+          return 0;             // Multiple predecessors outside the loop
+        Out = *PI;
+      }
+
+    // Make sure there is only one exit out of the preheader.
+    assert(Out && "Header of loop has no predecessors from outside loop?");
+    typename BlockTraits::ChildIteratorType SI = BlockTraits::child_begin(Out);
+    ++SI;
+    if (SI != BlockTraits::child_end(Out))
+      return 0;  // Multiple exits from the block, must not be a preheader.
+
+    // If there is exactly one preheader, return it.  If there was zero, then
+    // Out is still null.
+    return Out;
+  }
+
+  /// getLoopLatch - If there is a single latch block for this loop, return it.
+  /// A latch block is a block that contains a branch back to the header.
+  /// A loop header in normal form has two edges into it: one from a preheader
+  /// and one from a latch block.
+  BlockT *getLoopLatch() const {
+    BlockT *Header = getHeader();
+    typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
+    typename InvBlockTraits::ChildIteratorType PI =
+                                            InvBlockTraits::child_begin(Header);
+    typename InvBlockTraits::ChildIteratorType PE =
+                                              InvBlockTraits::child_end(Header);
+    if (PI == PE) return 0;  // no preds?
+
+    BlockT *Latch = 0;
+    if (contains(*PI))
+      Latch = *PI;
+    ++PI;
+    if (PI == PE) return 0;  // only one pred?
+
+    if (contains(*PI)) {
+      if (Latch) return 0;  // multiple backedges
+      Latch = *PI;
+    }
+    ++PI;
+    if (PI != PE) return 0;  // more than two preds
+
+    return Latch;
+  }
+  
+  /// getCanonicalInductionVariable - Check to see if the loop has a canonical
+  /// induction variable: an integer recurrence that starts at 0 and increments
+  /// by one each time through the loop.  If so, return the phi node that
+  /// corresponds to it.
+  ///
+  /// The IndVarSimplify pass transforms loops to have a canonical induction
+  /// variable.
+  ///
+  inline PHINode *getCanonicalInductionVariable() const {
+    BlockT *H = getHeader();
+
+    BlockT *Incoming = 0, *Backedge = 0;
+    typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
+    typename InvBlockTraits::ChildIteratorType PI =
+                                                 InvBlockTraits::child_begin(H);
+    assert(PI != InvBlockTraits::child_end(H) &&
+           "Loop must have at least one backedge!");
+    Backedge = *PI++;
+    if (PI == InvBlockTraits::child_end(H)) return 0;  // dead loop
+    Incoming = *PI++;
+    if (PI != InvBlockTraits::child_end(H)) return 0;  // multiple backedges?
+
+    if (contains(Incoming)) {
+      if (contains(Backedge))
+        return 0;
+      std::swap(Incoming, Backedge);
+    } else if (!contains(Backedge))
+      return 0;
+
+    // Loop over all of the PHI nodes, looking for a canonical indvar.
+    for (typename BlockT::iterator I = H->begin(); isa<PHINode>(I); ++I) {
+      PHINode *PN = cast<PHINode>(I);
+      if (ConstantInt *CI =
+          dyn_cast<ConstantInt>(PN->getIncomingValueForBlock(Incoming)))
+        if (CI->isNullValue())
+          if (Instruction *Inc =
+              dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
+            if (Inc->getOpcode() == Instruction::Add &&
+                Inc->getOperand(0) == PN)
+              if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
+                if (CI->equalsInt(1))
+                  return PN;
+    }
+    return 0;
+  }
+
+  /// getCanonicalInductionVariableIncrement - Return the LLVM value that holds
+  /// the canonical induction variable value for the "next" iteration of the
+  /// loop.  This always succeeds if getCanonicalInductionVariable succeeds.
+  ///
+  inline Instruction *getCanonicalInductionVariableIncrement() const {
+    if (PHINode *PN = getCanonicalInductionVariable()) {
+      bool P1InLoop = contains(PN->getIncomingBlock(1));
+      return cast<Instruction>(PN->getIncomingValue(P1InLoop));
+    }
+    return 0;
+  }
+
+  /// getTripCount - Return a loop-invariant LLVM value indicating the number of
+  /// times the loop will be executed.  Note that this means that the backedge
+  /// of the loop executes N-1 times.  If the trip-count cannot be determined,
+  /// this returns null.
+  ///
+  /// The IndVarSimplify pass transforms loops to have a form that this
+  /// function easily understands.
+  ///
+  inline Value *getTripCount() const {
+    // Canonical loops will end with a 'cmp ne I, V', where I is the incremented
+    // canonical induction variable and V is the trip count of the loop.
+    Instruction *Inc = getCanonicalInductionVariableIncrement();
+    if (Inc == 0) return 0;
+    PHINode *IV = cast<PHINode>(Inc->getOperand(0));
+
+    BlockT *BackedgeBlock =
+            IV->getIncomingBlock(contains(IV->getIncomingBlock(1)));
+
+    if (BranchInst *BI = dyn_cast<BranchInst>(BackedgeBlock->getTerminator()))
+      if (BI->isConditional()) {
+        if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) {
+          if (ICI->getOperand(0) == Inc) {
+            if (BI->getSuccessor(0) == getHeader()) {
+              if (ICI->getPredicate() == ICmpInst::ICMP_NE)
+                return ICI->getOperand(1);
+            } else if (ICI->getPredicate() == ICmpInst::ICMP_EQ) {
+              return ICI->getOperand(1);
+            }
+          }
+        }
+      }
+
+    return 0;
+  }
+  
+  /// getSmallConstantTripCount - Returns the trip count of this loop as a
+  /// normal unsigned value, if possible. Returns 0 if the trip count is unknown
+  /// of not constant. Will also return 0 if the trip count is very large 
+  /// (>= 2^32)
+  inline unsigned getSmallConstantTripCount() const {
+    Value* TripCount = this->getTripCount();
+    if (TripCount) {
+      if (ConstantInt *TripCountC = dyn_cast<ConstantInt>(TripCount)) {
+        // Guard against huge trip counts.
+        if (TripCountC->getValue().getActiveBits() <= 32) {
+          return (unsigned)TripCountC->getZExtValue();
+        }
+      }
+    }
+    return 0;
+  }
+
+  /// getSmallConstantTripMultiple - Returns the largest constant divisor of the
+  /// trip count of this loop as a normal unsigned value, if possible. This
+  /// means that the actual trip count is always a multiple of the returned
+  /// value (don't forget the trip count could very well be zero as well!).
+  ///
+  /// Returns 1 if the trip count is unknown or not guaranteed to be the
+  /// multiple of a constant (which is also the case if the trip count is simply
+  /// constant, use getSmallConstantTripCount for that case), Will also return 1
+  /// if the trip count is very large (>= 2^32).
+  inline unsigned getSmallConstantTripMultiple() const {
+    Value* TripCount = this->getTripCount();
+    // This will hold the ConstantInt result, if any
+    ConstantInt *Result = NULL;
+    if (TripCount) {
+      // See if the trip count is constant itself
+      Result = dyn_cast<ConstantInt>(TripCount);
+      // if not, see if it is a multiplication
+      if (!Result)
+        if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TripCount)) {
+          switch (BO->getOpcode()) {
+          case BinaryOperator::Mul:
+            Result = dyn_cast<ConstantInt>(BO->getOperand(1));
+            break;
+          default: 
+            break;
+          }
+        }
+    }
+    // Guard against huge trip counts.
+    if (Result && Result->getValue().getActiveBits() <= 32) {
+      return (unsigned)Result->getZExtValue();
+    } else {
+      return 1;
+    }
+  }
+  
+  /// isLCSSAForm - Return true if the Loop is in LCSSA form
+  inline bool isLCSSAForm() const {
+    // Sort the blocks vector so that we can use binary search to do quick
+    // lookups.
+    SmallPtrSet<BlockT*, 16> LoopBBs(block_begin(), block_end());
+
+    for (block_iterator BI = block_begin(), E = block_end(); BI != E; ++BI) {
+      BlockT *BB = *BI;
+      for (typename BlockT::iterator I = BB->begin(), E = BB->end(); I != E;++I)
+        for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
+             ++UI) {
+          BlockT *UserBB = cast<Instruction>(*UI)->getParent();
+          if (PHINode *P = dyn_cast<PHINode>(*UI)) {
+            UserBB = P->getIncomingBlock(UI);
+          }
+
+          // Check the current block, as a fast-path.  Most values are used in
+          // the same block they are defined in.
+          if (UserBB != BB && !LoopBBs.count(UserBB))
+            return false;
+        }
+    }
+
+    return true;
+  }
+
+  //===--------------------------------------------------------------------===//
+  // APIs for updating loop information after changing the CFG
+  //
+
+  /// addBasicBlockToLoop - This method is used by other analyses to update loop
+  /// information.  NewBB is set to be a new member of the current loop.
+  /// Because of this, it is added as a member of all parent loops, and is added
+  /// to the specified LoopInfo object as being in the current basic block.  It
+  /// is not valid to replace the loop header with this method.
+  ///
+  void addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase<BlockT> &LI);
+
+  /// replaceChildLoopWith - This is used when splitting loops up.  It replaces
+  /// the OldChild entry in our children list with NewChild, and updates the
+  /// parent pointer of OldChild to be null and the NewChild to be this loop.
+  /// This updates the loop depth of the new child.
+  void replaceChildLoopWith(LoopBase<BlockT> *OldChild,
+                            LoopBase<BlockT> *NewChild) {
+    assert(OldChild->ParentLoop == this && "This loop is already broken!");
+    assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
+    typename std::vector<LoopBase<BlockT>*>::iterator I =
+                          std::find(SubLoops.begin(), SubLoops.end(), OldChild);
+    assert(I != SubLoops.end() && "OldChild not in loop!");
+    *I = NewChild;
+    OldChild->ParentLoop = 0;
+    NewChild->ParentLoop = this;
+  }
+
+  /// addChildLoop - Add the specified loop to be a child of this loop.  This
+  /// updates the loop depth of the new child.
+  ///
+  void addChildLoop(LoopBase<BlockT> *NewChild) {
+    assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
+    NewChild->ParentLoop = this;
+    SubLoops.push_back(NewChild);
+  }
+
+  /// removeChildLoop - This removes the specified child from being a subloop of
+  /// this loop.  The loop is not deleted, as it will presumably be inserted
+  /// into another loop.
+  LoopBase<BlockT> *removeChildLoop(iterator I) {
+    assert(I != SubLoops.end() && "Cannot remove end iterator!");
+    LoopBase<BlockT> *Child = *I;
+    assert(Child->ParentLoop == this && "Child is not a child of this loop!");
+    SubLoops.erase(SubLoops.begin()+(I-begin()));
+    Child->ParentLoop = 0;
+    return Child;
+  }
+
+  /// addBlockEntry - This adds a basic block directly to the basic block list.
+  /// This should only be used by transformations that create new loops.  Other
+  /// transformations should use addBasicBlockToLoop.
+  void addBlockEntry(BlockT *BB) {
+    Blocks.push_back(BB);
+  }
+
+  /// moveToHeader - This method is used to move BB (which must be part of this
+  /// loop) to be the loop header of the loop (the block that dominates all
+  /// others).
+  void moveToHeader(BlockT *BB) {
+    if (Blocks[0] == BB) return;
+    for (unsigned i = 0; ; ++i) {
+      assert(i != Blocks.size() && "Loop does not contain BB!");
+      if (Blocks[i] == BB) {
+        Blocks[i] = Blocks[0];
+        Blocks[0] = BB;
+        return;
+      }
+    }
+  }
+
+  /// removeBlockFromLoop - This removes the specified basic block from the
+  /// current loop, updating the Blocks as appropriate.  This does not update
+  /// the mapping in the LoopInfo class.
+  void removeBlockFromLoop(BlockT *BB) {
+    RemoveFromVector(Blocks, BB);
+  }
+
+  /// verifyLoop - Verify loop structure
+  void verifyLoop() const {
+#ifndef NDEBUG
+    assert (getHeader() && "Loop header is missing");
+    assert (getLoopPreheader() && "Loop preheader is missing");
+    assert (getLoopLatch() && "Loop latch is missing");
+    for (iterator I = SubLoops.begin(), E = SubLoops.end(); I != E; ++I)
+      (*I)->verifyLoop();
+#endif
+  }
+
+  void print(std::ostream &OS, unsigned Depth = 0) const {
+    OS << std::string(Depth*2, ' ') << "Loop at depth " << getLoopDepth()
+       << " containing: ";
+
+    for (unsigned i = 0; i < getBlocks().size(); ++i) {
+      if (i) OS << ",";
+      BlockT *BB = getBlocks()[i];
+      WriteAsOperand(OS, BB, false);
+      if (BB == getHeader())    OS << "<header>";
+      if (BB == getLoopLatch()) OS << "<latch>";
+      if (isLoopExit(BB))       OS << "<exit>";
+    }
+    OS << "\n";
+
+    for (iterator I = begin(), E = end(); I != E; ++I)
+      (*I)->print(OS, Depth+2);
+  }
+  
+  void print(std::ostream *O, unsigned Depth = 0) const {
+    if (O) print(*O, Depth);
+  }
+  
+  void dump() const {
+    print(cerr);
+  }
+  
+private:
+  friend class LoopInfoBase<BlockT>;
+  explicit LoopBase(BlockT *BB) : ParentLoop(0) {
+    Blocks.push_back(BB);
+  }
+};
+
+
+//===----------------------------------------------------------------------===//
+/// LoopInfo - This class builds and contains all of the top level loop
+/// structures in the specified function.
+///
+
+template<class BlockT>
+class LoopInfoBase {
+  // BBMap - Mapping of basic blocks to the inner most loop they occur in
+  std::map<BlockT*, LoopBase<BlockT>*> BBMap;
+  std::vector<LoopBase<BlockT>*> TopLevelLoops;
+  friend class LoopBase<BlockT>;
+  
+public:
+  LoopInfoBase() { }
+  ~LoopInfoBase() { releaseMemory(); }
+  
+  void releaseMemory() {
+    for (typename std::vector<LoopBase<BlockT>* >::iterator I =
+         TopLevelLoops.begin(), E = TopLevelLoops.end(); I != E; ++I)
+      delete *I;   // Delete all of the loops...
+
+    BBMap.clear();                           // Reset internal state of analysis
+    TopLevelLoops.clear();
+  }
+  
+  /// iterator/begin/end - The interface to the top-level loops in the current
+  /// function.
+  ///
+  typedef typename std::vector<LoopBase<BlockT>*>::const_iterator iterator;
+  iterator begin() const { return TopLevelLoops.begin(); }
+  iterator end() const { return TopLevelLoops.end(); }
+  bool empty() const { return TopLevelLoops.empty(); }
+  
+  /// getLoopFor - Return the inner most loop that BB lives in.  If a basic
+  /// block is in no loop (for example the entry node), null is returned.
+  ///
+  LoopBase<BlockT> *getLoopFor(const BlockT *BB) const {
+    typename std::map<BlockT *, LoopBase<BlockT>*>::const_iterator I=
+      BBMap.find(const_cast<BlockT*>(BB));
+    return I != BBMap.end() ? I->second : 0;
+  }
+  
+  /// operator[] - same as getLoopFor...
+  ///
+  const LoopBase<BlockT> *operator[](const BlockT *BB) const {
+    return getLoopFor(BB);
+  }
+  
+  /// getLoopDepth - Return the loop nesting level of the specified block.  A
+  /// depth of 0 means the block is not inside any loop.
+  ///
+  unsigned getLoopDepth(const BlockT *BB) const {
+    const LoopBase<BlockT> *L = getLoopFor(BB);
+    return L ? L->getLoopDepth() : 0;
+  }
+
+  // isLoopHeader - True if the block is a loop header node
+  bool isLoopHeader(BlockT *BB) const {
+    const LoopBase<BlockT> *L = getLoopFor(BB);
+    return L && L->getHeader() == BB;
+  }
+  
+  /// removeLoop - This removes the specified top-level loop from this loop info
+  /// object.  The loop is not deleted, as it will presumably be inserted into
+  /// another loop.
+  LoopBase<BlockT> *removeLoop(iterator I) {
+    assert(I != end() && "Cannot remove end iterator!");
+    LoopBase<BlockT> *L = *I;
+    assert(L->getParentLoop() == 0 && "Not a top-level loop!");
+    TopLevelLoops.erase(TopLevelLoops.begin() + (I-begin()));
+    return L;
+  }
+  
+  /// changeLoopFor - Change the top-level loop that contains BB to the
+  /// specified loop.  This should be used by transformations that restructure
+  /// the loop hierarchy tree.
+  void changeLoopFor(BlockT *BB, LoopBase<BlockT> *L) {
+    LoopBase<BlockT> *&OldLoop = BBMap[BB];
+    assert(OldLoop && "Block not in a loop yet!");
+    OldLoop = L;
+  }
+  
+  /// changeTopLevelLoop - Replace the specified loop in the top-level loops
+  /// list with the indicated loop.
+  void changeTopLevelLoop(LoopBase<BlockT> *OldLoop,
+                          LoopBase<BlockT> *NewLoop) {
+    typename std::vector<LoopBase<BlockT>*>::iterator I =
+                 std::find(TopLevelLoops.begin(), TopLevelLoops.end(), OldLoop);
+    assert(I != TopLevelLoops.end() && "Old loop not at top level!");
+    *I = NewLoop;
+    assert(NewLoop->ParentLoop == 0 && OldLoop->ParentLoop == 0 &&
+           "Loops already embedded into a subloop!");
+  }
+  
+  /// addTopLevelLoop - This adds the specified loop to the collection of
+  /// top-level loops.
+  void addTopLevelLoop(LoopBase<BlockT> *New) {
+    assert(New->getParentLoop() == 0 && "Loop already in subloop!");
+    TopLevelLoops.push_back(New);
+  }
+  
+  /// removeBlock - This method completely removes BB from all data structures,
+  /// including all of the Loop objects it is nested in and our mapping from
+  /// BasicBlocks to loops.
+  void removeBlock(BlockT *BB) {
+    typename std::map<BlockT *, LoopBase<BlockT>*>::iterator I = BBMap.find(BB);
+    if (I != BBMap.end()) {
+      for (LoopBase<BlockT> *L = I->second; L; L = L->getParentLoop())
+        L->removeBlockFromLoop(BB);
+
+      BBMap.erase(I);
+    }
+  }
+  
+  // Internals
+  
+  static bool isNotAlreadyContainedIn(const LoopBase<BlockT> *SubLoop,
+                                      const LoopBase<BlockT> *ParentLoop) {
+    if (SubLoop == 0) return true;
+    if (SubLoop == ParentLoop) return false;
+    return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
+  }
+  
+  void Calculate(DominatorTreeBase<BlockT> &DT) {
+    BlockT *RootNode = DT.getRootNode()->getBlock();
+
+    for (df_iterator<BlockT*> NI = df_begin(RootNode),
+           NE = df_end(RootNode); NI != NE; ++NI)
+      if (LoopBase<BlockT> *L = ConsiderForLoop(*NI, DT))
+        TopLevelLoops.push_back(L);
+  }
+  
+  LoopBase<BlockT> *ConsiderForLoop(BlockT *BB, DominatorTreeBase<BlockT> &DT) {
+    if (BBMap.find(BB) != BBMap.end()) return 0;// Haven't processed this node?
+
+    std::vector<BlockT *> TodoStack;
+
+    // Scan the predecessors of BB, checking to see if BB dominates any of
+    // them.  This identifies backedges which target this node...
+    typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
+    for (typename InvBlockTraits::ChildIteratorType I =
+         InvBlockTraits::child_begin(BB), E = InvBlockTraits::child_end(BB);
+         I != E; ++I)
+      if (DT.dominates(BB, *I))   // If BB dominates it's predecessor...
+        TodoStack.push_back(*I);
+
+    if (TodoStack.empty()) return 0;  // No backedges to this block...
+
+    // Create a new loop to represent this basic block...
+    LoopBase<BlockT> *L = new LoopBase<BlockT>(BB);
+    BBMap[BB] = L;
+
+    BlockT *EntryBlock = BB->getParent()->begin();
+
+    while (!TodoStack.empty()) {  // Process all the nodes in the loop
+      BlockT *X = TodoStack.back();
+      TodoStack.pop_back();
+
+      if (!L->contains(X) &&         // As of yet unprocessed??
+          DT.dominates(EntryBlock, X)) {   // X is reachable from entry block?
+        // Check to see if this block already belongs to a loop.  If this occurs
+        // then we have a case where a loop that is supposed to be a child of
+        // the current loop was processed before the current loop.  When this
+        // occurs, this child loop gets added to a part of the current loop,
+        // making it a sibling to the current loop.  We have to reparent this
+        // loop.
+        if (LoopBase<BlockT> *SubLoop =
+            const_cast<LoopBase<BlockT>*>(getLoopFor(X)))
+          if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)){
+            // Remove the subloop from it's current parent...
+            assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L);
+            LoopBase<BlockT> *SLP = SubLoop->ParentLoop;  // SubLoopParent
+            typename std::vector<LoopBase<BlockT>*>::iterator I =
+              std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop);
+            assert(I != SLP->SubLoops.end() &&"SubLoop not a child of parent?");
+            SLP->SubLoops.erase(I);   // Remove from parent...
+
+            // Add the subloop to THIS loop...
+            SubLoop->ParentLoop = L;
+            L->SubLoops.push_back(SubLoop);
+          }
+
+        // Normal case, add the block to our loop...
+        L->Blocks.push_back(X);
+        
+        typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
+        
+        // Add all of the predecessors of X to the end of the work stack...
+        TodoStack.insert(TodoStack.end(), InvBlockTraits::child_begin(X),
+                         InvBlockTraits::child_end(X));
+      }
+    }
+
+    // If there are any loops nested within this loop, create them now!
+    for (typename std::vector<BlockT*>::iterator I = L->Blocks.begin(),
+         E = L->Blocks.end(); I != E; ++I)
+      if (LoopBase<BlockT> *NewLoop = ConsiderForLoop(*I, DT)) {
+        L->SubLoops.push_back(NewLoop);
+        NewLoop->ParentLoop = L;
+      }
+
+    // Add the basic blocks that comprise this loop to the BBMap so that this
+    // loop can be found for them.
+    //
+    for (typename std::vector<BlockT*>::iterator I = L->Blocks.begin(),
+           E = L->Blocks.end(); I != E; ++I) {
+      typename std::map<BlockT*, LoopBase<BlockT>*>::iterator BBMI =
+                                                          BBMap.find(*I);
+      if (BBMI == BBMap.end())                       // Not in map yet...
+        BBMap.insert(BBMI, std::make_pair(*I, L));   // Must be at this level
+    }
+
+    // Now that we have a list of all of the child loops of this loop, check to
+    // see if any of them should actually be nested inside of each other.  We
+    // can accidentally pull loops our of their parents, so we must make sure to
+    // organize the loop nests correctly now.
+    {
+      std::map<BlockT*, LoopBase<BlockT>*> ContainingLoops;
+      for (unsigned i = 0; i != L->SubLoops.size(); ++i) {
+        LoopBase<BlockT> *Child = L->SubLoops[i];
+        assert(Child->getParentLoop() == L && "Not proper child loop?");
+
+        if (LoopBase<BlockT> *ContainingLoop =
+                                          ContainingLoops[Child->getHeader()]) {
+          // If there is already a loop which contains this loop, move this loop
+          // into the containing loop.
+          MoveSiblingLoopInto(Child, ContainingLoop);
+          --i;  // The loop got removed from the SubLoops list.
+        } else {
+          // This is currently considered to be a top-level loop.  Check to see
+          // if any of the contained blocks are loop headers for subloops we
+          // have already processed.
+          for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) {
+            LoopBase<BlockT> *&BlockLoop = ContainingLoops[Child->Blocks[b]];
+            if (BlockLoop == 0) {   // Child block not processed yet...
+              BlockLoop = Child;
+            } else if (BlockLoop != Child) {
+              LoopBase<BlockT> *SubLoop = BlockLoop;
+              // Reparent all of the blocks which used to belong to BlockLoops
+              for (unsigned j = 0, e = SubLoop->Blocks.size(); j != e; ++j)
+                ContainingLoops[SubLoop->Blocks[j]] = Child;
+
+              // There is already a loop which contains this block, that means
+              // that we should reparent the loop which the block is currently
+              // considered to belong to to be a child of this loop.
+              MoveSiblingLoopInto(SubLoop, Child);
+              --i;  // We just shrunk the SubLoops list.
+            }
+          }
+        }
+      }
+    }
+
+    return L;
+  }
+  
+  /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside
+  /// of the NewParent Loop, instead of being a sibling of it.
+  void MoveSiblingLoopInto(LoopBase<BlockT> *NewChild,
+                           LoopBase<BlockT> *NewParent) {
+    LoopBase<BlockT> *OldParent = NewChild->getParentLoop();
+    assert(OldParent && OldParent == NewParent->getParentLoop() &&
+           NewChild != NewParent && "Not sibling loops!");
+
+    // Remove NewChild from being a child of OldParent
+    typename std::vector<LoopBase<BlockT>*>::iterator I =
+      std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(),
+                NewChild);
+    assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??");
+    OldParent->SubLoops.erase(I);   // Remove from parent's subloops list
+    NewChild->ParentLoop = 0;
+
+    InsertLoopInto(NewChild, NewParent);
+  }
+  
+  /// InsertLoopInto - This inserts loop L into the specified parent loop.  If
+  /// the parent loop contains a loop which should contain L, the loop gets
+  /// inserted into L instead.
+  void InsertLoopInto(LoopBase<BlockT> *L, LoopBase<BlockT> *Parent) {
+    BlockT *LHeader = L->getHeader();
+    assert(Parent->contains(LHeader) &&
+           "This loop should not be inserted here!");
+
+    // Check to see if it belongs in a child loop...
+    for (unsigned i = 0, e = static_cast<unsigned>(Parent->SubLoops.size());
+         i != e; ++i)
+      if (Parent->SubLoops[i]->contains(LHeader)) {
+        InsertLoopInto(L, Parent->SubLoops[i]);
+        return;
+      }
+
+    // If not, insert it here!
+    Parent->SubLoops.push_back(L);
+    L->ParentLoop = Parent;
+  }
+  
+  // Debugging
+  
+  void print(std::ostream &OS, const Module* ) const {
+    for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
+      TopLevelLoops[i]->print(OS);
+  #if 0
+    for (std::map<BasicBlock*, Loop*>::const_iterator I = BBMap.begin(),
+           E = BBMap.end(); I != E; ++I)
+      OS << "BB '" << I->first->getName() << "' level = "
+         << I->second->getLoopDepth() << "\n";
+  #endif
+  }
+};
+
+class LoopInfo : public FunctionPass {
+  LoopInfoBase<BasicBlock>* LI;
+  friend class LoopBase<BasicBlock>;
+  
+public:
+  static char ID; // Pass identification, replacement for typeid
+
+  LoopInfo() : FunctionPass(&ID) {
+    LI = new LoopInfoBase<BasicBlock>();
+  }
+  
+  ~LoopInfo() { delete LI; }
+
+  LoopInfoBase<BasicBlock>& getBase() { return *LI; }
+
+  /// iterator/begin/end - The interface to the top-level loops in the current
+  /// function.
+  ///
+  typedef std::vector<Loop*>::const_iterator iterator;
+  inline iterator begin() const { return LI->begin(); }
+  inline iterator end() const { return LI->end(); }
+  bool empty() const { return LI->empty(); }
+
+  /// getLoopFor - Return the inner most loop that BB lives in.  If a basic
+  /// block is in no loop (for example the entry node), null is returned.
+  ///
+  inline Loop *getLoopFor(const BasicBlock *BB) const {
+    return LI->getLoopFor(BB);
+  }
+
+  /// operator[] - same as getLoopFor...
+  ///
+  inline const Loop *operator[](const BasicBlock *BB) const {
+    return LI->getLoopFor(BB);
+  }
+
+  /// getLoopDepth - Return the loop nesting level of the specified block.  A
+  /// depth of 0 means the block is not inside any loop.
+  ///
+  inline unsigned getLoopDepth(const BasicBlock *BB) const {
+    return LI->getLoopDepth(BB);
+  }
+
+  // isLoopHeader - True if the block is a loop header node
+  inline bool isLoopHeader(BasicBlock *BB) const {
+    return LI->isLoopHeader(BB);
+  }
+
+  /// runOnFunction - Calculate the natural loop information.
+  ///
+  virtual bool runOnFunction(Function &F);
+
+  virtual void releaseMemory() { LI->releaseMemory(); }
+
+  virtual void print(std::ostream &O, const Module* M = 0) const {
+    if (O) LI->print(O, M);
+  }
+
+  virtual void getAnalysisUsage(AnalysisUsage &AU) const;
+
+  /// removeLoop - This removes the specified top-level loop from this loop info
+  /// object.  The loop is not deleted, as it will presumably be inserted into
+  /// another loop.
+  inline Loop *removeLoop(iterator I) { return LI->removeLoop(I); }
+
+  /// changeLoopFor - Change the top-level loop that contains BB to the
+  /// specified loop.  This should be used by transformations that restructure
+  /// the loop hierarchy tree.
+  inline void changeLoopFor(BasicBlock *BB, Loop *L) {
+    LI->changeLoopFor(BB, L);
+  }
+
+  /// changeTopLevelLoop - Replace the specified loop in the top-level loops
+  /// list with the indicated loop.
+  inline void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) {
+    LI->changeTopLevelLoop(OldLoop, NewLoop);
+  }
+
+  /// addTopLevelLoop - This adds the specified loop to the collection of
+  /// top-level loops.
+  inline void addTopLevelLoop(Loop *New) {
+    LI->addTopLevelLoop(New);
+  }
+
+  /// removeBlock - This method completely removes BB from all data structures,
+  /// including all of the Loop objects it is nested in and our mapping from
+  /// BasicBlocks to loops.
+  void removeBlock(BasicBlock *BB) {
+    LI->removeBlock(BB);
+  }
+};
+
+
+// Allow clients to walk the list of nested loops...
+template <> struct GraphTraits<const Loop*> {
+  typedef const Loop NodeType;
+  typedef std::vector<Loop*>::const_iterator ChildIteratorType;
+
+  static NodeType *getEntryNode(const Loop *L) { return L; }
+  static inline ChildIteratorType child_begin(NodeType *N) {
+    return N->begin();
+  }
+  static inline ChildIteratorType child_end(NodeType *N) {
+    return N->end();
+  }
+};
+
+template <> struct GraphTraits<Loop*> {
+  typedef Loop NodeType;
+  typedef std::vector<Loop*>::const_iterator ChildIteratorType;
+
+  static NodeType *getEntryNode(Loop *L) { return L; }
+  static inline ChildIteratorType child_begin(NodeType *N) {
+    return N->begin();
+  }
+  static inline ChildIteratorType child_end(NodeType *N) {
+    return N->end();
+  }
+};
+
+template<class BlockT>
+void LoopBase<BlockT>::addBasicBlockToLoop(BlockT *NewBB,
+                                           LoopInfoBase<BlockT> &LIB) {
+  assert((Blocks.empty() || LIB[getHeader()] == this) &&
+         "Incorrect LI specified for this loop!");
+  assert(NewBB && "Cannot add a null basic block to the loop!");
+  assert(LIB[NewBB] == 0 && "BasicBlock already in the loop!");
+
+  // Add the loop mapping to the LoopInfo object...
+  LIB.BBMap[NewBB] = this;
+
+  // Add the basic block to this loop and all parent loops...
+  LoopBase<BlockT> *L = this;
+  while (L) {
+    L->Blocks.push_back(NewBB);
+    L = L->getParentLoop();
+  }
+}
+
+} // End llvm namespace
+
+#endif