lib/Transforms/Scalar/LoopRotation.cpp - platform/external/llvm - Gitiles

 //===- LoopRotation.cpp - Loop Rotation Pass ------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements Loop Rotation Pass.
 //
 //===----------------------------------------------------------------------===//

 #define DEBUG_TYPE "loop-rotate"

 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Function.h"
 #include "llvm/Instructions.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/Dominators.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/SmallVector.h"

 using namespace llvm;

 #define MAX_HEADER_SIZE 16

 STATISTIC(NumRotated, "Number of loops rotated");
 namespace {

   class VISIBILITY_HIDDEN RenameData {
   public:
     RenameData(Instruction *O, Value *P, Instruction *H)
       : Original(O), PreHeader(P), Header(H) { }
   public:
     Instruction *Original; // Original instruction
     Value *PreHeader; // Original pre-header replacement
     Instruction *Header; // New header replacement
   };

   class VISIBILITY_HIDDEN LoopRotate : public LoopPass {

   public:
     static char ID; // Pass ID, replacement for typeid
     LoopRotate() : LoopPass(&ID) {}

     // Rotate Loop L as many times as possible. Return true if
     // loop is rotated at least once.
     bool runOnLoop(Loop *L, LPPassManager &LPM);

     // LCSSA form makes instruction renaming easier.
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
       AU.addRequiredID(LoopSimplifyID);
       AU.addPreservedID(LoopSimplifyID);
       AU.addRequiredID(LCSSAID);
       AU.addPreservedID(LCSSAID);
       AU.addPreserved<ScalarEvolution>();
       AU.addPreserved<LoopInfo>();
       AU.addPreserved<DominatorTree>();
       AU.addPreserved<DominanceFrontier>();
     }

     // Helper functions

     /// Do actual work
     bool rotateLoop(Loop *L, LPPassManager &LPM);

     /// Initialize local data
     void initialize();

     /// Make sure all Exit block PHINodes have required incoming values.
     /// If incoming value is constant or defined outside the loop then
     /// PHINode may not have an entry for original pre-header.
     void  updateExitBlock();

     /// Return true if this instruction is used outside original header.
     bool usedOutsideOriginalHeader(Instruction *In);

     /// Find Replacement information for instruction. Return NULL if it is
     /// not available.
     const RenameData *findReplacementData(Instruction *I);

     /// After loop rotation, loop pre-header has multiple sucessors.
     /// Insert one forwarding basic block to ensure that loop pre-header
     /// has only one successor.
     void preserveCanonicalLoopForm(LPPassManager &LPM);

   private:

     Loop *L;
     BasicBlock *OrigHeader;
     BasicBlock *OrigPreHeader;
     BasicBlock *OrigLatch;
     BasicBlock *NewHeader;
     BasicBlock *Exit;
     LPPassManager *LPM_Ptr;
     SmallVector<RenameData, MAX_HEADER_SIZE> LoopHeaderInfo;
   };
 }

 char LoopRotate::ID = 0;
 static RegisterPass<LoopRotate> X("loop-rotate", "Rotate Loops");

 Pass *llvm::createLoopRotatePass() { return new LoopRotate(); }

 /// Rotate Loop L as many times as possible. Return true if
 /// loop is rotated at least once.
 bool LoopRotate::runOnLoop(Loop *Lp, LPPassManager &LPM) {

   bool RotatedOneLoop = false;
   initialize();
   LPM_Ptr = &LPM;

   // One loop can be rotated multiple times.
   while (rotateLoop(Lp,LPM)) {
     RotatedOneLoop = true;
     initialize();
   }

   return RotatedOneLoop;
 }

 /// Rotate loop LP. Return true if the loop is rotated.
 bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) {

   L = Lp;

   OrigHeader =  L->getHeader();
   OrigPreHeader = L->getLoopPreheader();
   OrigLatch = L->getLoopLatch();

   // If loop has only one block then there is not much to rotate.
   if (L->getBlocks().size() == 1)
     return false;

   assert (OrigHeader && OrigLatch && OrigPreHeader &&
           "Loop is not in canonical form");

   // If loop header is not one of the loop exit block then
   // either this loop is already rotated or it is not
   // suitable for loop rotation transformations.
   if (!L->isLoopExit(OrigHeader))
     return false;

   BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
   if (!BI)
     return false;
   assert (BI->isConditional() && "Branch Instruction is not conditional");

   // Updating PHInodes in loops with multiple exits adds complexity.
   // Keep it simple, and restrict loop rotation to loops with one exit only.
   // In future, lift this restriction and support for multiple exits if
   // required.
   SmallVector<BasicBlock*, 8> ExitBlocks;
   L->getExitBlocks(ExitBlocks);
   if (ExitBlocks.size() > 1)
     return false;

   // Check size of original header and reject
   // loop if it is very big.
   if (OrigHeader->size() > MAX_HEADER_SIZE)
     return false;

   // Now, this loop is suitable for rotation.

   // Find new Loop header. NewHeader is a Header's one and only successor
   // that is inside loop.  Header's other successor is out side the
   // loop. Otherwise loop is not suitable for rotation.
   Exit = BI->getSuccessor(0);
   NewHeader = BI->getSuccessor(1);
   if (L->contains(Exit))
     std::swap(Exit, NewHeader);
   assert (NewHeader && "Unable to determine new loop header");
   assert(L->contains(NewHeader) && !L->contains(Exit) &&
          "Unable to determine loop header and exit blocks");

   // Copy PHI nodes and other instructions from original header
   // into original pre-header. Unlike original header, original pre-header is
   // not a member of loop.
   //
   // New loop header is one and only successor of original header that
   // is inside the loop. All other original header successors are outside
   // the loop. Copy PHI Nodes from original header into new loop header.
   // Add second incoming value, from original loop pre-header into these phi
   // nodes. If a value defined in original header is used outside original
   // header then new loop header will need new phi nodes with two incoming
   // values, one definition from original header and second definition is
   // from original loop pre-header.

   // Remove terminator from Original pre-header. Original pre-header will
   // receive a clone of original header terminator as a new terminator.
   OrigPreHeader->getInstList().pop_back();
   BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
   PHINode *PN = NULL;
   for (; (PN = dyn_cast<PHINode>(I)); ++I) {
     Instruction *In = I;

     // PHI nodes are not copied into original pre-header. Instead their values
     // are directly propagated.
     Value * NPV = PN->getIncomingValueForBlock(OrigPreHeader);

     // Create new PHI node with two incoming values for NewHeader.
     // One incoming value is from OrigLatch (through OrigHeader) and
     // second incoming value is from original pre-header.
     PHINode *NH = PHINode::Create(In->getType(), In->getName(),
                                   NewHeader->begin());
     NH->addIncoming(PN->getIncomingValueForBlock(OrigLatch), OrigHeader);
     NH->addIncoming(NPV, OrigPreHeader);

     // "In" can be replaced by NH at various places.
     LoopHeaderInfo.push_back(RenameData(In, NPV, NH));
   }

   // Now, handle non-phi instructions.
   for (; I != E; ++I) {
     Instruction *In = I;

     assert (!isa<PHINode>(In) && "PHINode is not expected here");
     // This is not a PHI instruction. Insert its clone into original pre-header.
     // If this instruction is using a value from same basic block then
     // update it to use value from cloned instruction.
     Instruction *C = In->clone();
     C->setName(In->getName());
     OrigPreHeader->getInstList().push_back(C);

     for (unsigned opi = 0, e = In->getNumOperands(); opi != e; ++opi) {
       if (Instruction *OpPhi = dyn_cast<PHINode>(In->getOperand(opi))) {
         if (const RenameData *D = findReplacementData(OpPhi)) {
           // This is using values from original header PHI node.
           // Here, directly used incoming value from original pre-header.
           C->setOperand(opi, D->PreHeader);
         }
       }
       else if (Instruction *OpInsn =
                dyn_cast<Instruction>(In->getOperand(opi))) {
         if (const RenameData *D = findReplacementData(OpInsn))
           C->setOperand(opi, D->PreHeader);
       }
     }


     // If this instruction is used outside this basic block then
     // create new PHINode for this instruction.
     Instruction *NewHeaderReplacement = NULL;
     if (usedOutsideOriginalHeader(In)) {
       PHINode *PN = PHINode::Create(In->getType(), In->getName(),
                                     NewHeader->begin());
       PN->addIncoming(In, OrigHeader);
       PN->addIncoming(C, OrigPreHeader);
       NewHeaderReplacement = PN;
     }
     LoopHeaderInfo.push_back(RenameData(In, C, NewHeaderReplacement));
   }

   // Rename uses of original header instructions to reflect their new
   // definitions (either from original pre-header node or from newly created
   // new header PHINodes.
   //
   // Original header instructions are used in
   // 1) Original header:
   //
   //    If instruction is used in non-phi instructions then it is using
   //    defintion from original heder iteself. Do not replace this use
   //    with definition from new header or original pre-header.
   //
   //    If instruction is used in phi node then it is an incoming
   //    value. Rename its use to reflect new definition from new-preheader
   //    or new header.
   //
   // 2) Inside loop but not in original header
   //
   //    Replace this use to reflect definition from new header.
   for(unsigned LHI = 0, LHI_E = LoopHeaderInfo.size(); LHI != LHI_E; ++LHI) {
     const RenameData &ILoopHeaderInfo = LoopHeaderInfo[LHI];

     if (!ILoopHeaderInfo.Header)
       continue;

     Instruction *OldPhi = ILoopHeaderInfo.Original;
     Instruction *NewPhi = ILoopHeaderInfo.Header;

     // Before replacing uses, collect them first, so that iterator is
     // not invalidated.
     SmallVector<Instruction *, 16> AllUses;
     for (Value::use_iterator UI = OldPhi->use_begin(), UE = OldPhi->use_end();
          UI != UE; ++UI) {
       Instruction *U = cast<Instruction>(UI);
       AllUses.push_back(U);
     }

     for (SmallVector<Instruction *, 16>::iterator UI = AllUses.begin(),
            UE = AllUses.end(); UI != UE; ++UI) {
       Instruction *U = *UI;
       BasicBlock *Parent = U->getParent();

       // Used inside original header
       if (Parent == OrigHeader) {
         // Do not rename uses inside original header non-phi instructions.
         PHINode *PU = dyn_cast<PHINode>(U);
         if (!PU)
           continue;

         // Do not rename uses inside original header phi nodes, if the
         // incoming value is for new header.
         if (PU->getBasicBlockIndex(NewHeader) != -1
             && PU->getIncomingValueForBlock(NewHeader) == U)
           continue;

        U->replaceUsesOfWith(OldPhi, NewPhi);
        continue;
       }

       // Used inside loop, but not in original header.
       if (L->contains(U->getParent())) {
         if (U != NewPhi)
           U->replaceUsesOfWith(OldPhi, NewPhi);
         continue;
       }

       // Used inside Exit Block. Since we are in LCSSA form, U must be PHINode.
       if (U->getParent() == Exit) {
         assert (isa<PHINode>(U) && "Use in Exit Block that is not PHINode");

         PHINode *UPhi = cast<PHINode>(U);
         // UPhi already has one incoming argument from original header.
         // Add second incoming argument from new Pre header.
         UPhi->addIncoming(ILoopHeaderInfo.PreHeader, OrigPreHeader);
       } else {
         // Used outside Exit block. Create a new PHI node from exit block
         // to receive value from ne new header ane pre header.
         PHINode *PN = PHINode::Create(U->getType(), U->getName(),
                                       Exit->begin());
         PN->addIncoming(ILoopHeaderInfo.PreHeader, OrigPreHeader);
         PN->addIncoming(OldPhi, OrigHeader);
         U->replaceUsesOfWith(OldPhi, PN);
       }
     }
   }

   /// Make sure all Exit block PHINodes have required incoming values.
   updateExitBlock();

   // Update CFG

   // Removing incoming branch from loop preheader to original header.
   // Now original header is inside the loop.
   for (BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
        I != E; ++I) {
     Instruction *In = I;
     PHINode *PN = dyn_cast<PHINode>(In);
     if (!PN)
       break;

     PN->removeIncomingValue(OrigPreHeader);
   }

   // Make NewHeader as the new header for the loop.
   L->moveToHeader(NewHeader);

   preserveCanonicalLoopForm(LPM);

   NumRotated++;
   return true;
 }

 /// Make sure all Exit block PHINodes have required incoming values.
 /// If incoming value is constant or defined outside the loop then
 /// PHINode may not have an entry for original pre-header.
 void LoopRotate::updateExitBlock() {

   for (BasicBlock::iterator I = Exit->begin(), E = Exit->end();
        I != E; ++I) {

     PHINode *PN = dyn_cast<PHINode>(I);
     if (!PN)
       break;

     // There is already one incoming value from original pre-header block.
     if (PN->getBasicBlockIndex(OrigPreHeader) != -1)
       continue;

     const RenameData *ILoopHeaderInfo;
     Value *V = PN->getIncomingValueForBlock(OrigHeader);
     if (isa<Instruction>(V) &&
         (ILoopHeaderInfo = findReplacementData(cast<Instruction>(V)))) {
       assert(ILoopHeaderInfo->PreHeader && "Missing New Preheader Instruction");
       PN->addIncoming(ILoopHeaderInfo->PreHeader, OrigPreHeader);
     } else {
       PN->addIncoming(V, OrigPreHeader);
     }
   }
 }

 /// Initialize local data
 void LoopRotate::initialize() {
   L = NULL;
   OrigHeader = NULL;
   OrigPreHeader = NULL;
   NewHeader = NULL;
   Exit = NULL;

   LoopHeaderInfo.clear();
 }

 /// Return true if this instruction is used by any instructions in the loop that
 /// aren't in original header.
 bool LoopRotate::usedOutsideOriginalHeader(Instruction *In) {

   for (Value::use_iterator UI = In->use_begin(), UE = In->use_end();
        UI != UE; ++UI) {
     Instruction *U = cast<Instruction>(UI);
     if (U->getParent() != OrigHeader) {
       if (L->contains(U->getParent()))
         return true;
     }
   }

   return false;
 }

 /// Find Replacement information for instruction. Return NULL if it is
 /// not available.
 const RenameData *LoopRotate::findReplacementData(Instruction *In) {

   // Since LoopHeaderInfo is small, linear walk is OK.
   for(unsigned LHI = 0, LHI_E = LoopHeaderInfo.size(); LHI != LHI_E; ++LHI) {
     const RenameData &ILoopHeaderInfo = LoopHeaderInfo[LHI];
     if (ILoopHeaderInfo.Original == In)
       return &ILoopHeaderInfo;
   }
   return NULL;
 }

 /// After loop rotation, loop pre-header has multiple sucessors.
 /// Insert one forwarding basic block to ensure that loop pre-header
 /// has only one successor.
 void LoopRotate::preserveCanonicalLoopForm(LPPassManager &LPM) {

   // Right now original pre-header has two successors, new header and
   // exit block. Insert new block between original pre-header and
   // new header such that loop's new pre-header has only one successor.
   BasicBlock *NewPreHeader = BasicBlock::Create("bb.nph",
                                                 OrigHeader->getParent(),
                                                 NewHeader);
   LoopInfo &LI = LPM.getAnalysis<LoopInfo>();
   if (Loop *PL = LI.getLoopFor(OrigPreHeader))
     PL->addBasicBlockToLoop(NewPreHeader, LI.getBase());
   BranchInst::Create(NewHeader, NewPreHeader);

   BranchInst *OrigPH_BI = cast<BranchInst>(OrigPreHeader->getTerminator());
   if (OrigPH_BI->getSuccessor(0) == NewHeader)
     OrigPH_BI->setSuccessor(0, NewPreHeader);
   else {
     assert (OrigPH_BI->getSuccessor(1) == NewHeader &&
             "Unexpected original pre-header terminator");
     OrigPH_BI->setSuccessor(1, NewPreHeader);
   }

   for (BasicBlock::iterator I = NewHeader->begin(), E = NewHeader->end();
        I != E; ++I) {
     Instruction *In = I;
     PHINode *PN = dyn_cast<PHINode>(In);
     if (!PN)
       break;

     int index = PN->getBasicBlockIndex(OrigPreHeader);
     assert (index != -1 && "Expected incoming value from Original PreHeader");
     PN->setIncomingBlock(index, NewPreHeader);
     assert (PN->getBasicBlockIndex(OrigPreHeader) == -1 &&
             "Expected only one incoming value from Original PreHeader");
   }

   if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
     DT->addNewBlock(NewPreHeader, OrigPreHeader);
     DT->changeImmediateDominator(L->getHeader(), NewPreHeader);
     DT->changeImmediateDominator(Exit, OrigPreHeader);
     for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end();
          BI != BE; ++BI) {
       BasicBlock *B = *BI;
       if (L->getHeader() != B) {
         DomTreeNode *Node = DT->getNode(B);
         if (Node && Node->getBlock() == OrigHeader)
           DT->changeImmediateDominator(*BI, L->getHeader());
       }
     }
     DT->changeImmediateDominator(OrigHeader, OrigLatch);
   }

   if(DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {

     // New Preheader's dominance frontier is Exit block.
     DominanceFrontier::DomSetType NewPHSet;
     NewPHSet.insert(Exit);
     DF->addBasicBlock(NewPreHeader, NewPHSet);

     // New Header's dominance frontier now includes itself and Exit block
     DominanceFrontier::iterator HeadI = DF->find(L->getHeader());
     if (HeadI != DF->end()) {
       DominanceFrontier::DomSetType & HeaderSet = HeadI->second;
       HeaderSet.clear();
       HeaderSet.insert(L->getHeader());
       HeaderSet.insert(Exit);
     } else {
       DominanceFrontier::DomSetType HeaderSet;
       HeaderSet.insert(L->getHeader());
       HeaderSet.insert(Exit);
       DF->addBasicBlock(L->getHeader(), HeaderSet);
     }

     // Original header (new Loop Latch)'s dominance frontier is Exit.
     DominanceFrontier::iterator LatchI = DF->find(L->getLoopLatch());
     if (LatchI != DF->end()) {
       DominanceFrontier::DomSetType &LatchSet = LatchI->second;
       LatchSet = LatchI->second;
       LatchSet.clear();
       LatchSet.insert(Exit);
     } else {
       DominanceFrontier::DomSetType LatchSet;
       LatchSet.insert(Exit);
       DF->addBasicBlock(L->getHeader(), LatchSet);
     }

     // If a loop block dominates new loop latch then its frontier is
     // new header and Exit.
     BasicBlock *NewLatch = L->getLoopLatch();
     DominatorTree *DT = getAnalysisToUpdate<DominatorTree>();
     for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end();
          BI != BE; ++BI) {
       BasicBlock *B = *BI;
       if (DT->dominates(B, NewLatch)) {
         DominanceFrontier::iterator BDFI = DF->find(B);
         if (BDFI != DF->end()) {
           DominanceFrontier::DomSetType &BSet = BDFI->second;
           BSet = BDFI->second;
           BSet.clear();
           BSet.insert(L->getHeader());
           BSet.insert(Exit);
         } else {
           DominanceFrontier::DomSetType BSet;
           BSet.insert(L->getHeader());
           BSet.insert(Exit);
           DF->addBasicBlock(B, BSet);
         }
       }
     }
   }

   // Preserve canonical loop form, which means Exit block should
   // have only one predecessor.
   BasicBlock *NExit = SplitEdge(L->getLoopLatch(), Exit, this);

   // Preserve LCSSA.
   BasicBlock::iterator I = Exit->begin(), E = Exit->end();
   PHINode *PN = NULL;
   for (; (PN = dyn_cast<PHINode>(I)); ++I) {
     unsigned N = PN->getNumIncomingValues();
     for (unsigned index = 0; index < N; ++index)
       if (PN->getIncomingBlock(index) == NExit) {
         PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName(),
                                          NExit->begin());
         NewPN->addIncoming(PN->getIncomingValue(index), L->getLoopLatch());
         PN->setIncomingValue(index, NewPN);
         PN->setIncomingBlock(index, NExit);
         break;
       }
   }

   assert (NewHeader && L->getHeader() == NewHeader
           && "Invalid loop header after loop rotation");
   assert (NewPreHeader && L->getLoopPreheader() == NewPreHeader
           && "Invalid loop preheader after loop rotation");
   assert (L->getLoopLatch()
           && "Invalid loop latch after loop rotation");

 }
	//===- LoopRotation.cpp - Loop Rotation Pass ------------------------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This file implements Loop Rotation Pass.
	//
	//===----------------------------------------------------------------------===//

	#define DEBUG_TYPE "loop-rotate"

	#include "llvm/Transforms/Scalar.h"
	#include "llvm/Function.h"
	#include "llvm/Instructions.h"
	#include "llvm/Analysis/LoopInfo.h"
	#include "llvm/Analysis/LoopPass.h"
	#include "llvm/Analysis/Dominators.h"
	#include "llvm/Analysis/ScalarEvolution.h"
	#include "llvm/Transforms/Utils/Local.h"
	#include "llvm/Transforms/Utils/BasicBlockUtils.h"
	#include "llvm/Support/CommandLine.h"
	#include "llvm/Support/Debug.h"
	#include "llvm/ADT/Statistic.h"
	#include "llvm/ADT/SmallVector.h"

	using namespace llvm;

	#define MAX_HEADER_SIZE 16

	STATISTIC(NumRotated, "Number of loops rotated");
	namespace {

	class VISIBILITY_HIDDEN RenameData {
	public:
	RenameData(Instruction O, Value P, Instruction *H)
	: Original(O), PreHeader(P), Header(H) { }
	public:
	Instruction *Original; // Original instruction
	Value *PreHeader; // Original pre-header replacement
	Instruction *Header; // New header replacement
	};

	class VISIBILITY_HIDDEN LoopRotate : public LoopPass {

	public:
	static char ID; // Pass ID, replacement for typeid
	LoopRotate() : LoopPass(&ID) {}

	// Rotate Loop L as many times as possible. Return true if
	// loop is rotated at least once.
	bool runOnLoop(Loop *L, LPPassManager &LPM);

	// LCSSA form makes instruction renaming easier.
	virtual void getAnalysisUsage(AnalysisUsage &AU) const {
	AU.addRequiredID(LoopSimplifyID);
	AU.addPreservedID(LoopSimplifyID);
	AU.addRequiredID(LCSSAID);
	AU.addPreservedID(LCSSAID);
	AU.addPreserved<ScalarEvolution>();
	AU.addPreserved<LoopInfo>();
	AU.addPreserved<DominatorTree>();
	AU.addPreserved<DominanceFrontier>();
	}

	// Helper functions

	/// Do actual work
	bool rotateLoop(Loop *L, LPPassManager &LPM);

	/// Initialize local data
	void initialize();

	/// Make sure all Exit block PHINodes have required incoming values.
	/// If incoming value is constant or defined outside the loop then
	/// PHINode may not have an entry for original pre-header.
	void updateExitBlock();

	/// Return true if this instruction is used outside original header.
	bool usedOutsideOriginalHeader(Instruction *In);

	/// Find Replacement information for instruction. Return NULL if it is
	/// not available.
	const RenameData findReplacementData(Instruction I);

	/// After loop rotation, loop pre-header has multiple sucessors.
	/// Insert one forwarding basic block to ensure that loop pre-header
	/// has only one successor.
	void preserveCanonicalLoopForm(LPPassManager &LPM);

	private:

	Loop *L;
	BasicBlock *OrigHeader;
	BasicBlock *OrigPreHeader;
	BasicBlock *OrigLatch;
	BasicBlock *NewHeader;
	BasicBlock *Exit;
	LPPassManager *LPM_Ptr;
	SmallVector<RenameData, MAX_HEADER_SIZE> LoopHeaderInfo;
	};
	}

	char LoopRotate::ID = 0;
	static RegisterPass<LoopRotate> X("loop-rotate", "Rotate Loops");

	Pass *llvm::createLoopRotatePass() { return new LoopRotate(); }

	/// Rotate Loop L as many times as possible. Return true if
	/// loop is rotated at least once.
	bool LoopRotate::runOnLoop(Loop *Lp, LPPassManager &LPM) {

	bool RotatedOneLoop = false;
	initialize();
	LPM_Ptr = &LPM;

	// One loop can be rotated multiple times.
	while (rotateLoop(Lp,LPM)) {
	RotatedOneLoop = true;
	initialize();
	}

	return RotatedOneLoop;
	}

	/// Rotate loop LP. Return true if the loop is rotated.
	bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) {

	L = Lp;

	OrigHeader = L->getHeader();
	OrigPreHeader = L->getLoopPreheader();
	OrigLatch = L->getLoopLatch();

	// If loop has only one block then there is not much to rotate.
	if (L->getBlocks().size() == 1)
	return false;

	assert (OrigHeader && OrigLatch && OrigPreHeader &&
	"Loop is not in canonical form");

	// If loop header is not one of the loop exit block then
	// either this loop is already rotated or it is not
	// suitable for loop rotation transformations.
	if (!L->isLoopExit(OrigHeader))
	return false;

	BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
	if (!BI)
	return false;
	assert (BI->isConditional() && "Branch Instruction is not conditional");

	// Updating PHInodes in loops with multiple exits adds complexity.
	// Keep it simple, and restrict loop rotation to loops with one exit only.
	// In future, lift this restriction and support for multiple exits if
	// required.
	SmallVector<BasicBlock*, 8> ExitBlocks;
	L->getExitBlocks(ExitBlocks);
	if (ExitBlocks.size() > 1)
	return false;

	// Check size of original header and reject
	// loop if it is very big.
	if (OrigHeader->size() > MAX_HEADER_SIZE)
	return false;

	// Now, this loop is suitable for rotation.

	// Find new Loop header. NewHeader is a Header's one and only successor
	// that is inside loop. Header's other successor is out side the
	// loop. Otherwise loop is not suitable for rotation.
	Exit = BI->getSuccessor(0);
	NewHeader = BI->getSuccessor(1);
	if (L->contains(Exit))
	std::swap(Exit, NewHeader);
	assert (NewHeader && "Unable to determine new loop header");
	assert(L->contains(NewHeader) && !L->contains(Exit) &&
	"Unable to determine loop header and exit blocks");

	// Copy PHI nodes and other instructions from original header
	// into original pre-header. Unlike original header, original pre-header is
	// not a member of loop.
	//
	// New loop header is one and only successor of original header that
	// is inside the loop. All other original header successors are outside
	// the loop. Copy PHI Nodes from original header into new loop header.
	// Add second incoming value, from original loop pre-header into these phi
	// nodes. If a value defined in original header is used outside original
	// header then new loop header will need new phi nodes with two incoming
	// values, one definition from original header and second definition is
	// from original loop pre-header.

	// Remove terminator from Original pre-header. Original pre-header will
	// receive a clone of original header terminator as a new terminator.
	OrigPreHeader->getInstList().pop_back();
	BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
	PHINode *PN = NULL;
	for (; (PN = dyn_cast<PHINode>(I)); ++I) {
	Instruction *In = I;

	// PHI nodes are not copied into original pre-header. Instead their values
	// are directly propagated.
	Value * NPV = PN->getIncomingValueForBlock(OrigPreHeader);

	// Create new PHI node with two incoming values for NewHeader.
	// One incoming value is from OrigLatch (through OrigHeader) and
	// second incoming value is from original pre-header.
	PHINode *NH = PHINode::Create(In->getType(), In->getName(),
	NewHeader->begin());
	NH->addIncoming(PN->getIncomingValueForBlock(OrigLatch), OrigHeader);
	NH->addIncoming(NPV, OrigPreHeader);

	// "In" can be replaced by NH at various places.
	LoopHeaderInfo.push_back(RenameData(In, NPV, NH));
	}

	// Now, handle non-phi instructions.
	for (; I != E; ++I) {
	Instruction *In = I;

	assert (!isa<PHINode>(In) && "PHINode is not expected here");
	// This is not a PHI instruction. Insert its clone into original pre-header.
	// If this instruction is using a value from same basic block then
	// update it to use value from cloned instruction.
	Instruction *C = In->clone();
	C->setName(In->getName());
	OrigPreHeader->getInstList().push_back(C);

	for (unsigned opi = 0, e = In->getNumOperands(); opi != e; ++opi) {
	if (Instruction *OpPhi = dyn_cast<PHINode>(In->getOperand(opi))) {
	if (const RenameData *D = findReplacementData(OpPhi)) {
	// This is using values from original header PHI node.
	// Here, directly used incoming value from original pre-header.
	C->setOperand(opi, D->PreHeader);
	}
	}
	else if (Instruction *OpInsn =
	dyn_cast<Instruction>(In->getOperand(opi))) {
	if (const RenameData *D = findReplacementData(OpInsn))
	C->setOperand(opi, D->PreHeader);
	}
	}


	// If this instruction is used outside this basic block then
	// create new PHINode for this instruction.
	Instruction *NewHeaderReplacement = NULL;
	if (usedOutsideOriginalHeader(In)) {
	PHINode *PN = PHINode::Create(In->getType(), In->getName(),
	NewHeader->begin());
	PN->addIncoming(In, OrigHeader);
	PN->addIncoming(C, OrigPreHeader);
	NewHeaderReplacement = PN;
	}
	LoopHeaderInfo.push_back(RenameData(In, C, NewHeaderReplacement));
	}

	// Rename uses of original header instructions to reflect their new
	// definitions (either from original pre-header node or from newly created
	// new header PHINodes.
	//
	// Original header instructions are used in
	// 1) Original header:
	//
	// If instruction is used in non-phi instructions then it is using
	// defintion from original heder iteself. Do not replace this use
	// with definition from new header or original pre-header.
	//
	// If instruction is used in phi node then it is an incoming
	// value. Rename its use to reflect new definition from new-preheader
	// or new header.
	//
	// 2) Inside loop but not in original header
	//
	// Replace this use to reflect definition from new header.
	for(unsigned LHI = 0, LHI_E = LoopHeaderInfo.size(); LHI != LHI_E; ++LHI) {
	const RenameData &ILoopHeaderInfo = LoopHeaderInfo[LHI];

	if (!ILoopHeaderInfo.Header)
	continue;

	Instruction *OldPhi = ILoopHeaderInfo.Original;
	Instruction *NewPhi = ILoopHeaderInfo.Header;

	// Before replacing uses, collect them first, so that iterator is
	// not invalidated.
	SmallVector<Instruction *, 16> AllUses;
	for (Value::use_iterator UI = OldPhi->use_begin(), UE = OldPhi->use_end();
	UI != UE; ++UI) {
	Instruction *U = cast<Instruction>(UI);
	AllUses.push_back(U);
	}

	for (SmallVector<Instruction *, 16>::iterator UI = AllUses.begin(),
	UE = AllUses.end(); UI != UE; ++UI) {
	Instruction U = UI;
	BasicBlock *Parent = U->getParent();

	// Used inside original header
	if (Parent == OrigHeader) {
	// Do not rename uses inside original header non-phi instructions.
	PHINode *PU = dyn_cast<PHINode>(U);
	if (!PU)
	continue;

	// Do not rename uses inside original header phi nodes, if the
	// incoming value is for new header.
	if (PU->getBasicBlockIndex(NewHeader) != -1
	&& PU->getIncomingValueForBlock(NewHeader) == U)
	continue;

	U->replaceUsesOfWith(OldPhi, NewPhi);
	continue;
	}

	// Used inside loop, but not in original header.
	if (L->contains(U->getParent())) {
	if (U != NewPhi)
	U->replaceUsesOfWith(OldPhi, NewPhi);
	continue;
	}

	// Used inside Exit Block. Since we are in LCSSA form, U must be PHINode.
	if (U->getParent() == Exit) {
	assert (isa<PHINode>(U) && "Use in Exit Block that is not PHINode");

	PHINode *UPhi = cast<PHINode>(U);
	// UPhi already has one incoming argument from original header.
	// Add second incoming argument from new Pre header.
	UPhi->addIncoming(ILoopHeaderInfo.PreHeader, OrigPreHeader);
	} else {
	// Used outside Exit block. Create a new PHI node from exit block
	// to receive value from ne new header ane pre header.
	PHINode *PN = PHINode::Create(U->getType(), U->getName(),
	Exit->begin());
	PN->addIncoming(ILoopHeaderInfo.PreHeader, OrigPreHeader);
	PN->addIncoming(OldPhi, OrigHeader);
	U->replaceUsesOfWith(OldPhi, PN);
	}
	}
	}

	/// Make sure all Exit block PHINodes have required incoming values.
	updateExitBlock();

	// Update CFG

	// Removing incoming branch from loop preheader to original header.
	// Now original header is inside the loop.
	for (BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
	I != E; ++I) {
	Instruction *In = I;
	PHINode *PN = dyn_cast<PHINode>(In);
	if (!PN)
	break;

	PN->removeIncomingValue(OrigPreHeader);
	}

	// Make NewHeader as the new header for the loop.
	L->moveToHeader(NewHeader);

	preserveCanonicalLoopForm(LPM);

	NumRotated++;
	return true;
	}

	/// Make sure all Exit block PHINodes have required incoming values.
	/// If incoming value is constant or defined outside the loop then
	/// PHINode may not have an entry for original pre-header.
	void LoopRotate::updateExitBlock() {

	for (BasicBlock::iterator I = Exit->begin(), E = Exit->end();
	I != E; ++I) {

	PHINode *PN = dyn_cast<PHINode>(I);
	if (!PN)
	break;

	// There is already one incoming value from original pre-header block.
	if (PN->getBasicBlockIndex(OrigPreHeader) != -1)
	continue;

	const RenameData *ILoopHeaderInfo;
	Value *V = PN->getIncomingValueForBlock(OrigHeader);
	if (isa<Instruction>(V) &&
	(ILoopHeaderInfo = findReplacementData(cast<Instruction>(V)))) {
	assert(ILoopHeaderInfo->PreHeader && "Missing New Preheader Instruction");
	PN->addIncoming(ILoopHeaderInfo->PreHeader, OrigPreHeader);
	} else {
	PN->addIncoming(V, OrigPreHeader);
	}
	}
	}

	/// Initialize local data
	void LoopRotate::initialize() {
	L = NULL;
	OrigHeader = NULL;
	OrigPreHeader = NULL;
	NewHeader = NULL;
	Exit = NULL;

	LoopHeaderInfo.clear();
	}

	/// Return true if this instruction is used by any instructions in the loop that
	/// aren't in original header.
	bool LoopRotate::usedOutsideOriginalHeader(Instruction *In) {

	for (Value::use_iterator UI = In->use_begin(), UE = In->use_end();
	UI != UE; ++UI) {
	Instruction *U = cast<Instruction>(UI);
	if (U->getParent() != OrigHeader) {
	if (L->contains(U->getParent()))
	return true;
	}
	}

	return false;
	}

	/// Find Replacement information for instruction. Return NULL if it is
	/// not available.
	const RenameData LoopRotate::findReplacementData(Instruction In) {

	// Since LoopHeaderInfo is small, linear walk is OK.
	for(unsigned LHI = 0, LHI_E = LoopHeaderInfo.size(); LHI != LHI_E; ++LHI) {
	const RenameData &ILoopHeaderInfo = LoopHeaderInfo[LHI];
	if (ILoopHeaderInfo.Original == In)
	return &ILoopHeaderInfo;
	}
	return NULL;
	}

	/// After loop rotation, loop pre-header has multiple sucessors.
	/// Insert one forwarding basic block to ensure that loop pre-header
	/// has only one successor.
	void LoopRotate::preserveCanonicalLoopForm(LPPassManager &LPM) {

	// Right now original pre-header has two successors, new header and
	// exit block. Insert new block between original pre-header and
	// new header such that loop's new pre-header has only one successor.
	BasicBlock *NewPreHeader = BasicBlock::Create("bb.nph",
	OrigHeader->getParent(),
	NewHeader);
	LoopInfo &LI = LPM.getAnalysis<LoopInfo>();
	if (Loop *PL = LI.getLoopFor(OrigPreHeader))
	PL->addBasicBlockToLoop(NewPreHeader, LI.getBase());
	BranchInst::Create(NewHeader, NewPreHeader);

	BranchInst *OrigPH_BI = cast<BranchInst>(OrigPreHeader->getTerminator());
	if (OrigPH_BI->getSuccessor(0) == NewHeader)
	OrigPH_BI->setSuccessor(0, NewPreHeader);
	else {
	assert (OrigPH_BI->getSuccessor(1) == NewHeader &&
	"Unexpected original pre-header terminator");
	OrigPH_BI->setSuccessor(1, NewPreHeader);
	}

	for (BasicBlock::iterator I = NewHeader->begin(), E = NewHeader->end();
	I != E; ++I) {
	Instruction *In = I;
	PHINode *PN = dyn_cast<PHINode>(In);
	if (!PN)
	break;

	int index = PN->getBasicBlockIndex(OrigPreHeader);
	assert (index != -1 && "Expected incoming value from Original PreHeader");
	PN->setIncomingBlock(index, NewPreHeader);
	assert (PN->getBasicBlockIndex(OrigPreHeader) == -1 &&
	"Expected only one incoming value from Original PreHeader");
	}

	if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
	DT->addNewBlock(NewPreHeader, OrigPreHeader);
	DT->changeImmediateDominator(L->getHeader(), NewPreHeader);
	DT->changeImmediateDominator(Exit, OrigPreHeader);
	for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end();
	BI != BE; ++BI) {
	BasicBlock B = BI;
	if (L->getHeader() != B) {
	DomTreeNode *Node = DT->getNode(B);
	if (Node && Node->getBlock() == OrigHeader)
	DT->changeImmediateDominator(*BI, L->getHeader());
	}
	}
	DT->changeImmediateDominator(OrigHeader, OrigLatch);
	}

	if(DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {

	// New Preheader's dominance frontier is Exit block.
	DominanceFrontier::DomSetType NewPHSet;
	NewPHSet.insert(Exit);
	DF->addBasicBlock(NewPreHeader, NewPHSet);

	// New Header's dominance frontier now includes itself and Exit block
	DominanceFrontier::iterator HeadI = DF->find(L->getHeader());
	if (HeadI != DF->end()) {
	DominanceFrontier::DomSetType & HeaderSet = HeadI->second;
	HeaderSet.clear();
	HeaderSet.insert(L->getHeader());
	HeaderSet.insert(Exit);
	} else {
	DominanceFrontier::DomSetType HeaderSet;
	HeaderSet.insert(L->getHeader());
	HeaderSet.insert(Exit);
	DF->addBasicBlock(L->getHeader(), HeaderSet);
	}

	// Original header (new Loop Latch)'s dominance frontier is Exit.
	DominanceFrontier::iterator LatchI = DF->find(L->getLoopLatch());
	if (LatchI != DF->end()) {
	DominanceFrontier::DomSetType &LatchSet = LatchI->second;
	LatchSet = LatchI->second;
	LatchSet.clear();
	LatchSet.insert(Exit);
	} else {
	DominanceFrontier::DomSetType LatchSet;
	LatchSet.insert(Exit);
	DF->addBasicBlock(L->getHeader(), LatchSet);
	}

	// If a loop block dominates new loop latch then its frontier is
	// new header and Exit.
	BasicBlock *NewLatch = L->getLoopLatch();
	DominatorTree *DT = getAnalysisToUpdate<DominatorTree>();
	for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end();
	BI != BE; ++BI) {
	BasicBlock B = BI;
	if (DT->dominates(B, NewLatch)) {
	DominanceFrontier::iterator BDFI = DF->find(B);
	if (BDFI != DF->end()) {
	DominanceFrontier::DomSetType &BSet = BDFI->second;
	BSet = BDFI->second;
	BSet.clear();
	BSet.insert(L->getHeader());
	BSet.insert(Exit);
	} else {
	DominanceFrontier::DomSetType BSet;
	BSet.insert(L->getHeader());
	BSet.insert(Exit);
	DF->addBasicBlock(B, BSet);
	}
	}
	}
	}

	// Preserve canonical loop form, which means Exit block should
	// have only one predecessor.
	BasicBlock *NExit = SplitEdge(L->getLoopLatch(), Exit, this);

	// Preserve LCSSA.
	BasicBlock::iterator I = Exit->begin(), E = Exit->end();
	PHINode *PN = NULL;
	for (; (PN = dyn_cast<PHINode>(I)); ++I) {
	unsigned N = PN->getNumIncomingValues();
	for (unsigned index = 0; index < N; ++index)
	if (PN->getIncomingBlock(index) == NExit) {
	PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName(),
	NExit->begin());
	NewPN->addIncoming(PN->getIncomingValue(index), L->getLoopLatch());
	PN->setIncomingValue(index, NewPN);
	PN->setIncomingBlock(index, NExit);
	break;
	}
	}

	assert (NewHeader && L->getHeader() == NewHeader
	&& "Invalid loop header after loop rotation");
	assert (NewPreHeader && L->getLoopPreheader() == NewPreHeader
	&& "Invalid loop preheader after loop rotation");
	assert (L->getLoopLatch()
	&& "Invalid loop latch after loop rotation");

	}