--- /dev/null
+//===- LoopRotation.cpp - Loop Rotation Pass ------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file was developed by Devang Patel and 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-rotation"
+
+#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/Transforms/Utils/Local.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/SmallVector.h"
+#include <map>
+
+using namespace llvm;
+
+#define MAX_HEADER_SIZE 16
+
+STATISTIC(NumRotated, "Number of loops rotated");
+namespace {
+
+ cl::opt<unsigned>
+ RotateThreshold("rotate-threshold", cl::init(200), cl::Hidden,
+ cl::desc("The cut-off point for loop rotating"));
+
+ class VISIBILITY_HIDDEN InsnReplacementData {
+ public:
+ InsnReplacementData(Instruction *O, Instruction *P, Instruction *H)
+ : Original(O), PreHeader(P), Header(H) {}
+ public:
+ Instruction *Original; // Original instruction
+ Instruction *PreHeader; // New pre-header replacement
+ Instruction *Header; // New header replacement
+ };
+
+ class VISIBILITY_HIDDEN LoopRotate : public LoopPass {
+
+ public:
+ bool runOnLoop(Loop *L, LPPassManager &LPM);
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequiredID(LCSSAID);
+ AU.addPreservedID(LCSSAID);
+ //AU.addRequired<LoopInfo>();
+ //AU.addPreserved<LoopInfo>();
+ }
+
+ // 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 new 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.
+ InsnReplacementData *findReplacementData(Instruction *I);
+
+ private:
+
+ Loop *L;
+ BasicBlock *OrigHeader;
+ BasicBlock *OrigPreHeader;
+ BasicBlock *OrigLatch;
+ BasicBlock *NewHeader;
+ BasicBlock *NewPreHeader;
+ BasicBlock *Exit;
+
+ SmallVector<InsnReplacementData, MAX_HEADER_SIZE> RD;
+ };
+
+ RegisterPass<LoopRotate> X ("loop-rotate", "Rotate Loops");
+}
+
+LoopPass *llvm::createLoopRotatePass() { return new LoopRotate(); }
+
+bool LoopRotate::runOnLoop(Loop *Lp, LPPassManager &LPM) {
+
+ bool RotatedOneLoop = false;
+ initialize();
+
+ // One loop can be rotated multiple times.
+ while (rotateLoop(Lp,LPM)) {
+ RotatedOneLoop = true;
+ initialize();
+ }
+
+ return RotatedOneLoop;
+}
+
+bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) {
+
+ L = Lp;
+ if ( NumRotated >= RotateThreshold)
+ return false;
+
+ 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;
+
+ if (!OrigHeader || !OrigLatch || !OrigPreHeader)
+ return false;
+
+ // 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;
+
+ std::vector<BasicBlock *> ExitBlocks;
+ L->getExitBlocks(ExitBlocks);
+ if (ExitBlocks.size() > 1)
+ return false;
+
+ // Find new Loop header. NewHeader is a Header's one and only successor
+ // that is inside loop. Header's all other successors are out side the
+ // loop. Otherwise loop is not suitable for rotation.
+ for (unsigned index = 0; index < BI->getNumSuccessors(); ++index) {
+ BasicBlock *S = BI->getSuccessor(index);
+ if (L->contains(S)) {
+ if (!NewHeader)
+ NewHeader = S;
+ else
+ // Loop Header has two successors inside loop. This loop is
+ // not suitable for rotation.
+ return false;
+ } else {
+ if (!Exit)
+ Exit = S;
+ else
+ // Loop has multiple exits.
+ return false;
+ }
+ }
+ assert (NewHeader && "Unable to determine new loop header");
+
+ // Check size of original header and reject
+ // loop if it is very big.
+ if (OrigHeader->getInstList().size() > MAX_HEADER_SIZE)
+ return false;
+
+ // Now, this loop is suitable for rotation.
+
+ // Copy Prepare PHI nodes and other instructions from original header
+ // into new pre-header. Unlike original header, new pre-header is
+ // not a member of loop. New pre-header has only one predecessor,
+ // that is original loop pre-header.
+ //
+ // 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 new 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 new loop pre-header (which is a clone of original header definition).
+
+ NewPreHeader = new BasicBlock("bb.nph", OrigHeader->getParent(), OrigHeader);
+ for (BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
+ I != E; ++I) {
+ Instruction *In = I;
+
+ if (PHINode *PN = dyn_cast<PHINode>(I)) {
+
+ // Create new PHI node with one value incoming from OrigPreHeader.
+ // NewPreHeader has only one predecessor, OrigPreHeader.
+ PHINode *NPH = new PHINode(In->getType(), In->getName());
+ NPH->addIncoming(PN->getIncomingValueForBlock(OrigPreHeader),
+ OrigPreHeader);
+ NewPreHeader->getInstList().push_back(NPH);
+
+ // Create new PHI node with two incoming values for NewHeader.
+ // One incoming value is from OrigLatch (through OrigHeader) and
+ // second incoming value is from NewPreHeader.
+ PHINode *NH = new PHINode(In->getType(), In->getName());
+ NH->addIncoming(PN->getIncomingValueForBlock(OrigLatch), OrigHeader);
+ NH->addIncoming(NPH, NewPreHeader);
+ NewHeader->getInstList().push_front(NH);
+
+ RD.push_back(InsnReplacementData(In, NPH, NH));
+ } else {
+ // This is not a PHI instruction. Insert its clone into NewPreHeader.
+ // 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());
+ NewPreHeader->getInstList().push_back(C);
+
+ // If this instruction is used outside this basic block then
+ // create new PHINode for this instruction.
+ Instruction *NewHeaderReplacement = NULL;
+ if (usedOutsideOriginalHeader(In)) {
+ PHINode *PN = new PHINode(In->getType(), In->getName());
+ PN->addIncoming(In, OrigHeader);
+ PN->addIncoming(C, NewPreHeader);
+ NewHeader->getInstList().push_front(PN);
+ NewHeaderReplacement = PN;
+ }
+ RD.push_back(InsnReplacementData(In, C, NewHeaderReplacement));
+ }
+ }
+
+ // Update new pre-header.
+ // Rename values that are defined in original header to reflects values
+ // defined in new pre-header.
+ for (SmallVector<InsnReplacementData, MAX_HEADER_SIZE>::iterator
+ I = RD.begin(), E = RD.end(); I != E; ++I) {
+
+ InsnReplacementData IRD = (*I);
+ Instruction *In = IRD.Original;
+ Instruction *C = IRD.PreHeader;
+
+ if (C->getParent() != NewPreHeader)
+ continue;
+
+ // PHINodes uses value from pre-header predecessors.
+ if (isa<PHINode>(In))
+ continue;
+
+ for (unsigned opi = 0; opi < In->getNumOperands(); ++opi) {
+ if (Instruction *OpPhi = dyn_cast<PHINode>(In->getOperand(opi))) {
+ if (InsnReplacementData *D = findReplacementData(OpPhi))
+ C->setOperand(opi, D->PreHeader);
+ }
+ else if (Instruction *OpInsn =
+ dyn_cast<Instruction>(In->getOperand(opi))) {
+ if (InsnReplacementData *D = findReplacementData(OpInsn))
+ C->setOperand(opi, D->PreHeader);
+ }
+ }
+ }
+
+ // Rename uses of original header instructions to reflect their new
+ // definitions (either from new 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 new 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 (SmallVector<InsnReplacementData, MAX_HEADER_SIZE>::iterator
+ I = RD.begin(), E = RD.end(); I != E; ++I) {
+
+ InsnReplacementData IRD = (*I);
+ if (!IRD.Header)
+ continue;
+
+ Instruction *OldPhi = IRD.Original;
+ Instruction *NewPhi = IRD.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.
+ if (!isa<PHINode>(U))
+ continue;
+ PHINode *PU = dyn_cast<PHINode>(U);
+ // 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.
+ assert ( U->getParent() == Exit && "Need to propagate new PHI into Exit blocks");
+ 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(IRD.PreHeader, NewPreHeader);
+ }
+ }
+
+ /// 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.
+ OrigHeader->removePredecessor(OrigPreHeader);
+
+ // Establish NewPreHeader as loop preheader. Add unconditional branch
+ // from original loop pre-header to new loop pre-header. Add NewPreHEader
+ // in loop nest.
+ BranchInst *PH_BI = cast<BranchInst>(OrigPreHeader->getTerminator());
+ PH_BI->setSuccessor(0, NewPreHeader);
+ LoopInfo &LI = LPM.getAnalysis<LoopInfo>();
+ if (Loop *PL = LI.getLoopFor(OrigPreHeader))
+ PL->addBasicBlockToLoop(NewPreHeader, LI);
+
+ // Make NewHeader as the new header for the loop.
+ L->moveToHeader(NewHeader);
+
+ 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 new pre-header.
+void LoopRotate::updateExitBlock() {
+
+ for (BasicBlock::iterator I = Exit->begin(), E = Exit->end();
+ I != E; ++I) {
+
+ if (!isa<PHINode>(I))
+ break;
+
+ PHINode *PN = dyn_cast<PHINode>(I);
+
+ if (PN->getBasicBlockIndex(NewPreHeader) == -1) {
+ Value *V = PN->getIncomingValueForBlock(OrigHeader);
+ if (isa<Constant>(V))
+ PN->addIncoming(V, NewPreHeader);
+ else {
+ InsnReplacementData *IRD = findReplacementData(cast<Instruction>(V));
+ assert (IRD && IRD->PreHeader && "Missing New Preheader Instruction");
+ PN->addIncoming(IRD->PreHeader, NewPreHeader);
+ }
+ }
+ }
+}
+
+
+/// Initialize local data
+void LoopRotate::initialize() {
+ L = NULL;
+ OrigHeader = NULL;
+ OrigPreHeader = NULL;
+ NewHeader = NULL;
+ NewPreHeader = NULL;
+ Exit = NULL;
+
+ RD.clear();
+}
+
+/// Return true if this instruction is used outside 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.
+InsnReplacementData *LoopRotate::findReplacementData(Instruction *In) {
+
+ // Since RD is small, linear walk is OK.
+ for (SmallVector<InsnReplacementData, MAX_HEADER_SIZE>::iterator
+ I = RD.begin(), E = RD.end(); I != E; ++I)
+ if ((*I).Original == In)
+ return &(*I);
+
+ return NULL;
+}
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