diff --git a/lib/Transforms/Scalar/LoopRotation.cpp b/lib/Transforms/Scalar/LoopRotation.cpp index 70c69bb1dae..c8cbad479a3 100644 --- a/lib/Transforms/Scalar/LoopRotation.cpp +++ b/lib/Transforms/Scalar/LoopRotation.cpp @@ -21,6 +21,7 @@ #include "llvm/Analysis/ScalarEvolution.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/SSAUpdater.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/ADT/Statistic.h" @@ -32,16 +33,6 @@ using namespace llvm; STATISTIC(NumRotated, "Number of loops rotated"); namespace { - class 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 LoopRotate : public LoopPass { public: static char ID; // Pass ID, replacement for typeid @@ -71,25 +62,12 @@ namespace { /// 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; @@ -97,7 +75,6 @@ namespace { BasicBlock *NewHeader; BasicBlock *Exit; LPPassManager *LPM_Ptr; - SmallVector LoopHeaderInfo; }; } @@ -199,168 +176,88 @@ bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) { "New header doesn't have one pred!"); FoldSingleEntryPHINodes(NewHeader); - // Copy PHI nodes and other instructions from the original header - // into the original pre-header. Unlike the original header, the original - // pre-header is not a member of the loop. - // - // The new loop header is the 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 the original header into the 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(); + // Begin by walking OrigHeader and populating ValueMap with an entry for + // each Instruction. BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end(); - PHINode *PN = 0; - for (; (PN = dyn_cast(I)); ++I) { - // PHI nodes are not copied into original pre-header. Instead their values - // are directly propagated. - Value *NPV = PN->getIncomingValueForBlock(OrigPreHeader); + DenseMap ValueMap; - // Create a new PHI node with two incoming values for NewHeader. - // One incoming value is from OrigLatch (through OrigHeader) and the - // second incoming value is from original pre-header. - PHINode *NH = PHINode::Create(PN->getType(), PN->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(PN, NPV, NH)); - } + // For PHI nodes, the value available in OldPreHeader is just the + // incoming value from OldPreHeader. + for (; PHINode *PN = dyn_cast(I); ++I) + ValueMap[PN] = PN->getIncomingValue(PN->getBasicBlockIndex(OrigPreHeader)); - // Now, handle non-phi instructions. + // For the rest of the instructions, create a clone in the OldPreHeader. + TerminatorInst *LoopEntryBranch = OrigPreHeader->getTerminator(); for (; I != E; ++I) { - Instruction *In = I; - assert(!isa(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) { - Instruction *OpInsn = dyn_cast(In->getOperand(opi)); - if (!OpInsn) continue; // Ignore non-instruction values. - 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)); + Instruction *C = I->clone(); + C->setName(I->getName()); + C->insertBefore(LoopEntryBranch); + ValueMap[I] = C; } - // 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]; + // Along with all the other instructions, we just cloned OrigHeader's + // terminator into OrigPreHeader. Fix up the PHI nodes in each of OrigHeader's + // successors by duplicating their incoming values for OrigHeader. + TerminatorInst *TI = OrigHeader->getTerminator(); + for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) + for (BasicBlock::iterator BI = TI->getSuccessor(i)->begin(); + PHINode *PN = dyn_cast(BI); ++BI) + PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreHeader); - if (!ILoopHeaderInfo.Header) - continue; + // Now that OrigPreHeader has a clone of OrigHeader's terminator, remove + // OrigPreHeader's old terminator (the original branch into the loop), and + // remove the corresponding incoming values from the PHI nodes in OrigHeader. + LoopEntryBranch->eraseFromParent(); + for (I = OrigHeader->begin(); PHINode *PN = dyn_cast(I); ++I) + PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreHeader)); - Instruction *OldPhi = ILoopHeaderInfo.Original; - Instruction *NewPhi = ILoopHeaderInfo.Header; + // Now fix up users of the instructions in OrigHeader, insertting PHI nodes + // as necessary. + SSAUpdater SSA; + for (I = OrigHeader->begin(); I != E; ++I) { + Value *OrigHeaderVal = I; + Value *OrigPreHeaderVal = ValueMap[OrigHeaderVal]; - // Before replacing uses, collect them first, so that iterator is - // not invalidated. - SmallVector AllUses; - for (Value::use_iterator UI = OldPhi->use_begin(), UE = OldPhi->use_end(); - UI != UE; ++UI) - AllUses.push_back(cast(UI)); + // The value now exits in two versions: the initial value in the preheader + // and the loop "next" value in the original header. + SSA.Initialize(OrigHeaderVal); + SSA.AddAvailableValue(OrigHeader, OrigHeaderVal); + SSA.AddAvailableValue(OrigPreHeader, OrigPreHeaderVal); - for (SmallVector::iterator UI = AllUses.begin(), - UE = AllUses.end(); UI != UE; ++UI) { - Instruction *U = *UI; - BasicBlock *Parent = U->getParent(); + // Visit each use of the OrigHeader instruction. + for (Value::use_iterator UI = OrigHeaderVal->use_begin(), + UE = OrigHeaderVal->use_end(); UI != UE; ) { + // Grab the use before incrementing the iterator. + Use &U = UI.getUse(); - // Used inside original header - if (Parent == OrigHeader) { - // Do not rename uses inside original header non-phi instructions. - PHINode *PU = dyn_cast(U); - if (!PU) + // Increment the iterator before removing the use from the list. + ++UI; + + // SSAUpdater can't handle a non-PHI use in the same block as an + // earlier def. We can easily handle those cases manually. + Instruction *UserInst = cast(U.getUser()); + if (!isa(UserInst)) { + BasicBlock *UserBB = UserInst->getParent(); + + // The original users in the OrigHeader are already using the + // original definitions. + if (UserBB == OrigHeader) 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) + // Users in the OrigPreHeader need to use the value to which the + // original definitions are mapped. + if (UserBB == OrigPreHeader) { + U = OrigPreHeaderVal; 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(U) && "Use in Exit Block that is not PHINode"); - - PHINode *UPhi = cast(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 in the exit block - // to receive the value from the new header and 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); - } + // Anything else can be handled by SSAUpdater. + SSA.RewriteUse(U); } } - - /// 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(); - (PN = dyn_cast(I)); ++I) - PN->removeIncomingValue(OrigPreHeader); - - // Make NewHeader as the new header for the loop. + // NewHeader is now the header of the loop. L->moveToHeader(NewHeader); preserveCanonicalLoopForm(LPM); @@ -369,31 +266,6 @@ bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) { return true; } -/// Make sure all Exit block PHINodes have required incoming values. -/// If an incoming value is constant or defined outside the loop then -/// PHINode may not have an entry for the original pre-header. -void LoopRotate::updateExitBlock() { - - PHINode *PN; - for (BasicBlock::iterator I = Exit->begin(); - (PN = dyn_cast(I)); ++I) { - - // 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(V) && - (ILoopHeaderInfo = findReplacementData(cast(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; @@ -401,34 +273,6 @@ void LoopRotate::initialize() { 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) { - BasicBlock *UserBB = cast(UI)->getParent(); - if (UserBB != OrigHeader && L->contains(UserBB)) - 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.