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Diffstat (limited to 'contrib/llvm/lib/Transforms/Utils/LoopUnroll.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Utils/LoopUnroll.cpp | 778 |
1 files changed, 778 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/contrib/llvm/lib/Transforms/Utils/LoopUnroll.cpp new file mode 100644 index 000000000000..e346ebd6a000 --- /dev/null +++ b/contrib/llvm/lib/Transforms/Utils/LoopUnroll.cpp @@ -0,0 +1,778 @@ +//===-- UnrollLoop.cpp - Loop unrolling utilities -------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements some loop unrolling utilities. It does not define any +// actual pass or policy, but provides a single function to perform loop +// unrolling. +// +// The process of unrolling can produce extraneous basic blocks linked with +// unconditional branches. This will be corrected in the future. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Utils/UnrollLoop.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AssumptionCache.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/LoopIterator.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/OptimizationDiagnosticInfo.h" +#include "llvm/Analysis/ScalarEvolution.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Cloning.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Transforms/Utils/LoopSimplify.h" +#include "llvm/Transforms/Utils/LoopUtils.h" +#include "llvm/Transforms/Utils/SimplifyIndVar.h" +using namespace llvm; + +#define DEBUG_TYPE "loop-unroll" + +// TODO: Should these be here or in LoopUnroll? +STATISTIC(NumCompletelyUnrolled, "Number of loops completely unrolled"); +STATISTIC(NumUnrolled, "Number of loops unrolled (completely or otherwise)"); + +static cl::opt<bool> +UnrollRuntimeEpilog("unroll-runtime-epilog", cl::init(false), cl::Hidden, + cl::desc("Allow runtime unrolled loops to be unrolled " + "with epilog instead of prolog.")); + +/// Convert the instruction operands from referencing the current values into +/// those specified by VMap. +static inline void remapInstruction(Instruction *I, + ValueToValueMapTy &VMap) { + for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { + Value *Op = I->getOperand(op); + ValueToValueMapTy::iterator It = VMap.find(Op); + if (It != VMap.end()) + I->setOperand(op, It->second); + } + + if (PHINode *PN = dyn_cast<PHINode>(I)) { + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + ValueToValueMapTy::iterator It = VMap.find(PN->getIncomingBlock(i)); + if (It != VMap.end()) + PN->setIncomingBlock(i, cast<BasicBlock>(It->second)); + } + } +} + +/// Folds a basic block into its predecessor if it only has one predecessor, and +/// that predecessor only has one successor. +/// The LoopInfo Analysis that is passed will be kept consistent. If folding is +/// successful references to the containing loop must be removed from +/// ScalarEvolution by calling ScalarEvolution::forgetLoop because SE may have +/// references to the eliminated BB. The argument ForgottenLoops contains a set +/// of loops that have already been forgotten to prevent redundant, expensive +/// calls to ScalarEvolution::forgetLoop. Returns the new combined block. +static BasicBlock * +foldBlockIntoPredecessor(BasicBlock *BB, LoopInfo *LI, ScalarEvolution *SE, + SmallPtrSetImpl<Loop *> &ForgottenLoops, + DominatorTree *DT) { + // Merge basic blocks into their predecessor if there is only one distinct + // pred, and if there is only one distinct successor of the predecessor, and + // if there are no PHI nodes. + BasicBlock *OnlyPred = BB->getSinglePredecessor(); + if (!OnlyPred) return nullptr; + + if (OnlyPred->getTerminator()->getNumSuccessors() != 1) + return nullptr; + + DEBUG(dbgs() << "Merging: " << *BB << "into: " << *OnlyPred); + + // Resolve any PHI nodes at the start of the block. They are all + // guaranteed to have exactly one entry if they exist, unless there are + // multiple duplicate (but guaranteed to be equal) entries for the + // incoming edges. This occurs when there are multiple edges from + // OnlyPred to OnlySucc. + FoldSingleEntryPHINodes(BB); + + // Delete the unconditional branch from the predecessor... + OnlyPred->getInstList().pop_back(); + + // Make all PHI nodes that referred to BB now refer to Pred as their + // source... + BB->replaceAllUsesWith(OnlyPred); + + // Move all definitions in the successor to the predecessor... + OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList()); + + // OldName will be valid until erased. + StringRef OldName = BB->getName(); + + // Erase the old block and update dominator info. + if (DT) + if (DomTreeNode *DTN = DT->getNode(BB)) { + DomTreeNode *PredDTN = DT->getNode(OnlyPred); + SmallVector<DomTreeNode *, 8> Children(DTN->begin(), DTN->end()); + for (auto *DI : Children) + DT->changeImmediateDominator(DI, PredDTN); + + DT->eraseNode(BB); + } + + // ScalarEvolution holds references to loop exit blocks. + if (SE) { + if (Loop *L = LI->getLoopFor(BB)) { + if (ForgottenLoops.insert(L).second) + SE->forgetLoop(L); + } + } + LI->removeBlock(BB); + + // Inherit predecessor's name if it exists... + if (!OldName.empty() && !OnlyPred->hasName()) + OnlyPred->setName(OldName); + + BB->eraseFromParent(); + + return OnlyPred; +} + +/// Check if unrolling created a situation where we need to insert phi nodes to +/// preserve LCSSA form. +/// \param Blocks is a vector of basic blocks representing unrolled loop. +/// \param L is the outer loop. +/// It's possible that some of the blocks are in L, and some are not. In this +/// case, if there is a use is outside L, and definition is inside L, we need to +/// insert a phi-node, otherwise LCSSA will be broken. +/// The function is just a helper function for llvm::UnrollLoop that returns +/// true if this situation occurs, indicating that LCSSA needs to be fixed. +static bool needToInsertPhisForLCSSA(Loop *L, std::vector<BasicBlock *> Blocks, + LoopInfo *LI) { + for (BasicBlock *BB : Blocks) { + if (LI->getLoopFor(BB) == L) + continue; + for (Instruction &I : *BB) { + for (Use &U : I.operands()) { + if (auto Def = dyn_cast<Instruction>(U)) { + Loop *DefLoop = LI->getLoopFor(Def->getParent()); + if (!DefLoop) + continue; + if (DefLoop->contains(L)) + return true; + } + } + } + } + return false; +} + +/// Adds ClonedBB to LoopInfo, creates a new loop for ClonedBB if necessary +/// and adds a mapping from the original loop to the new loop to NewLoops. +/// Returns nullptr if no new loop was created and a pointer to the +/// original loop OriginalBB was part of otherwise. +const Loop* llvm::addClonedBlockToLoopInfo(BasicBlock *OriginalBB, + BasicBlock *ClonedBB, LoopInfo *LI, + NewLoopsMap &NewLoops) { + // Figure out which loop New is in. + const Loop *OldLoop = LI->getLoopFor(OriginalBB); + assert(OldLoop && "Should (at least) be in the loop being unrolled!"); + + Loop *&NewLoop = NewLoops[OldLoop]; + if (!NewLoop) { + // Found a new sub-loop. + assert(OriginalBB == OldLoop->getHeader() && + "Header should be first in RPO"); + + NewLoop = new Loop(); + Loop *NewLoopParent = NewLoops.lookup(OldLoop->getParentLoop()); + + if (NewLoopParent) + NewLoopParent->addChildLoop(NewLoop); + else + LI->addTopLevelLoop(NewLoop); + + NewLoop->addBasicBlockToLoop(ClonedBB, *LI); + return OldLoop; + } else { + NewLoop->addBasicBlockToLoop(ClonedBB, *LI); + return nullptr; + } +} + +/// Unroll the given loop by Count. The loop must be in LCSSA form. Returns true +/// if unrolling was successful, or false if the loop was unmodified. Unrolling +/// can only fail when the loop's latch block is not terminated by a conditional +/// branch instruction. However, if the trip count (and multiple) are not known, +/// loop unrolling will mostly produce more code that is no faster. +/// +/// TripCount is the upper bound of the iteration on which control exits +/// LatchBlock. Control may exit the loop prior to TripCount iterations either +/// via an early branch in other loop block or via LatchBlock terminator. This +/// is relaxed from the general definition of trip count which is the number of +/// times the loop header executes. Note that UnrollLoop assumes that the loop +/// counter test is in LatchBlock in order to remove unnecesssary instances of +/// the test. If control can exit the loop from the LatchBlock's terminator +/// prior to TripCount iterations, flag PreserveCondBr needs to be set. +/// +/// PreserveCondBr indicates whether the conditional branch of the LatchBlock +/// needs to be preserved. It is needed when we use trip count upper bound to +/// fully unroll the loop. If PreserveOnlyFirst is also set then only the first +/// conditional branch needs to be preserved. +/// +/// Similarly, TripMultiple divides the number of times that the LatchBlock may +/// execute without exiting the loop. +/// +/// If AllowRuntime is true then UnrollLoop will consider unrolling loops that +/// have a runtime (i.e. not compile time constant) trip count. Unrolling these +/// loops require a unroll "prologue" that runs "RuntimeTripCount % Count" +/// iterations before branching into the unrolled loop. UnrollLoop will not +/// runtime-unroll the loop if computing RuntimeTripCount will be expensive and +/// AllowExpensiveTripCount is false. +/// +/// If we want to perform PGO-based loop peeling, PeelCount is set to the +/// number of iterations we want to peel off. +/// +/// The LoopInfo Analysis that is passed will be kept consistent. +/// +/// This utility preserves LoopInfo. It will also preserve ScalarEvolution and +/// DominatorTree if they are non-null. +bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount, bool Force, + bool AllowRuntime, bool AllowExpensiveTripCount, + bool PreserveCondBr, bool PreserveOnlyFirst, + unsigned TripMultiple, unsigned PeelCount, LoopInfo *LI, + ScalarEvolution *SE, DominatorTree *DT, + AssumptionCache *AC, OptimizationRemarkEmitter *ORE, + bool PreserveLCSSA) { + + BasicBlock *Preheader = L->getLoopPreheader(); + if (!Preheader) { + DEBUG(dbgs() << " Can't unroll; loop preheader-insertion failed.\n"); + return false; + } + + BasicBlock *LatchBlock = L->getLoopLatch(); + if (!LatchBlock) { + DEBUG(dbgs() << " Can't unroll; loop exit-block-insertion failed.\n"); + return false; + } + + // Loops with indirectbr cannot be cloned. + if (!L->isSafeToClone()) { + DEBUG(dbgs() << " Can't unroll; Loop body cannot be cloned.\n"); + return false; + } + + BasicBlock *Header = L->getHeader(); + BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator()); + + if (!BI || BI->isUnconditional()) { + // The loop-rotate pass can be helpful to avoid this in many cases. + DEBUG(dbgs() << + " Can't unroll; loop not terminated by a conditional branch.\n"); + return false; + } + + if (Header->hasAddressTaken()) { + // The loop-rotate pass can be helpful to avoid this in many cases. + DEBUG(dbgs() << + " Won't unroll loop: address of header block is taken.\n"); + return false; + } + + if (TripCount != 0) + DEBUG(dbgs() << " Trip Count = " << TripCount << "\n"); + if (TripMultiple != 1) + DEBUG(dbgs() << " Trip Multiple = " << TripMultiple << "\n"); + + // Effectively "DCE" unrolled iterations that are beyond the tripcount + // and will never be executed. + if (TripCount != 0 && Count > TripCount) + Count = TripCount; + + // Don't enter the unroll code if there is nothing to do. + if (TripCount == 0 && Count < 2 && PeelCount == 0) + return false; + + assert(Count > 0); + assert(TripMultiple > 0); + assert(TripCount == 0 || TripCount % TripMultiple == 0); + + // Are we eliminating the loop control altogether? + bool CompletelyUnroll = Count == TripCount; + SmallVector<BasicBlock *, 4> ExitBlocks; + L->getExitBlocks(ExitBlocks); + std::vector<BasicBlock*> OriginalLoopBlocks = L->getBlocks(); + + // Go through all exits of L and see if there are any phi-nodes there. We just + // conservatively assume that they're inserted to preserve LCSSA form, which + // means that complete unrolling might break this form. We need to either fix + // it in-place after the transformation, or entirely rebuild LCSSA. TODO: For + // now we just recompute LCSSA for the outer loop, but it should be possible + // to fix it in-place. + bool NeedToFixLCSSA = PreserveLCSSA && CompletelyUnroll && + any_of(ExitBlocks, [](const BasicBlock *BB) { + return isa<PHINode>(BB->begin()); + }); + + // We assume a run-time trip count if the compiler cannot + // figure out the loop trip count and the unroll-runtime + // flag is specified. + bool RuntimeTripCount = (TripCount == 0 && Count > 0 && AllowRuntime); + + assert((!RuntimeTripCount || !PeelCount) && + "Did not expect runtime trip-count unrolling " + "and peeling for the same loop"); + + if (PeelCount) + peelLoop(L, PeelCount, LI, SE, DT, PreserveLCSSA); + + // Loops containing convergent instructions must have a count that divides + // their TripMultiple. + DEBUG( + { + bool HasConvergent = false; + for (auto &BB : L->blocks()) + for (auto &I : *BB) + if (auto CS = CallSite(&I)) + HasConvergent |= CS.isConvergent(); + assert((!HasConvergent || TripMultiple % Count == 0) && + "Unroll count must divide trip multiple if loop contains a " + "convergent operation."); + }); + + if (RuntimeTripCount && TripMultiple % Count != 0 && + !UnrollRuntimeLoopRemainder(L, Count, AllowExpensiveTripCount, + UnrollRuntimeEpilog, LI, SE, DT, + PreserveLCSSA)) { + if (Force) + RuntimeTripCount = false; + else + return false; + } + + // Notify ScalarEvolution that the loop will be substantially changed, + // if not outright eliminated. + if (SE) + SE->forgetLoop(L); + + // If we know the trip count, we know the multiple... + unsigned BreakoutTrip = 0; + if (TripCount != 0) { + BreakoutTrip = TripCount % Count; + TripMultiple = 0; + } else { + // Figure out what multiple to use. + BreakoutTrip = TripMultiple = + (unsigned)GreatestCommonDivisor64(Count, TripMultiple); + } + + using namespace ore; + // Report the unrolling decision. + if (CompletelyUnroll) { + DEBUG(dbgs() << "COMPLETELY UNROLLING loop %" << Header->getName() + << " with trip count " << TripCount << "!\n"); + ORE->emit(OptimizationRemark(DEBUG_TYPE, "FullyUnrolled", L->getStartLoc(), + L->getHeader()) + << "completely unrolled loop with " + << NV("UnrollCount", TripCount) << " iterations"); + } else if (PeelCount) { + DEBUG(dbgs() << "PEELING loop %" << Header->getName() + << " with iteration count " << PeelCount << "!\n"); + ORE->emit(OptimizationRemark(DEBUG_TYPE, "Peeled", L->getStartLoc(), + L->getHeader()) + << " peeled loop by " << NV("PeelCount", PeelCount) + << " iterations"); + } else { + OptimizationRemark Diag(DEBUG_TYPE, "PartialUnrolled", L->getStartLoc(), + L->getHeader()); + Diag << "unrolled loop by a factor of " << NV("UnrollCount", Count); + + DEBUG(dbgs() << "UNROLLING loop %" << Header->getName() + << " by " << Count); + if (TripMultiple == 0 || BreakoutTrip != TripMultiple) { + DEBUG(dbgs() << " with a breakout at trip " << BreakoutTrip); + ORE->emit(Diag << " with a breakout at trip " + << NV("BreakoutTrip", BreakoutTrip)); + } else if (TripMultiple != 1) { + DEBUG(dbgs() << " with " << TripMultiple << " trips per branch"); + ORE->emit(Diag << " with " << NV("TripMultiple", TripMultiple) + << " trips per branch"); + } else if (RuntimeTripCount) { + DEBUG(dbgs() << " with run-time trip count"); + ORE->emit(Diag << " with run-time trip count"); + } + DEBUG(dbgs() << "!\n"); + } + + bool ContinueOnTrue = L->contains(BI->getSuccessor(0)); + BasicBlock *LoopExit = BI->getSuccessor(ContinueOnTrue); + + // For the first iteration of the loop, we should use the precloned values for + // PHI nodes. Insert associations now. + ValueToValueMapTy LastValueMap; + std::vector<PHINode*> OrigPHINode; + for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { + OrigPHINode.push_back(cast<PHINode>(I)); + } + + std::vector<BasicBlock*> Headers; + std::vector<BasicBlock*> Latches; + Headers.push_back(Header); + Latches.push_back(LatchBlock); + + // The current on-the-fly SSA update requires blocks to be processed in + // reverse postorder so that LastValueMap contains the correct value at each + // exit. + LoopBlocksDFS DFS(L); + DFS.perform(LI); + + // Stash the DFS iterators before adding blocks to the loop. + LoopBlocksDFS::RPOIterator BlockBegin = DFS.beginRPO(); + LoopBlocksDFS::RPOIterator BlockEnd = DFS.endRPO(); + + std::vector<BasicBlock*> UnrolledLoopBlocks = L->getBlocks(); + + // Loop Unrolling might create new loops. While we do preserve LoopInfo, we + // might break loop-simplified form for these loops (as they, e.g., would + // share the same exit blocks). We'll keep track of loops for which we can + // break this so that later we can re-simplify them. + SmallSetVector<Loop *, 4> LoopsToSimplify; + for (Loop *SubLoop : *L) + LoopsToSimplify.insert(SubLoop); + + for (unsigned It = 1; It != Count; ++It) { + std::vector<BasicBlock*> NewBlocks; + SmallDenseMap<const Loop *, Loop *, 4> NewLoops; + NewLoops[L] = L; + + for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) { + ValueToValueMapTy VMap; + BasicBlock *New = CloneBasicBlock(*BB, VMap, "." + Twine(It)); + Header->getParent()->getBasicBlockList().push_back(New); + + // Tell LI about New. + if (*BB == Header) { + assert(LI->getLoopFor(*BB) == L && "Header should not be in a sub-loop"); + L->addBasicBlockToLoop(New, *LI); + } else { + const Loop *OldLoop = addClonedBlockToLoopInfo(*BB, New, LI, NewLoops); + if (OldLoop) { + LoopsToSimplify.insert(NewLoops[OldLoop]); + + // Forget the old loop, since its inputs may have changed. + if (SE) + SE->forgetLoop(OldLoop); + } + } + + if (*BB == Header) + // Loop over all of the PHI nodes in the block, changing them to use + // the incoming values from the previous block. + for (PHINode *OrigPHI : OrigPHINode) { + PHINode *NewPHI = cast<PHINode>(VMap[OrigPHI]); + Value *InVal = NewPHI->getIncomingValueForBlock(LatchBlock); + if (Instruction *InValI = dyn_cast<Instruction>(InVal)) + if (It > 1 && L->contains(InValI)) + InVal = LastValueMap[InValI]; + VMap[OrigPHI] = InVal; + New->getInstList().erase(NewPHI); + } + + // Update our running map of newest clones + LastValueMap[*BB] = New; + for (ValueToValueMapTy::iterator VI = VMap.begin(), VE = VMap.end(); + VI != VE; ++VI) + LastValueMap[VI->first] = VI->second; + + // Add phi entries for newly created values to all exit blocks. + for (BasicBlock *Succ : successors(*BB)) { + if (L->contains(Succ)) + continue; + for (BasicBlock::iterator BBI = Succ->begin(); + PHINode *phi = dyn_cast<PHINode>(BBI); ++BBI) { + Value *Incoming = phi->getIncomingValueForBlock(*BB); + ValueToValueMapTy::iterator It = LastValueMap.find(Incoming); + if (It != LastValueMap.end()) + Incoming = It->second; + phi->addIncoming(Incoming, New); + } + } + // Keep track of new headers and latches as we create them, so that + // we can insert the proper branches later. + if (*BB == Header) + Headers.push_back(New); + if (*BB == LatchBlock) + Latches.push_back(New); + + NewBlocks.push_back(New); + UnrolledLoopBlocks.push_back(New); + + // Update DomTree: since we just copy the loop body, and each copy has a + // dedicated entry block (copy of the header block), this header's copy + // dominates all copied blocks. That means, dominance relations in the + // copied body are the same as in the original body. + if (DT) { + if (*BB == Header) + DT->addNewBlock(New, Latches[It - 1]); + else { + auto BBDomNode = DT->getNode(*BB); + auto BBIDom = BBDomNode->getIDom(); + BasicBlock *OriginalBBIDom = BBIDom->getBlock(); + DT->addNewBlock( + New, cast<BasicBlock>(LastValueMap[cast<Value>(OriginalBBIDom)])); + } + } + } + + // Remap all instructions in the most recent iteration + for (BasicBlock *NewBlock : NewBlocks) { + for (Instruction &I : *NewBlock) { + ::remapInstruction(&I, LastValueMap); + if (auto *II = dyn_cast<IntrinsicInst>(&I)) + if (II->getIntrinsicID() == Intrinsic::assume) + AC->registerAssumption(II); + } + } + } + + // Loop over the PHI nodes in the original block, setting incoming values. + for (PHINode *PN : OrigPHINode) { + if (CompletelyUnroll) { + PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader)); + Header->getInstList().erase(PN); + } + else if (Count > 1) { + Value *InVal = PN->removeIncomingValue(LatchBlock, false); + // If this value was defined in the loop, take the value defined by the + // last iteration of the loop. + if (Instruction *InValI = dyn_cast<Instruction>(InVal)) { + if (L->contains(InValI)) + InVal = LastValueMap[InVal]; + } + assert(Latches.back() == LastValueMap[LatchBlock] && "bad last latch"); + PN->addIncoming(InVal, Latches.back()); + } + } + + // Now that all the basic blocks for the unrolled iterations are in place, + // set up the branches to connect them. + for (unsigned i = 0, e = Latches.size(); i != e; ++i) { + // The original branch was replicated in each unrolled iteration. + BranchInst *Term = cast<BranchInst>(Latches[i]->getTerminator()); + + // The branch destination. + unsigned j = (i + 1) % e; + BasicBlock *Dest = Headers[j]; + bool NeedConditional = true; + + if (RuntimeTripCount && j != 0) { + NeedConditional = false; + } + + // For a complete unroll, make the last iteration end with a branch + // to the exit block. + if (CompletelyUnroll) { + if (j == 0) + Dest = LoopExit; + // If using trip count upper bound to completely unroll, we need to keep + // the conditional branch except the last one because the loop may exit + // after any iteration. + assert(NeedConditional && + "NeedCondition cannot be modified by both complete " + "unrolling and runtime unrolling"); + NeedConditional = (PreserveCondBr && j && !(PreserveOnlyFirst && i != 0)); + } else if (j != BreakoutTrip && (TripMultiple == 0 || j % TripMultiple != 0)) { + // If we know the trip count or a multiple of it, we can safely use an + // unconditional branch for some iterations. + NeedConditional = false; + } + + if (NeedConditional) { + // Update the conditional branch's successor for the following + // iteration. + Term->setSuccessor(!ContinueOnTrue, Dest); + } else { + // Remove phi operands at this loop exit + if (Dest != LoopExit) { + BasicBlock *BB = Latches[i]; + for (BasicBlock *Succ: successors(BB)) { + if (Succ == Headers[i]) + continue; + for (BasicBlock::iterator BBI = Succ->begin(); + PHINode *Phi = dyn_cast<PHINode>(BBI); ++BBI) { + Phi->removeIncomingValue(BB, false); + } + } + } + // Replace the conditional branch with an unconditional one. + BranchInst::Create(Dest, Term); + Term->eraseFromParent(); + } + } + // Update dominators of blocks we might reach through exits. + // Immediate dominator of such block might change, because we add more + // routes which can lead to the exit: we can now reach it from the copied + // iterations too. Thus, the new idom of the block will be the nearest + // common dominator of the previous idom and common dominator of all copies of + // the previous idom. This is equivalent to the nearest common dominator of + // the previous idom and the first latch, which dominates all copies of the + // previous idom. + if (DT && Count > 1) { + for (auto *BB : OriginalLoopBlocks) { + auto *BBDomNode = DT->getNode(BB); + SmallVector<BasicBlock *, 16> ChildrenToUpdate; + for (auto *ChildDomNode : BBDomNode->getChildren()) { + auto *ChildBB = ChildDomNode->getBlock(); + if (!L->contains(ChildBB)) + ChildrenToUpdate.push_back(ChildBB); + } + BasicBlock *NewIDom = DT->findNearestCommonDominator(BB, Latches[0]); + for (auto *ChildBB : ChildrenToUpdate) + DT->changeImmediateDominator(ChildBB, NewIDom); + } + } + + // Merge adjacent basic blocks, if possible. + SmallPtrSet<Loop *, 4> ForgottenLoops; + for (BasicBlock *Latch : Latches) { + BranchInst *Term = cast<BranchInst>(Latch->getTerminator()); + if (Term->isUnconditional()) { + BasicBlock *Dest = Term->getSuccessor(0); + if (BasicBlock *Fold = + foldBlockIntoPredecessor(Dest, LI, SE, ForgottenLoops, DT)) { + // Dest has been folded into Fold. Update our worklists accordingly. + std::replace(Latches.begin(), Latches.end(), Dest, Fold); + UnrolledLoopBlocks.erase(std::remove(UnrolledLoopBlocks.begin(), + UnrolledLoopBlocks.end(), Dest), + UnrolledLoopBlocks.end()); + } + } + } + + // FIXME: We only preserve DT info for complete unrolling now. Incrementally + // updating domtree after partial loop unrolling should also be easy. + if (DT && !CompletelyUnroll) + DT->recalculate(*L->getHeader()->getParent()); + else if (DT) + DEBUG(DT->verifyDomTree()); + + // Simplify any new induction variables in the partially unrolled loop. + if (SE && !CompletelyUnroll && Count > 1) { + SmallVector<WeakVH, 16> DeadInsts; + simplifyLoopIVs(L, SE, DT, LI, DeadInsts); + + // Aggressively clean up dead instructions that simplifyLoopIVs already + // identified. Any remaining should be cleaned up below. + while (!DeadInsts.empty()) + if (Instruction *Inst = + dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val())) + RecursivelyDeleteTriviallyDeadInstructions(Inst); + } + + // At this point, the code is well formed. We now do a quick sweep over the + // inserted code, doing constant propagation and dead code elimination as we + // go. + const DataLayout &DL = Header->getModule()->getDataLayout(); + const std::vector<BasicBlock*> &NewLoopBlocks = L->getBlocks(); + for (BasicBlock *BB : NewLoopBlocks) { + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { + Instruction *Inst = &*I++; + + if (Value *V = SimplifyInstruction(Inst, DL)) + if (LI->replacementPreservesLCSSAForm(Inst, V)) + Inst->replaceAllUsesWith(V); + if (isInstructionTriviallyDead(Inst)) + BB->getInstList().erase(Inst); + } + } + + // TODO: after peeling or unrolling, previously loop variant conditions are + // likely to fold to constants, eagerly propagating those here will require + // fewer cleanup passes to be run. Alternatively, a LoopEarlyCSE might be + // appropriate. + + NumCompletelyUnrolled += CompletelyUnroll; + ++NumUnrolled; + + Loop *OuterL = L->getParentLoop(); + // Update LoopInfo if the loop is completely removed. + if (CompletelyUnroll) + LI->markAsRemoved(L); + + // After complete unrolling most of the blocks should be contained in OuterL. + // However, some of them might happen to be out of OuterL (e.g. if they + // precede a loop exit). In this case we might need to insert PHI nodes in + // order to preserve LCSSA form. + // We don't need to check this if we already know that we need to fix LCSSA + // form. + // TODO: For now we just recompute LCSSA for the outer loop in this case, but + // it should be possible to fix it in-place. + if (PreserveLCSSA && OuterL && CompletelyUnroll && !NeedToFixLCSSA) + NeedToFixLCSSA |= ::needToInsertPhisForLCSSA(OuterL, UnrolledLoopBlocks, LI); + + // If we have a pass and a DominatorTree we should re-simplify impacted loops + // to ensure subsequent analyses can rely on this form. We want to simplify + // at least one layer outside of the loop that was unrolled so that any + // changes to the parent loop exposed by the unrolling are considered. + if (DT) { + if (!OuterL && !CompletelyUnroll) + OuterL = L; + if (OuterL) { + // OuterL includes all loops for which we can break loop-simplify, so + // it's sufficient to simplify only it (it'll recursively simplify inner + // loops too). + // TODO: That potentially might be compile-time expensive. We should try + // to fix the loop-simplified form incrementally. + simplifyLoop(OuterL, DT, LI, SE, AC, PreserveLCSSA); + + // LCSSA must be performed on the outermost affected loop. The unrolled + // loop's last loop latch is guaranteed to be in the outermost loop after + // LoopInfo's been updated by markAsRemoved. + Loop *LatchLoop = LI->getLoopFor(Latches.back()); + if (!OuterL->contains(LatchLoop)) + while (OuterL->getParentLoop() != LatchLoop) + OuterL = OuterL->getParentLoop(); + + if (NeedToFixLCSSA) + formLCSSARecursively(*OuterL, *DT, LI, SE); + else + assert(OuterL->isLCSSAForm(*DT) && + "Loops should be in LCSSA form after loop-unroll."); + } else { + // Simplify loops for which we might've broken loop-simplify form. + for (Loop *SubLoop : LoopsToSimplify) + simplifyLoop(SubLoop, DT, LI, SE, AC, PreserveLCSSA); + } + } + + return true; +} + +/// Given an llvm.loop loop id metadata node, returns the loop hint metadata +/// node with the given name (for example, "llvm.loop.unroll.count"). If no +/// such metadata node exists, then nullptr is returned. +MDNode *llvm::GetUnrollMetadata(MDNode *LoopID, StringRef Name) { + // First operand should refer to the loop id itself. + assert(LoopID->getNumOperands() > 0 && "requires at least one operand"); + assert(LoopID->getOperand(0) == LoopID && "invalid loop id"); + + for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) { + MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i)); + if (!MD) + continue; + + MDString *S = dyn_cast<MDString>(MD->getOperand(0)); + if (!S) + continue; + + if (Name.equals(S->getString())) + return MD; + } + return nullptr; +} |