| //===-- 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/ScalarEvolution.h" |
| #include "llvm/IR/BasicBlock.h" |
| #include "llvm/IR/DataLayout.h" |
| #include "llvm/IR/DiagnosticInfo.h" |
| #include "llvm/IR/Dominators.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/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(true), 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; |
| } |
| |
| /// 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 generally defined as the number of times the loop header |
| /// executes. UnrollLoop relaxes the definition to permit early exits: here |
| /// TripCount is the iteration on which control exits LatchBlock if no early |
| /// exits were taken. Note that UnrollLoop assumes that the loop counter test |
| /// terminates LatchBlock in order to remove unnecesssary instances of the |
| /// test. In other words, control may exit the loop prior to TripCount |
| /// iterations via an early branch, but control may not exit the loop from the |
| /// LatchBlock's terminator prior to TripCount iterations. |
| /// |
| /// 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. |
| /// |
| /// 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 AllowRuntime, bool AllowExpensiveTripCount, |
| unsigned TripMultiple, LoopInfo *LI, ScalarEvolution *SE, |
| DominatorTree *DT, AssumptionCache *AC, |
| 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. This way we don't |
| // need to support "partial unrolling by 1". |
| if (TripCount == 0 && Count < 2) |
| 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 && |
| std::any_of(ExitBlocks.begin(), ExitBlocks.end(), |
| [&](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); |
| |
| // 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."); |
| }); |
| // Don't output the runtime loop remainder if Count is a multiple of |
| // TripMultiple. Such a remainder is never needed, and is unsafe if the loop |
| // contains a convergent instruction. |
| if (RuntimeTripCount && TripMultiple % Count != 0 && |
| !UnrollRuntimeLoopRemainder(L, Count, AllowExpensiveTripCount, |
| UnrollRuntimeEpilog, LI, SE, DT, |
| PreserveLCSSA)) |
| 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); |
| } |
| |
| // Report the unrolling decision. |
| DebugLoc LoopLoc = L->getStartLoc(); |
| Function *F = Header->getParent(); |
| LLVMContext &Ctx = F->getContext(); |
| |
| if (CompletelyUnroll) { |
| DEBUG(dbgs() << "COMPLETELY UNROLLING loop %" << Header->getName() |
| << " with trip count " << TripCount << "!\n"); |
| emitOptimizationRemark(Ctx, DEBUG_TYPE, *F, LoopLoc, |
| Twine("completely unrolled loop with ") + |
| Twine(TripCount) + " iterations"); |
| } else { |
| auto EmitDiag = [&](const Twine &T) { |
| emitOptimizationRemark(Ctx, DEBUG_TYPE, *F, LoopLoc, |
| "unrolled loop by a factor of " + Twine(Count) + |
| T); |
| }; |
| |
| DEBUG(dbgs() << "UNROLLING loop %" << Header->getName() |
| << " by " << Count); |
| if (TripMultiple == 0 || BreakoutTrip != TripMultiple) { |
| DEBUG(dbgs() << " with a breakout at trip " << BreakoutTrip); |
| EmitDiag(" with a breakout at trip " + Twine(BreakoutTrip)); |
| } else if (TripMultiple != 1) { |
| DEBUG(dbgs() << " with " << TripMultiple << " trips per branch"); |
| EmitDiag(" with " + Twine(TripMultiple) + " trips per branch"); |
| } else if (RuntimeTripCount) { |
| DEBUG(dbgs() << " with run-time trip count"); |
| EmitDiag(" 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(); |
| 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 { |
| // Figure out which loop New is in. |
| const Loop *OldLoop = LI->getLoopFor(*BB); |
| assert(OldLoop && "Should (at least) be in the loop being unrolled!"); |
| |
| Loop *&NewLoop = NewLoops[OldLoop]; |
| if (!NewLoop) { |
| // Found a new sub-loop. |
| assert(*BB == OldLoop->getHeader() && |
| "Header should be first in RPO"); |
| |
| Loop *NewLoopParent = NewLoops.lookup(OldLoop->getParentLoop()); |
| assert(NewLoopParent && |
| "Expected parent loop before sub-loop in RPO"); |
| NewLoop = new Loop; |
| NewLoopParent->addChildLoop(NewLoop); |
| |
| // Forget the old loop, since its inputs may have changed. |
| if (SE) |
| SE->forgetLoop(OldLoop); |
| } |
| NewLoop->addBasicBlockToLoop(New, *LI); |
| } |
| |
| 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); |
| } |
| |
| // 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; |
| NeedConditional = false; |
| } |
| |
| // If we know the trip count or a multiple of it, we can safely use an |
| // unconditional branch for some iterations. |
| if (j != BreakoutTrip && (TripMultiple == 0 || j % TripMultiple != 0)) { |
| 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 could register any cloned assumptions instead of clearing the |
| // whole function's cache. |
| AC->clear(); |
| |
| // 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 |
| DEBUG(DT->verifyDomTree()); |
| |
| // Simplify any new induction variables in the partially unrolled loop. |
| if (SE && !CompletelyUnroll) { |
| 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 (isInstructionTriviallyDead(Inst)) |
| BB->getInstList().erase(Inst); |
| else if (Value *V = SimplifyInstruction(Inst, DL)) |
| if (LI->replacementPreservesLCSSAForm(Inst, V)) { |
| Inst->replaceAllUsesWith(V); |
| BB->getInstList().erase(Inst); |
| } |
| } |
| |
| 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) { |
| 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."); |
| } |
| } |
| |
| 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; |
| } |
