| //===-- UnrollLoop.cpp - Loop unrolling utilities -------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // 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/ADT/ArrayRef.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/Optional.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/SetVector.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/StringRef.h" |
| #include "llvm/ADT/Twine.h" |
| #include "llvm/ADT/ilist_iterator.h" |
| #include "llvm/ADT/iterator_range.h" |
| #include "llvm/Analysis/AssumptionCache.h" |
| #include "llvm/Analysis/DomTreeUpdater.h" |
| #include "llvm/Analysis/InstructionSimplify.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/LoopIterator.h" |
| #include "llvm/Analysis/OptimizationRemarkEmitter.h" |
| #include "llvm/Analysis/ScalarEvolution.h" |
| #include "llvm/IR/BasicBlock.h" |
| #include "llvm/IR/CFG.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DebugInfoMetadata.h" |
| #include "llvm/IR/DebugLoc.h" |
| #include "llvm/IR/DiagnosticInfo.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/Instruction.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/IR/Metadata.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/IR/Use.h" |
| #include "llvm/IR/User.h" |
| #include "llvm/IR/ValueHandle.h" |
| #include "llvm/IR/ValueMap.h" |
| #include "llvm/Support/Casting.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/GenericDomTree.h" |
| #include "llvm/Support/MathExtras.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/LoopPeel.h" |
| #include "llvm/Transforms/Utils/LoopSimplify.h" |
| #include "llvm/Transforms/Utils/LoopUtils.h" |
| #include "llvm/Transforms/Utils/SimplifyIndVar.h" |
| #include "llvm/Transforms/Utils/UnrollLoop.h" |
| #include "llvm/Transforms/Utils/ValueMapper.h" |
| #include <algorithm> |
| #include <assert.h> |
| #include <type_traits> |
| #include <vector> |
| |
| namespace llvm { |
| class DataLayout; |
| class Value; |
| } // namespace llvm |
| |
| 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)"); |
| STATISTIC(NumUnrolledNotLatch, "Number of loops unrolled without a conditional " |
| "latch (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.")); |
| |
| static cl::opt<bool> |
| UnrollVerifyDomtree("unroll-verify-domtree", cl::Hidden, |
| cl::desc("Verify domtree after unrolling"), |
| #ifdef EXPENSIVE_CHECKS |
| cl::init(true) |
| #else |
| cl::init(false) |
| #endif |
| ); |
| |
| /// 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, |
| const 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 (const 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 = LI->AllocateLoop(); |
| 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; |
| } |
| } |
| |
| /// The function chooses which type of unroll (epilog or prolog) is more |
| /// profitabale. |
| /// Epilog unroll is more profitable when there is PHI that starts from |
| /// constant. In this case epilog will leave PHI start from constant, |
| /// but prolog will convert it to non-constant. |
| /// |
| /// loop: |
| /// PN = PHI [I, Latch], [CI, PreHeader] |
| /// I = foo(PN) |
| /// ... |
| /// |
| /// Epilog unroll case. |
| /// loop: |
| /// PN = PHI [I2, Latch], [CI, PreHeader] |
| /// I1 = foo(PN) |
| /// I2 = foo(I1) |
| /// ... |
| /// Prolog unroll case. |
| /// NewPN = PHI [PrologI, Prolog], [CI, PreHeader] |
| /// loop: |
| /// PN = PHI [I2, Latch], [NewPN, PreHeader] |
| /// I1 = foo(PN) |
| /// I2 = foo(I1) |
| /// ... |
| /// |
| static bool isEpilogProfitable(Loop *L) { |
| BasicBlock *PreHeader = L->getLoopPreheader(); |
| BasicBlock *Header = L->getHeader(); |
| assert(PreHeader && Header); |
| for (const PHINode &PN : Header->phis()) { |
| if (isa<ConstantInt>(PN.getIncomingValueForBlock(PreHeader))) |
| return true; |
| } |
| return false; |
| } |
| |
| /// Perform some cleanup and simplifications on loops after unrolling. It is |
| /// useful to simplify the IV's in the new loop, as well as do a quick |
| /// simplify/dce pass of the instructions. |
| void llvm::simplifyLoopAfterUnroll(Loop *L, bool SimplifyIVs, LoopInfo *LI, |
| ScalarEvolution *SE, DominatorTree *DT, |
| AssumptionCache *AC, |
| const TargetTransformInfo *TTI) { |
| // Simplify any new induction variables in the partially unrolled loop. |
| if (SE && SimplifyIVs) { |
| SmallVector<WeakTrackingVH, 16> DeadInsts; |
| simplifyLoopIVs(L, SE, DT, LI, TTI, DeadInsts); |
| |
| // Aggressively clean up dead instructions that simplifyLoopIVs already |
| // identified. Any remaining should be cleaned up below. |
| while (!DeadInsts.empty()) { |
| Value *V = DeadInsts.pop_back_val(); |
| if (Instruction *Inst = dyn_cast_or_null<Instruction>(V)) |
| 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 = L->getHeader()->getModule()->getDataLayout(); |
| for (BasicBlock *BB : L->getBlocks()) { |
| for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) { |
| Instruction *Inst = &*I++; |
| |
| if (Value *V = SimplifyInstruction(Inst, {DL, nullptr, DT, AC})) |
| 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. |
| } |
| |
| /// Unroll the given loop by Count. The loop must be in LCSSA form. 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. |
| /// |
| /// If RemainderLoop is non-null, it will receive the remainder loop (if |
| /// required and not fully unrolled). |
| LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI, |
| ScalarEvolution *SE, DominatorTree *DT, |
| AssumptionCache *AC, |
| const TargetTransformInfo *TTI, |
| OptimizationRemarkEmitter *ORE, |
| bool PreserveLCSSA, Loop **RemainderLoop) { |
| |
| if (!L->getLoopPreheader()) { |
| LLVM_DEBUG(dbgs() << " Can't unroll; loop preheader-insertion failed.\n"); |
| return LoopUnrollResult::Unmodified; |
| } |
| |
| if (!L->getLoopLatch()) { |
| LLVM_DEBUG(dbgs() << " Can't unroll; loop exit-block-insertion failed.\n"); |
| return LoopUnrollResult::Unmodified; |
| } |
| |
| // Loops with indirectbr cannot be cloned. |
| if (!L->isSafeToClone()) { |
| LLVM_DEBUG(dbgs() << " Can't unroll; Loop body cannot be cloned.\n"); |
| return LoopUnrollResult::Unmodified; |
| } |
| |
| if (L->getHeader()->hasAddressTaken()) { |
| // The loop-rotate pass can be helpful to avoid this in many cases. |
| LLVM_DEBUG( |
| dbgs() << " Won't unroll loop: address of header block is taken.\n"); |
| return LoopUnrollResult::Unmodified; |
| } |
| |
| if (ULO.TripCount != 0) |
| LLVM_DEBUG(dbgs() << " Trip Count = " << ULO.TripCount << "\n"); |
| if (ULO.TripMultiple != 1) |
| LLVM_DEBUG(dbgs() << " Trip Multiple = " << ULO.TripMultiple << "\n"); |
| |
| // Effectively "DCE" unrolled iterations that are beyond the tripcount |
| // and will never be executed. |
| if (ULO.TripCount != 0 && ULO.Count > ULO.TripCount) |
| ULO.Count = ULO.TripCount; |
| |
| // Don't enter the unroll code if there is nothing to do. |
| if (ULO.TripCount == 0 && ULO.Count < 2 && ULO.PeelCount == 0) { |
| LLVM_DEBUG(dbgs() << "Won't unroll; almost nothing to do\n"); |
| return LoopUnrollResult::Unmodified; |
| } |
| |
| assert(ULO.Count > 0); |
| assert(ULO.TripMultiple > 0); |
| assert(ULO.TripCount == 0 || ULO.TripCount % ULO.TripMultiple == 0); |
| |
| // Are we eliminating the loop control altogether? |
| bool CompletelyUnroll = ULO.Count == ULO.TripCount; |
| |
| // 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 = |
| (ULO.TripCount == 0 && ULO.Count > 0 && ULO.AllowRuntime); |
| |
| assert((!RuntimeTripCount || !ULO.PeelCount) && |
| "Did not expect runtime trip-count unrolling " |
| "and peeling for the same loop"); |
| |
| bool Peeled = false; |
| if (ULO.PeelCount) { |
| Peeled = peelLoop(L, ULO.PeelCount, LI, SE, DT, AC, PreserveLCSSA); |
| |
| // Successful peeling may result in a change in the loop preheader/trip |
| // counts. If we later unroll the loop, we want these to be updated. |
| if (Peeled) { |
| // According to our guards and profitability checks the only |
| // meaningful exit should be latch block. Other exits go to deopt, |
| // so we do not worry about them. |
| BasicBlock *ExitingBlock = L->getLoopLatch(); |
| assert(ExitingBlock && "Loop without exiting block?"); |
| assert(L->isLoopExiting(ExitingBlock) && "Latch is not exiting?"); |
| ULO.TripCount = SE->getSmallConstantTripCount(L, ExitingBlock); |
| ULO.TripMultiple = SE->getSmallConstantTripMultiple(L, ExitingBlock); |
| } |
| } |
| |
| // All these values should be taken only after peeling because they might have |
| // changed. |
| BasicBlock *Preheader = L->getLoopPreheader(); |
| BasicBlock *Header = L->getHeader(); |
| BasicBlock *LatchBlock = L->getLoopLatch(); |
| 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()); }); |
| |
| // The current loop unroll pass can unroll loops that have |
| // (1) single latch; and |
| // (2a) latch is unconditional; or |
| // (2b) latch is conditional and is an exiting block |
| // FIXME: The implementation can be extended to work with more complicated |
| // cases, e.g. loops with multiple latches. |
| BranchInst *LatchBI = dyn_cast<BranchInst>(LatchBlock->getTerminator()); |
| |
| // A conditional branch which exits the loop, which can be optimized to an |
| // unconditional branch in the unrolled loop in some cases. |
| BranchInst *ExitingBI = nullptr; |
| bool LatchIsExiting = L->isLoopExiting(LatchBlock); |
| if (LatchIsExiting) |
| ExitingBI = LatchBI; |
| else if (BasicBlock *ExitingBlock = L->getExitingBlock()) |
| ExitingBI = dyn_cast<BranchInst>(ExitingBlock->getTerminator()); |
| if (!LatchBI || (LatchBI->isConditional() && !LatchIsExiting)) { |
| // If the peeling guard is changed this assert may be relaxed or even |
| // deleted. |
| assert(!Peeled && "Peeling guard changed!"); |
| LLVM_DEBUG( |
| dbgs() << "Can't unroll; a conditional latch must exit the loop"); |
| return LoopUnrollResult::Unmodified; |
| } |
| LLVM_DEBUG({ |
| if (ExitingBI) |
| dbgs() << " Exiting Block = " << ExitingBI->getParent()->getName() |
| << "\n"; |
| else |
| dbgs() << " No single exiting block\n"; |
| }); |
| |
| // Loops containing convergent instructions must have a count that divides |
| // their TripMultiple. |
| LLVM_DEBUG( |
| { |
| bool HasConvergent = false; |
| for (auto &BB : L->blocks()) |
| for (auto &I : *BB) |
| if (auto *CB = dyn_cast<CallBase>(&I)) |
| HasConvergent |= CB->isConvergent(); |
| assert((!HasConvergent || ULO.TripMultiple % ULO.Count == 0) && |
| "Unroll count must divide trip multiple if loop contains a " |
| "convergent operation."); |
| }); |
| |
| bool EpilogProfitability = |
| UnrollRuntimeEpilog.getNumOccurrences() ? UnrollRuntimeEpilog |
| : isEpilogProfitable(L); |
| |
| if (RuntimeTripCount && ULO.TripMultiple % ULO.Count != 0 && |
| !UnrollRuntimeLoopRemainder(L, ULO.Count, ULO.AllowExpensiveTripCount, |
| EpilogProfitability, ULO.UnrollRemainder, |
| ULO.ForgetAllSCEV, LI, SE, DT, AC, TTI, |
| PreserveLCSSA, RemainderLoop)) { |
| if (ULO.Force) |
| RuntimeTripCount = false; |
| else { |
| LLVM_DEBUG(dbgs() << "Won't unroll; remainder loop could not be " |
| "generated when assuming runtime trip count\n"); |
| return LoopUnrollResult::Unmodified; |
| } |
| } |
| |
| // If we know the trip count, we know the multiple... |
| unsigned BreakoutTrip = 0; |
| if (ULO.TripCount != 0) { |
| BreakoutTrip = ULO.TripCount % ULO.Count; |
| ULO.TripMultiple = 0; |
| } else { |
| // Figure out what multiple to use. |
| BreakoutTrip = ULO.TripMultiple = |
| (unsigned)GreatestCommonDivisor64(ULO.Count, ULO.TripMultiple); |
| } |
| |
| using namespace ore; |
| // Report the unrolling decision. |
| if (CompletelyUnroll) { |
| LLVM_DEBUG(dbgs() << "COMPLETELY UNROLLING loop %" << Header->getName() |
| << " with trip count " << ULO.TripCount << "!\n"); |
| if (ORE) |
| ORE->emit([&]() { |
| return OptimizationRemark(DEBUG_TYPE, "FullyUnrolled", L->getStartLoc(), |
| L->getHeader()) |
| << "completely unrolled loop with " |
| << NV("UnrollCount", ULO.TripCount) << " iterations"; |
| }); |
| } else if (ULO.PeelCount) { |
| LLVM_DEBUG(dbgs() << "PEELING loop %" << Header->getName() |
| << " with iteration count " << ULO.PeelCount << "!\n"); |
| if (ORE) |
| ORE->emit([&]() { |
| return OptimizationRemark(DEBUG_TYPE, "Peeled", L->getStartLoc(), |
| L->getHeader()) |
| << " peeled loop by " << NV("PeelCount", ULO.PeelCount) |
| << " iterations"; |
| }); |
| } else { |
| auto DiagBuilder = [&]() { |
| OptimizationRemark Diag(DEBUG_TYPE, "PartialUnrolled", L->getStartLoc(), |
| L->getHeader()); |
| return Diag << "unrolled loop by a factor of " |
| << NV("UnrollCount", ULO.Count); |
| }; |
| |
| LLVM_DEBUG(dbgs() << "UNROLLING loop %" << Header->getName() << " by " |
| << ULO.Count); |
| if (ULO.TripMultiple == 0 || BreakoutTrip != ULO.TripMultiple) { |
| LLVM_DEBUG(dbgs() << " with a breakout at trip " << BreakoutTrip); |
| if (ORE) |
| ORE->emit([&]() { |
| return DiagBuilder() << " with a breakout at trip " |
| << NV("BreakoutTrip", BreakoutTrip); |
| }); |
| } else if (ULO.TripMultiple != 1) { |
| LLVM_DEBUG(dbgs() << " with " << ULO.TripMultiple << " trips per branch"); |
| if (ORE) |
| ORE->emit([&]() { |
| return DiagBuilder() |
| << " with " << NV("TripMultiple", ULO.TripMultiple) |
| << " trips per branch"; |
| }); |
| } else if (RuntimeTripCount) { |
| LLVM_DEBUG(dbgs() << " with run-time trip count"); |
| if (ORE) |
| ORE->emit( |
| [&]() { return DiagBuilder() << " with run-time trip count"; }); |
| } |
| LLVM_DEBUG(dbgs() << "!\n"); |
| } |
| |
| // We are going to make changes to this loop. SCEV may be keeping cached info |
| // about it, in particular about backedge taken count. The changes we make |
| // are guaranteed to invalidate this information for our loop. It is tempting |
| // to only invalidate the loop being unrolled, but it is incorrect as long as |
| // all exiting branches from all inner loops have impact on the outer loops, |
| // and if something changes inside them then any of outer loops may also |
| // change. When we forget outermost loop, we also forget all contained loops |
| // and this is what we need here. |
| if (SE) { |
| if (ULO.ForgetAllSCEV) |
| SE->forgetAllLoops(); |
| else |
| SE->forgetTopmostLoop(L); |
| } |
| |
| if (!LatchIsExiting) |
| ++NumUnrolledNotLatch; |
| Optional<bool> ContinueOnTrue = None; |
| BasicBlock *LoopExit = nullptr; |
| if (ExitingBI) { |
| ContinueOnTrue = L->contains(ExitingBI->getSuccessor(0)); |
| LoopExit = ExitingBI->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 *> ExitingBlocks; |
| std::vector<BasicBlock *> ExitingSucc; |
| std::vector<BasicBlock *> Latches; |
| Headers.push_back(Header); |
| Latches.push_back(LatchBlock); |
| if (ExitingBI) { |
| ExitingBlocks.push_back(ExitingBI->getParent()); |
| ExitingSucc.push_back(ExitingBI->getSuccessor(!(*ContinueOnTrue))); |
| } |
| |
| // 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); |
| |
| if (Header->getParent()->isDebugInfoForProfiling()) |
| for (BasicBlock *BB : L->getBlocks()) |
| for (Instruction &I : *BB) |
| if (!isa<DbgInfoIntrinsic>(&I)) |
| if (const DILocation *DIL = I.getDebugLoc()) { |
| auto NewDIL = DIL->cloneByMultiplyingDuplicationFactor(ULO.Count); |
| if (NewDIL) |
| I.setDebugLoc(NewDIL.getValue()); |
| else |
| LLVM_DEBUG(dbgs() |
| << "Failed to create new discriminator: " |
| << DIL->getFilename() << " Line: " << DIL->getLine()); |
| } |
| |
| // Identify what noalias metadata is inside the loop: if it is inside the |
| // loop, the associated metadata must be cloned for each iteration. |
| SmallVector<MDNode *, 6> LoopLocalNoAliasDeclScopes; |
| identifyNoAliasScopesToClone(L->getBlocks(), LoopLocalNoAliasDeclScopes); |
| |
| for (unsigned It = 1; It != ULO.Count; ++It) { |
| SmallVector<BasicBlock *, 8> 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); |
| |
| assert((*BB != Header || LI->getLoopFor(*BB) == L) && |
| "Header should not be in a sub-loop"); |
| // Tell LI about New. |
| const Loop *OldLoop = addClonedBlockToLoopInfo(*BB, New, LI, NewLoops); |
| if (OldLoop) |
| LoopsToSimplify.insert(NewLoops[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 (PHINode &PHI : Succ->phis()) { |
| 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); |
| |
| // Keep track of the exiting block and its successor block contained in |
| // the loop for the current iteration. |
| if (ExitingBI) { |
| if (*BB == ExitingBlocks[0]) |
| ExitingBlocks.push_back(New); |
| if (*BB == ExitingSucc[0]) |
| ExitingSucc.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 |
| remapInstructionsInBlocks(NewBlocks, LastValueMap); |
| for (BasicBlock *NewBlock : NewBlocks) |
| for (Instruction &I : *NewBlock) |
| if (auto *II = dyn_cast<AssumeInst>(&I)) |
| AC->registerAssumption(II); |
| |
| { |
| // Identify what other metadata depends on the cloned version. After |
| // cloning, replace the metadata with the corrected version for both |
| // memory instructions and noalias intrinsics. |
| std::string ext = (Twine("It") + Twine(It)).str(); |
| cloneAndAdaptNoAliasScopes(LoopLocalNoAliasDeclScopes, NewBlocks, |
| Header->getContext(), ext); |
| } |
| } |
| |
| // 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 (ULO.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()); |
| } |
| } |
| |
| auto setDest = [](BasicBlock *Src, BasicBlock *Dest, BasicBlock *BlockInLoop, |
| bool NeedConditional, Optional<bool> ContinueOnTrue, |
| bool IsDestLoopExit) { |
| auto *Term = cast<BranchInst>(Src->getTerminator()); |
| if (NeedConditional) { |
| // Update the conditional branch's successor for the following |
| // iteration. |
| assert(ContinueOnTrue.hasValue() && |
| "Expecting valid ContinueOnTrue when NeedConditional is true"); |
| Term->setSuccessor(!(*ContinueOnTrue), Dest); |
| } else { |
| // Remove phi operands at this loop exit |
| if (!IsDestLoopExit) { |
| BasicBlock *BB = Src; |
| for (BasicBlock *Succ : successors(BB)) { |
| // Preserve the incoming value from BB if we are jumping to the block |
| // in the current loop. |
| if (Succ == BlockInLoop) |
| continue; |
| for (PHINode &Phi : Succ->phis()) |
| Phi.removeIncomingValue(BB, false); |
| } |
| } |
| // Replace the conditional branch with an unconditional one. |
| BranchInst::Create(Dest, Term); |
| Term->eraseFromParent(); |
| } |
| }; |
| |
| // Connect latches of the unrolled iterations to the headers of the next |
| // iteration. If the latch is also the exiting block, the conditional branch |
| // may have to be preserved. |
| for (unsigned i = 0, e = Latches.size(); i != e; ++i) { |
| // The branch destination. |
| unsigned j = (i + 1) % e; |
| BasicBlock *Dest = Headers[j]; |
| bool NeedConditional = LatchIsExiting; |
| |
| if (LatchIsExiting) { |
| 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 = |
| (ULO.PreserveCondBr && j && !(ULO.PreserveOnlyFirst && i != 0)); |
| } else if (j != BreakoutTrip && |
| (ULO.TripMultiple == 0 || j % ULO.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; |
| } |
| } |
| |
| setDest(Latches[i], Dest, Headers[i], NeedConditional, ContinueOnTrue, |
| Dest == LoopExit); |
| } |
| |
| if (!LatchIsExiting) { |
| // If the latch is not exiting, we may be able to simplify the conditional |
| // branches in the unrolled exiting blocks. |
| for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) { |
| // The branch destination. |
| unsigned j = (i + 1) % e; |
| bool NeedConditional = true; |
| |
| if (RuntimeTripCount && j != 0) |
| NeedConditional = false; |
| |
| if (CompletelyUnroll) |
| // We cannot drop the conditional branch for the last condition, as we |
| // may have to execute the loop body depending on the condition. |
| NeedConditional = j == 0 || ULO.PreserveCondBr; |
| else if (j != BreakoutTrip && |
| (ULO.TripMultiple == 0 || j % ULO.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; |
| |
| // Conditional branches from non-latch exiting block have successors |
| // either in the same loop iteration or outside the loop. The branches are |
| // already correct. |
| if (NeedConditional) |
| continue; |
| setDest(ExitingBlocks[i], ExitingSucc[i], ExitingSucc[i], NeedConditional, |
| None, false); |
| } |
| |
| // When completely unrolling, the last latch becomes unreachable. |
| if (CompletelyUnroll) { |
| BranchInst *Term = cast<BranchInst>(Latches.back()->getTerminator()); |
| new UnreachableInst(Term->getContext(), 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. |
| if (DT && ULO.Count > 1) { |
| for (auto *BB : OriginalLoopBlocks) { |
| auto *BBDomNode = DT->getNode(BB); |
| SmallVector<BasicBlock *, 16> ChildrenToUpdate; |
| for (auto *ChildDomNode : BBDomNode->children()) { |
| auto *ChildBB = ChildDomNode->getBlock(); |
| if (!L->contains(ChildBB)) |
| ChildrenToUpdate.push_back(ChildBB); |
| } |
| BasicBlock *NewIDom; |
| if (ExitingBI && BB == ExitingBlocks[0]) { |
| // The latch is special because we emit unconditional branches in |
| // some cases where the original loop contained a conditional branch. |
| // Since the latch is always at the bottom of the loop, if the latch |
| // dominated an exit before unrolling, the new dominator of that exit |
| // must also be a latch. Specifically, the dominator is the first |
| // latch which ends in a conditional branch, or the last latch if |
| // there is no such latch. |
| // For loops exiting from non latch exiting block, we limit the |
| // branch simplification to single exiting block loops. |
| NewIDom = ExitingBlocks.back(); |
| for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) { |
| Instruction *Term = ExitingBlocks[i]->getTerminator(); |
| if (isa<BranchInst>(Term) && cast<BranchInst>(Term)->isConditional()) { |
| NewIDom = |
| DT->findNearestCommonDominator(ExitingBlocks[i], Latches[i]); |
| break; |
| } |
| } |
| } else { |
| // The new idom of the block will be the nearest 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. |
| NewIDom = DT->findNearestCommonDominator(BB, LatchBlock); |
| } |
| for (auto *ChildBB : ChildrenToUpdate) |
| DT->changeImmediateDominator(ChildBB, NewIDom); |
| } |
| } |
| |
| assert(!DT || !UnrollVerifyDomtree || |
| DT->verify(DominatorTree::VerificationLevel::Fast)); |
| |
| DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy); |
| // Merge adjacent basic blocks, if possible. |
| for (BasicBlock *Latch : Latches) { |
| BranchInst *Term = dyn_cast<BranchInst>(Latch->getTerminator()); |
| assert((Term || |
| (CompletelyUnroll && !LatchIsExiting && Latch == Latches.back())) && |
| "Need a branch as terminator, except when fully unrolling with " |
| "unconditional latch"); |
| if (Term && Term->isUnconditional()) { |
| BasicBlock *Dest = Term->getSuccessor(0); |
| BasicBlock *Fold = Dest->getUniquePredecessor(); |
| if (MergeBlockIntoPredecessor(Dest, &DTU, LI)) { |
| // Dest has been folded into Fold. Update our worklists accordingly. |
| std::replace(Latches.begin(), Latches.end(), Dest, Fold); |
| llvm::erase_value(UnrolledLoopBlocks, Dest); |
| } |
| } |
| } |
| // Apply updates to the DomTree. |
| DT = &DTU.getDomTree(); |
| |
| // At this point, the code is well formed. We now simplify the unrolled loop, |
| // doing constant propagation and dead code elimination as we go. |
| simplifyLoopAfterUnroll(L, !CompletelyUnroll && (ULO.Count > 1 || Peeled), LI, |
| SE, DT, AC, TTI); |
| |
| NumCompletelyUnrolled += CompletelyUnroll; |
| ++NumUnrolled; |
| |
| Loop *OuterL = L->getParentLoop(); |
| // Update LoopInfo if the loop is completely removed. |
| if (CompletelyUnroll) |
| LI->erase(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) { |
| // 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). |
| if (NeedToFixLCSSA) { |
| // 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 LoopInfo::erase. |
| Loop *LatchLoop = LI->getLoopFor(Latches.back()); |
| Loop *FixLCSSALoop = OuterL; |
| if (!FixLCSSALoop->contains(LatchLoop)) |
| while (FixLCSSALoop->getParentLoop() != LatchLoop) |
| FixLCSSALoop = FixLCSSALoop->getParentLoop(); |
| |
| formLCSSARecursively(*FixLCSSALoop, *DT, LI, SE); |
| } else if (PreserveLCSSA) { |
| assert(OuterL->isLCSSAForm(*DT) && |
| "Loops should be in LCSSA form after loop-unroll."); |
| } |
| |
| // TODO: That potentially might be compile-time expensive. We should try |
| // to fix the loop-simplified form incrementally. |
| simplifyLoop(OuterL, DT, LI, SE, AC, nullptr, PreserveLCSSA); |
| } else { |
| // Simplify loops for which we might've broken loop-simplify form. |
| for (Loop *SubLoop : LoopsToSimplify) |
| simplifyLoop(SubLoop, DT, LI, SE, AC, nullptr, PreserveLCSSA); |
| } |
| } |
| |
| return CompletelyUnroll ? LoopUnrollResult::FullyUnrolled |
| : LoopUnrollResult::PartiallyUnrolled; |
| } |
| |
| /// 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; |
| } |
