| //===-- LoopUnrollAndJam.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 loop unroll and jam as a routine, much like | |
| // LoopUnroll.cpp implements loop unroll. | |
| // | |
| //===----------------------------------------------------------------------===// | |
| #include "llvm/ADT/ArrayRef.h" | |
| #include "llvm/ADT/DenseMap.h" | |
| #include "llvm/ADT/STLExtras.h" | |
| #include "llvm/ADT/SmallPtrSet.h" | |
| #include "llvm/ADT/SmallVector.h" | |
| #include "llvm/ADT/Statistic.h" | |
| #include "llvm/ADT/StringRef.h" | |
| #include "llvm/ADT/Twine.h" | |
| #include "llvm/ADT/iterator_range.h" | |
| #include "llvm/Analysis/AssumptionCache.h" | |
| #include "llvm/Analysis/DependenceAnalysis.h" | |
| #include "llvm/Analysis/DomTreeUpdater.h" | |
| #include "llvm/Analysis/LoopInfo.h" | |
| #include "llvm/Analysis/LoopIterator.h" | |
| #include "llvm/Analysis/MustExecute.h" | |
| #include "llvm/Analysis/OptimizationRemarkEmitter.h" | |
| #include "llvm/Analysis/ScalarEvolution.h" | |
| #include "llvm/IR/BasicBlock.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/User.h" | |
| #include "llvm/IR/Value.h" | |
| #include "llvm/IR/ValueHandle.h" | |
| #include "llvm/IR/ValueMap.h" | |
| #include "llvm/Support/Casting.h" | |
| #include "llvm/Support/Debug.h" | |
| #include "llvm/Support/ErrorHandling.h" | |
| #include "llvm/Support/GenericDomTree.h" | |
| #include "llvm/Support/raw_ostream.h" | |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" | |
| #include "llvm/Transforms/Utils/Cloning.h" | |
| #include "llvm/Transforms/Utils/LoopUtils.h" | |
| #include "llvm/Transforms/Utils/UnrollLoop.h" | |
| #include "llvm/Transforms/Utils/ValueMapper.h" | |
| #include <assert.h> | |
| #include <memory> | |
| #include <type_traits> | |
| #include <vector> | |
| using namespace llvm; | |
| #define DEBUG_TYPE "loop-unroll-and-jam" | |
| STATISTIC(NumUnrolledAndJammed, "Number of loops unroll and jammed"); | |
| STATISTIC(NumCompletelyUnrolledAndJammed, "Number of loops unroll and jammed"); | |
| typedef SmallPtrSet<BasicBlock *, 4> BasicBlockSet; | |
| // Partition blocks in an outer/inner loop pair into blocks before and after | |
| // the loop | |
| static bool partitionLoopBlocks(Loop &L, BasicBlockSet &ForeBlocks, | |
| BasicBlockSet &AftBlocks, DominatorTree &DT) { | |
| Loop *SubLoop = L.getSubLoops()[0]; | |
| BasicBlock *SubLoopLatch = SubLoop->getLoopLatch(); | |
| for (BasicBlock *BB : L.blocks()) { | |
| if (!SubLoop->contains(BB)) { | |
| if (DT.dominates(SubLoopLatch, BB)) | |
| AftBlocks.insert(BB); | |
| else | |
| ForeBlocks.insert(BB); | |
| } | |
| } | |
| // Check that all blocks in ForeBlocks together dominate the subloop | |
| // TODO: This might ideally be done better with a dominator/postdominators. | |
| BasicBlock *SubLoopPreHeader = SubLoop->getLoopPreheader(); | |
| for (BasicBlock *BB : ForeBlocks) { | |
| if (BB == SubLoopPreHeader) | |
| continue; | |
| Instruction *TI = BB->getTerminator(); | |
| for (BasicBlock *Succ : successors(TI)) | |
| if (!ForeBlocks.count(Succ)) | |
| return false; | |
| } | |
| return true; | |
| } | |
| /// Partition blocks in a loop nest into blocks before and after each inner | |
| /// loop. | |
| static bool partitionOuterLoopBlocks( | |
| Loop &Root, Loop &JamLoop, BasicBlockSet &JamLoopBlocks, | |
| DenseMap<Loop *, BasicBlockSet> &ForeBlocksMap, | |
| DenseMap<Loop *, BasicBlockSet> &AftBlocksMap, DominatorTree &DT) { | |
| JamLoopBlocks.insert(JamLoop.block_begin(), JamLoop.block_end()); | |
| for (Loop *L : Root.getLoopsInPreorder()) { | |
| if (L == &JamLoop) | |
| break; | |
| if (!partitionLoopBlocks(*L, ForeBlocksMap[L], AftBlocksMap[L], DT)) | |
| return false; | |
| } | |
| return true; | |
| } | |
| // TODO Remove when UnrollAndJamLoop changed to support unroll and jamming more | |
| // than 2 levels loop. | |
| static bool partitionOuterLoopBlocks(Loop *L, Loop *SubLoop, | |
| BasicBlockSet &ForeBlocks, | |
| BasicBlockSet &SubLoopBlocks, | |
| BasicBlockSet &AftBlocks, | |
| DominatorTree *DT) { | |
| SubLoopBlocks.insert(SubLoop->block_begin(), SubLoop->block_end()); | |
| return partitionLoopBlocks(*L, ForeBlocks, AftBlocks, *DT); | |
| } | |
| // Looks at the phi nodes in Header for values coming from Latch. For these | |
| // instructions and all their operands calls Visit on them, keeping going for | |
| // all the operands in AftBlocks. Returns false if Visit returns false, | |
| // otherwise returns true. This is used to process the instructions in the | |
| // Aft blocks that need to be moved before the subloop. It is used in two | |
| // places. One to check that the required set of instructions can be moved | |
| // before the loop. Then to collect the instructions to actually move in | |
| // moveHeaderPhiOperandsToForeBlocks. | |
| template <typename T> | |
| static bool processHeaderPhiOperands(BasicBlock *Header, BasicBlock *Latch, | |
| BasicBlockSet &AftBlocks, T Visit) { | |
| SmallPtrSet<Instruction *, 8> VisitedInstr; | |
| std::function<bool(Instruction * I)> ProcessInstr = [&](Instruction *I) { | |
| if (VisitedInstr.count(I)) | |
| return true; | |
| VisitedInstr.insert(I); | |
| if (AftBlocks.count(I->getParent())) | |
| for (auto &U : I->operands()) | |
| if (Instruction *II = dyn_cast<Instruction>(U)) | |
| if (!ProcessInstr(II)) | |
| return false; | |
| return Visit(I); | |
| }; | |
| for (auto &Phi : Header->phis()) { | |
| Value *V = Phi.getIncomingValueForBlock(Latch); | |
| if (Instruction *I = dyn_cast<Instruction>(V)) | |
| if (!ProcessInstr(I)) | |
| return false; | |
| } | |
| return true; | |
| } | |
| // Move the phi operands of Header from Latch out of AftBlocks to InsertLoc. | |
| static void moveHeaderPhiOperandsToForeBlocks(BasicBlock *Header, | |
| BasicBlock *Latch, | |
| Instruction *InsertLoc, | |
| BasicBlockSet &AftBlocks) { | |
| // We need to ensure we move the instructions in the correct order, | |
| // starting with the earliest required instruction and moving forward. | |
| processHeaderPhiOperands(Header, Latch, AftBlocks, | |
| [&AftBlocks, &InsertLoc](Instruction *I) { | |
| if (AftBlocks.count(I->getParent())) | |
| I->moveBefore(InsertLoc); | |
| return true; | |
| }); | |
| } | |
| /* | |
| This method performs Unroll and Jam. For a simple loop like: | |
| for (i = ..) | |
| Fore(i) | |
| for (j = ..) | |
| SubLoop(i, j) | |
| Aft(i) | |
| Instead of doing normal inner or outer unrolling, we do: | |
| for (i = .., i+=2) | |
| Fore(i) | |
| Fore(i+1) | |
| for (j = ..) | |
| SubLoop(i, j) | |
| SubLoop(i+1, j) | |
| Aft(i) | |
| Aft(i+1) | |
| So the outer loop is essetially unrolled and then the inner loops are fused | |
| ("jammed") together into a single loop. This can increase speed when there | |
| are loads in SubLoop that are invariant to i, as they become shared between | |
| the now jammed inner loops. | |
| We do this by spliting the blocks in the loop into Fore, Subloop and Aft. | |
| Fore blocks are those before the inner loop, Aft are those after. Normal | |
| Unroll code is used to copy each of these sets of blocks and the results are | |
| combined together into the final form above. | |
| isSafeToUnrollAndJam should be used prior to calling this to make sure the | |
| unrolling will be valid. Checking profitablility is also advisable. | |
| If EpilogueLoop is non-null, it receives the epilogue loop (if it was | |
| necessary to create one and not fully unrolled). | |
| */ | |
| LoopUnrollResult | |
| llvm::UnrollAndJamLoop(Loop *L, unsigned Count, unsigned TripCount, | |
| unsigned TripMultiple, bool UnrollRemainder, | |
| LoopInfo *LI, ScalarEvolution *SE, DominatorTree *DT, | |
| AssumptionCache *AC, const TargetTransformInfo *TTI, | |
| OptimizationRemarkEmitter *ORE, Loop **EpilogueLoop) { | |
| // When we enter here we should have already checked that it is safe | |
| BasicBlock *Header = L->getHeader(); | |
| assert(Header && "No header."); | |
| assert(L->getSubLoops().size() == 1); | |
| Loop *SubLoop = *L->begin(); | |
| // Don't enter the unroll code if there is nothing to do. | |
| if (TripCount == 0 && Count < 2) { | |
| LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; almost nothing to do\n"); | |
| return LoopUnrollResult::Unmodified; | |
| } | |
| assert(Count > 0); | |
| assert(TripMultiple > 0); | |
| assert(TripCount == 0 || TripCount % TripMultiple == 0); | |
| // Are we eliminating the loop control altogether? | |
| bool CompletelyUnroll = (Count == TripCount); | |
| // We use the runtime remainder in cases where we don't know trip multiple | |
| if (TripMultiple % Count != 0) { | |
| if (!UnrollRuntimeLoopRemainder(L, Count, /*AllowExpensiveTripCount*/ false, | |
| /*UseEpilogRemainder*/ true, | |
| UnrollRemainder, /*ForgetAllSCEV*/ false, | |
| LI, SE, DT, AC, TTI, true, EpilogueLoop)) { | |
| LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; remainder loop could not be " | |
| "generated when assuming runtime trip count\n"); | |
| return LoopUnrollResult::Unmodified; | |
| } | |
| } | |
| // Notify ScalarEvolution that the loop will be substantially changed, | |
| // if not outright eliminated. | |
| if (SE) { | |
| SE->forgetLoop(L); | |
| SE->forgetBlockAndLoopDispositions(); | |
| } | |
| using namespace ore; | |
| // Report the unrolling decision. | |
| if (CompletelyUnroll) { | |
| LLVM_DEBUG(dbgs() << "COMPLETELY UNROLL AND JAMMING loop %" | |
| << Header->getName() << " with trip count " << TripCount | |
| << "!\n"); | |
| ORE->emit(OptimizationRemark(DEBUG_TYPE, "FullyUnrolled", L->getStartLoc(), | |
| L->getHeader()) | |
| << "completely unroll and jammed loop with " | |
| << NV("UnrollCount", TripCount) << " iterations"); | |
| } else { | |
| auto DiagBuilder = [&]() { | |
| OptimizationRemark Diag(DEBUG_TYPE, "PartialUnrolled", L->getStartLoc(), | |
| L->getHeader()); | |
| return Diag << "unroll and jammed loop by a factor of " | |
| << NV("UnrollCount", Count); | |
| }; | |
| LLVM_DEBUG(dbgs() << "UNROLL AND JAMMING loop %" << Header->getName() | |
| << " by " << Count); | |
| if (TripMultiple != 1) { | |
| LLVM_DEBUG(dbgs() << " with " << TripMultiple << " trips per branch"); | |
| ORE->emit([&]() { | |
| return DiagBuilder() << " with " << NV("TripMultiple", TripMultiple) | |
| << " trips per branch"; | |
| }); | |
| } else { | |
| LLVM_DEBUG(dbgs() << " with run-time trip count"); | |
| ORE->emit([&]() { return DiagBuilder() << " with run-time trip count"; }); | |
| } | |
| LLVM_DEBUG(dbgs() << "!\n"); | |
| } | |
| BasicBlock *Preheader = L->getLoopPreheader(); | |
| BasicBlock *LatchBlock = L->getLoopLatch(); | |
| assert(Preheader && "No preheader"); | |
| assert(LatchBlock && "No latch block"); | |
| BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator()); | |
| assert(BI && !BI->isUnconditional()); | |
| bool ContinueOnTrue = L->contains(BI->getSuccessor(0)); | |
| BasicBlock *LoopExit = BI->getSuccessor(ContinueOnTrue); | |
| bool SubLoopContinueOnTrue = SubLoop->contains( | |
| SubLoop->getLoopLatch()->getTerminator()->getSuccessor(0)); | |
| // Partition blocks in an outer/inner loop pair into blocks before and after | |
| // the loop | |
| BasicBlockSet SubLoopBlocks; | |
| BasicBlockSet ForeBlocks; | |
| BasicBlockSet AftBlocks; | |
| partitionOuterLoopBlocks(L, SubLoop, ForeBlocks, SubLoopBlocks, AftBlocks, | |
| DT); | |
| // We keep track of the entering/first and exiting/last block of each of | |
| // Fore/SubLoop/Aft in each iteration. This helps make the stapling up of | |
| // blocks easier. | |
| std::vector<BasicBlock *> ForeBlocksFirst; | |
| std::vector<BasicBlock *> ForeBlocksLast; | |
| std::vector<BasicBlock *> SubLoopBlocksFirst; | |
| std::vector<BasicBlock *> SubLoopBlocksLast; | |
| std::vector<BasicBlock *> AftBlocksFirst; | |
| std::vector<BasicBlock *> AftBlocksLast; | |
| ForeBlocksFirst.push_back(Header); | |
| ForeBlocksLast.push_back(SubLoop->getLoopPreheader()); | |
| SubLoopBlocksFirst.push_back(SubLoop->getHeader()); | |
| SubLoopBlocksLast.push_back(SubLoop->getExitingBlock()); | |
| AftBlocksFirst.push_back(SubLoop->getExitBlock()); | |
| AftBlocksLast.push_back(L->getExitingBlock()); | |
| // Maps Blocks[0] -> Blocks[It] | |
| ValueToValueMapTy LastValueMap; | |
| // Move any instructions from fore phi operands from AftBlocks into Fore. | |
| moveHeaderPhiOperandsToForeBlocks( | |
| Header, LatchBlock, ForeBlocksLast[0]->getTerminator(), AftBlocks); | |
| // 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(); | |
| // When a FSDiscriminator is enabled, we don't need to add the multiply | |
| // factors to the discriminators. | |
| if (Header->getParent()->shouldEmitDebugInfoForProfiling() && | |
| !EnableFSDiscriminator) | |
| for (BasicBlock *BB : L->getBlocks()) | |
| for (Instruction &I : *BB) | |
| if (!isa<DbgInfoIntrinsic>(&I)) | |
| if (const DILocation *DIL = I.getDebugLoc()) { | |
| auto NewDIL = DIL->cloneByMultiplyingDuplicationFactor(Count); | |
| if (NewDIL) | |
| I.setDebugLoc(*NewDIL); | |
| else | |
| LLVM_DEBUG(dbgs() | |
| << "Failed to create new discriminator: " | |
| << DIL->getFilename() << " Line: " << DIL->getLine()); | |
| } | |
| // Copy all blocks | |
| for (unsigned It = 1; It != Count; ++It) { | |
| SmallVector<BasicBlock *, 8> NewBlocks; | |
| // Maps Blocks[It] -> Blocks[It-1] | |
| DenseMap<Value *, Value *> PrevItValueMap; | |
| SmallDenseMap<const Loop *, Loop *, 4> NewLoops; | |
| NewLoops[L] = L; | |
| NewLoops[SubLoop] = SubLoop; | |
| for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) { | |
| ValueToValueMapTy VMap; | |
| BasicBlock *New = CloneBasicBlock(*BB, VMap, "." + Twine(It)); | |
| Header->getParent()->insert(Header->getParent()->end(), New); | |
| // Tell LI about New. | |
| addClonedBlockToLoopInfo(*BB, New, LI, NewLoops); | |
| if (ForeBlocks.count(*BB)) { | |
| if (*BB == ForeBlocksFirst[0]) | |
| ForeBlocksFirst.push_back(New); | |
| if (*BB == ForeBlocksLast[0]) | |
| ForeBlocksLast.push_back(New); | |
| } else if (SubLoopBlocks.count(*BB)) { | |
| if (*BB == SubLoopBlocksFirst[0]) | |
| SubLoopBlocksFirst.push_back(New); | |
| if (*BB == SubLoopBlocksLast[0]) | |
| SubLoopBlocksLast.push_back(New); | |
| } else if (AftBlocks.count(*BB)) { | |
| if (*BB == AftBlocksFirst[0]) | |
| AftBlocksFirst.push_back(New); | |
| if (*BB == AftBlocksLast[0]) | |
| AftBlocksLast.push_back(New); | |
| } else { | |
| llvm_unreachable("BB being cloned should be in Fore/Sub/Aft"); | |
| } | |
| // Update our running maps of newest clones | |
| PrevItValueMap[New] = (It == 1 ? *BB : LastValueMap[*BB]); | |
| LastValueMap[*BB] = New; | |
| for (ValueToValueMapTy::iterator VI = VMap.begin(), VE = VMap.end(); | |
| VI != VE; ++VI) { | |
| PrevItValueMap[VI->second] = | |
| const_cast<Value *>(It == 1 ? VI->first : LastValueMap[VI->first]); | |
| LastValueMap[VI->first] = VI->second; | |
| } | |
| NewBlocks.push_back(New); | |
| // Update DomTree: | |
| if (*BB == ForeBlocksFirst[0]) | |
| DT->addNewBlock(New, ForeBlocksLast[It - 1]); | |
| else if (*BB == SubLoopBlocksFirst[0]) | |
| DT->addNewBlock(New, SubLoopBlocksLast[It - 1]); | |
| else if (*BB == AftBlocksFirst[0]) | |
| DT->addNewBlock(New, AftBlocksLast[It - 1]); | |
| else { | |
| // Each set of blocks (Fore/Sub/Aft) will have the same internal domtree | |
| // structure. | |
| auto BBDomNode = DT->getNode(*BB); | |
| auto BBIDom = BBDomNode->getIDom(); | |
| BasicBlock *OriginalBBIDom = BBIDom->getBlock(); | |
| assert(OriginalBBIDom); | |
| assert(LastValueMap[cast<Value>(OriginalBBIDom)]); | |
| 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); | |
| } | |
| } | |
| // Alter the ForeBlocks phi's, pointing them at the latest version of the | |
| // value from the previous iteration's phis | |
| for (PHINode &Phi : ForeBlocksFirst[It]->phis()) { | |
| Value *OldValue = Phi.getIncomingValueForBlock(AftBlocksLast[It]); | |
| assert(OldValue && "should have incoming edge from Aft[It]"); | |
| Value *NewValue = OldValue; | |
| if (Value *PrevValue = PrevItValueMap[OldValue]) | |
| NewValue = PrevValue; | |
| assert(Phi.getNumOperands() == 2); | |
| Phi.setIncomingBlock(0, ForeBlocksLast[It - 1]); | |
| Phi.setIncomingValue(0, NewValue); | |
| Phi.removeIncomingValue(1); | |
| } | |
| } | |
| // Now that all the basic blocks for the unrolled iterations are in place, | |
| // finish up connecting the blocks and phi nodes. At this point LastValueMap | |
| // is the last unrolled iterations values. | |
| // Update Phis in BB from OldBB to point to NewBB and use the latest value | |
| // from LastValueMap | |
| auto updatePHIBlocksAndValues = [](BasicBlock *BB, BasicBlock *OldBB, | |
| BasicBlock *NewBB, | |
| ValueToValueMapTy &LastValueMap) { | |
| for (PHINode &Phi : BB->phis()) { | |
| for (unsigned b = 0; b < Phi.getNumIncomingValues(); ++b) { | |
| if (Phi.getIncomingBlock(b) == OldBB) { | |
| Value *OldValue = Phi.getIncomingValue(b); | |
| if (Value *LastValue = LastValueMap[OldValue]) | |
| Phi.setIncomingValue(b, LastValue); | |
| Phi.setIncomingBlock(b, NewBB); | |
| break; | |
| } | |
| } | |
| } | |
| }; | |
| // Move all the phis from Src into Dest | |
| auto movePHIs = [](BasicBlock *Src, BasicBlock *Dest) { | |
| Instruction *insertPoint = Dest->getFirstNonPHI(); | |
| while (PHINode *Phi = dyn_cast<PHINode>(Src->begin())) | |
| Phi->moveBefore(insertPoint); | |
| }; | |
| // Update the PHI values outside the loop to point to the last block | |
| updatePHIBlocksAndValues(LoopExit, AftBlocksLast[0], AftBlocksLast.back(), | |
| LastValueMap); | |
| // Update ForeBlocks successors and phi nodes | |
| BranchInst *ForeTerm = | |
| cast<BranchInst>(ForeBlocksLast.back()->getTerminator()); | |
| assert(ForeTerm->getNumSuccessors() == 1 && "Expecting one successor"); | |
| ForeTerm->setSuccessor(0, SubLoopBlocksFirst[0]); | |
| if (CompletelyUnroll) { | |
| while (PHINode *Phi = dyn_cast<PHINode>(ForeBlocksFirst[0]->begin())) { | |
| Phi->replaceAllUsesWith(Phi->getIncomingValueForBlock(Preheader)); | |
| Phi->eraseFromParent(); | |
| } | |
| } else { | |
| // Update the PHI values to point to the last aft block | |
| updatePHIBlocksAndValues(ForeBlocksFirst[0], AftBlocksLast[0], | |
| AftBlocksLast.back(), LastValueMap); | |
| } | |
| for (unsigned It = 1; It != Count; It++) { | |
| // Remap ForeBlock successors from previous iteration to this | |
| BranchInst *ForeTerm = | |
| cast<BranchInst>(ForeBlocksLast[It - 1]->getTerminator()); | |
| assert(ForeTerm->getNumSuccessors() == 1 && "Expecting one successor"); | |
| ForeTerm->setSuccessor(0, ForeBlocksFirst[It]); | |
| } | |
| // Subloop successors and phis | |
| BranchInst *SubTerm = | |
| cast<BranchInst>(SubLoopBlocksLast.back()->getTerminator()); | |
| SubTerm->setSuccessor(!SubLoopContinueOnTrue, SubLoopBlocksFirst[0]); | |
| SubTerm->setSuccessor(SubLoopContinueOnTrue, AftBlocksFirst[0]); | |
| SubLoopBlocksFirst[0]->replacePhiUsesWith(ForeBlocksLast[0], | |
| ForeBlocksLast.back()); | |
| SubLoopBlocksFirst[0]->replacePhiUsesWith(SubLoopBlocksLast[0], | |
| SubLoopBlocksLast.back()); | |
| for (unsigned It = 1; It != Count; It++) { | |
| // Replace the conditional branch of the previous iteration subloop with an | |
| // unconditional one to this one | |
| BranchInst *SubTerm = | |
| cast<BranchInst>(SubLoopBlocksLast[It - 1]->getTerminator()); | |
| BranchInst::Create(SubLoopBlocksFirst[It], SubTerm); | |
| SubTerm->eraseFromParent(); | |
| SubLoopBlocksFirst[It]->replacePhiUsesWith(ForeBlocksLast[It], | |
| ForeBlocksLast.back()); | |
| SubLoopBlocksFirst[It]->replacePhiUsesWith(SubLoopBlocksLast[It], | |
| SubLoopBlocksLast.back()); | |
| movePHIs(SubLoopBlocksFirst[It], SubLoopBlocksFirst[0]); | |
| } | |
| // Aft blocks successors and phis | |
| BranchInst *AftTerm = cast<BranchInst>(AftBlocksLast.back()->getTerminator()); | |
| if (CompletelyUnroll) { | |
| BranchInst::Create(LoopExit, AftTerm); | |
| AftTerm->eraseFromParent(); | |
| } else { | |
| AftTerm->setSuccessor(!ContinueOnTrue, ForeBlocksFirst[0]); | |
| assert(AftTerm->getSuccessor(ContinueOnTrue) == LoopExit && | |
| "Expecting the ContinueOnTrue successor of AftTerm to be LoopExit"); | |
| } | |
| AftBlocksFirst[0]->replacePhiUsesWith(SubLoopBlocksLast[0], | |
| SubLoopBlocksLast.back()); | |
| for (unsigned It = 1; It != Count; It++) { | |
| // Replace the conditional branch of the previous iteration subloop with an | |
| // unconditional one to this one | |
| BranchInst *AftTerm = | |
| cast<BranchInst>(AftBlocksLast[It - 1]->getTerminator()); | |
| BranchInst::Create(AftBlocksFirst[It], AftTerm); | |
| AftTerm->eraseFromParent(); | |
| AftBlocksFirst[It]->replacePhiUsesWith(SubLoopBlocksLast[It], | |
| SubLoopBlocksLast.back()); | |
| movePHIs(AftBlocksFirst[It], AftBlocksFirst[0]); | |
| } | |
| DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy); | |
| // Dominator Tree. Remove the old links between Fore, Sub and Aft, adding the | |
| // new ones required. | |
| if (Count != 1) { | |
| SmallVector<DominatorTree::UpdateType, 4> DTUpdates; | |
| DTUpdates.emplace_back(DominatorTree::UpdateKind::Delete, ForeBlocksLast[0], | |
| SubLoopBlocksFirst[0]); | |
| DTUpdates.emplace_back(DominatorTree::UpdateKind::Delete, | |
| SubLoopBlocksLast[0], AftBlocksFirst[0]); | |
| DTUpdates.emplace_back(DominatorTree::UpdateKind::Insert, | |
| ForeBlocksLast.back(), SubLoopBlocksFirst[0]); | |
| DTUpdates.emplace_back(DominatorTree::UpdateKind::Insert, | |
| SubLoopBlocksLast.back(), AftBlocksFirst[0]); | |
| DTU.applyUpdatesPermissive(DTUpdates); | |
| } | |
| // Merge adjacent basic blocks, if possible. | |
| SmallPtrSet<BasicBlock *, 16> MergeBlocks; | |
| MergeBlocks.insert(ForeBlocksLast.begin(), ForeBlocksLast.end()); | |
| MergeBlocks.insert(SubLoopBlocksLast.begin(), SubLoopBlocksLast.end()); | |
| MergeBlocks.insert(AftBlocksLast.begin(), AftBlocksLast.end()); | |
| MergeBlockSuccessorsIntoGivenBlocks(MergeBlocks, L, &DTU, LI); | |
| // Apply updates to the DomTree. | |
| DT = &DTU.getDomTree(); | |
| // 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. | |
| simplifyLoopAfterUnroll(SubLoop, true, LI, SE, DT, AC, TTI); | |
| simplifyLoopAfterUnroll(L, !CompletelyUnroll && Count > 1, LI, SE, DT, AC, | |
| TTI); | |
| NumCompletelyUnrolledAndJammed += CompletelyUnroll; | |
| ++NumUnrolledAndJammed; | |
| // Update LoopInfo if the loop is completely removed. | |
| if (CompletelyUnroll) | |
| LI->erase(L); | |
| #ifndef NDEBUG | |
| // We shouldn't have done anything to break loop simplify form or LCSSA. | |
| Loop *OutestLoop = SubLoop->getParentLoop() | |
| ? SubLoop->getParentLoop()->getParentLoop() | |
| ? SubLoop->getParentLoop()->getParentLoop() | |
| : SubLoop->getParentLoop() | |
| : SubLoop; | |
| assert(DT->verify()); | |
| LI->verify(*DT); | |
| assert(OutestLoop->isRecursivelyLCSSAForm(*DT, *LI)); | |
| if (!CompletelyUnroll) | |
| assert(L->isLoopSimplifyForm()); | |
| assert(SubLoop->isLoopSimplifyForm()); | |
| SE->verify(); | |
| #endif | |
| return CompletelyUnroll ? LoopUnrollResult::FullyUnrolled | |
| : LoopUnrollResult::PartiallyUnrolled; | |
| } | |
| static bool getLoadsAndStores(BasicBlockSet &Blocks, | |
| SmallVector<Instruction *, 4> &MemInstr) { | |
| // Scan the BBs and collect legal loads and stores. | |
| // Returns false if non-simple loads/stores are found. | |
| for (BasicBlock *BB : Blocks) { | |
| for (Instruction &I : *BB) { | |
| if (auto *Ld = dyn_cast<LoadInst>(&I)) { | |
| if (!Ld->isSimple()) | |
| return false; | |
| MemInstr.push_back(&I); | |
| } else if (auto *St = dyn_cast<StoreInst>(&I)) { | |
| if (!St->isSimple()) | |
| return false; | |
| MemInstr.push_back(&I); | |
| } else if (I.mayReadOrWriteMemory()) { | |
| return false; | |
| } | |
| } | |
| } | |
| return true; | |
| } | |
| static bool preservesForwardDependence(Instruction *Src, Instruction *Dst, | |
| unsigned UnrollLevel, unsigned JamLevel, | |
| bool Sequentialized, Dependence *D) { | |
| // UnrollLevel might carry the dependency Src --> Dst | |
| // Does a different loop after unrolling? | |
| for (unsigned CurLoopDepth = UnrollLevel + 1; CurLoopDepth <= JamLevel; | |
| ++CurLoopDepth) { | |
| auto JammedDir = D->getDirection(CurLoopDepth); | |
| if (JammedDir == Dependence::DVEntry::LT) | |
| return true; | |
| if (JammedDir & Dependence::DVEntry::GT) | |
| return false; | |
| } | |
| return true; | |
| } | |
| static bool preservesBackwardDependence(Instruction *Src, Instruction *Dst, | |
| unsigned UnrollLevel, unsigned JamLevel, | |
| bool Sequentialized, Dependence *D) { | |
| // UnrollLevel might carry the dependency Dst --> Src | |
| for (unsigned CurLoopDepth = UnrollLevel + 1; CurLoopDepth <= JamLevel; | |
| ++CurLoopDepth) { | |
| auto JammedDir = D->getDirection(CurLoopDepth); | |
| if (JammedDir == Dependence::DVEntry::GT) | |
| return true; | |
| if (JammedDir & Dependence::DVEntry::LT) | |
| return false; | |
| } | |
| // Backward dependencies are only preserved if not interleaved. | |
| return Sequentialized; | |
| } | |
| // Check whether it is semantically safe Src and Dst considering any potential | |
| // dependency between them. | |
| // | |
| // @param UnrollLevel The level of the loop being unrolled | |
| // @param JamLevel The level of the loop being jammed; if Src and Dst are on | |
| // different levels, the outermost common loop counts as jammed level | |
| // | |
| // @return true if is safe and false if there is a dependency violation. | |
| static bool checkDependency(Instruction *Src, Instruction *Dst, | |
| unsigned UnrollLevel, unsigned JamLevel, | |
| bool Sequentialized, DependenceInfo &DI) { | |
| assert(UnrollLevel <= JamLevel && | |
| "Expecting JamLevel to be at least UnrollLevel"); | |
| if (Src == Dst) | |
| return true; | |
| // Ignore Input dependencies. | |
| if (isa<LoadInst>(Src) && isa<LoadInst>(Dst)) | |
| return true; | |
| // Check whether unroll-and-jam may violate a dependency. | |
| // By construction, every dependency will be lexicographically non-negative | |
| // (if it was, it would violate the current execution order), such as | |
| // (0,0,>,*,*) | |
| // Unroll-and-jam changes the GT execution of two executions to the same | |
| // iteration of the chosen unroll level. That is, a GT dependence becomes a GE | |
| // dependence (or EQ, if we fully unrolled the loop) at the loop's position: | |
| // (0,0,>=,*,*) | |
| // Now, the dependency is not necessarily non-negative anymore, i.e. | |
| // unroll-and-jam may violate correctness. | |
| std::unique_ptr<Dependence> D = DI.depends(Src, Dst, true); | |
| if (!D) | |
| return true; | |
| assert(D->isOrdered() && "Expected an output, flow or anti dep."); | |
| if (D->isConfused()) { | |
| LLVM_DEBUG(dbgs() << " Confused dependency between:\n" | |
| << " " << *Src << "\n" | |
| << " " << *Dst << "\n"); | |
| return false; | |
| } | |
| // If outer levels (levels enclosing the loop being unroll-and-jammed) have a | |
| // non-equal direction, then the locations accessed in the inner levels cannot | |
| // overlap in memory. We assumes the indexes never overlap into neighboring | |
| // dimensions. | |
| for (unsigned CurLoopDepth = 1; CurLoopDepth < UnrollLevel; ++CurLoopDepth) | |
| if (!(D->getDirection(CurLoopDepth) & Dependence::DVEntry::EQ)) | |
| return true; | |
| auto UnrollDirection = D->getDirection(UnrollLevel); | |
| // If the distance carried by the unrolled loop is 0, then after unrolling | |
| // that distance will become non-zero resulting in non-overlapping accesses in | |
| // the inner loops. | |
| if (UnrollDirection == Dependence::DVEntry::EQ) | |
| return true; | |
| if (UnrollDirection & Dependence::DVEntry::LT && | |
| !preservesForwardDependence(Src, Dst, UnrollLevel, JamLevel, | |
| Sequentialized, D.get())) | |
| return false; | |
| if (UnrollDirection & Dependence::DVEntry::GT && | |
| !preservesBackwardDependence(Src, Dst, UnrollLevel, JamLevel, | |
| Sequentialized, D.get())) | |
| return false; | |
| return true; | |
| } | |
| static bool | |
| checkDependencies(Loop &Root, const BasicBlockSet &SubLoopBlocks, | |
| const DenseMap<Loop *, BasicBlockSet> &ForeBlocksMap, | |
| const DenseMap<Loop *, BasicBlockSet> &AftBlocksMap, | |
| DependenceInfo &DI, LoopInfo &LI) { | |
| SmallVector<BasicBlockSet, 8> AllBlocks; | |
| for (Loop *L : Root.getLoopsInPreorder()) | |
| if (ForeBlocksMap.find(L) != ForeBlocksMap.end()) | |
| AllBlocks.push_back(ForeBlocksMap.lookup(L)); | |
| AllBlocks.push_back(SubLoopBlocks); | |
| for (Loop *L : Root.getLoopsInPreorder()) | |
| if (AftBlocksMap.find(L) != AftBlocksMap.end()) | |
| AllBlocks.push_back(AftBlocksMap.lookup(L)); | |
| unsigned LoopDepth = Root.getLoopDepth(); | |
| SmallVector<Instruction *, 4> EarlierLoadsAndStores; | |
| SmallVector<Instruction *, 4> CurrentLoadsAndStores; | |
| for (BasicBlockSet &Blocks : AllBlocks) { | |
| CurrentLoadsAndStores.clear(); | |
| if (!getLoadsAndStores(Blocks, CurrentLoadsAndStores)) | |
| return false; | |
| Loop *CurLoop = LI.getLoopFor((*Blocks.begin())->front().getParent()); | |
| unsigned CurLoopDepth = CurLoop->getLoopDepth(); | |
| for (auto *Earlier : EarlierLoadsAndStores) { | |
| Loop *EarlierLoop = LI.getLoopFor(Earlier->getParent()); | |
| unsigned EarlierDepth = EarlierLoop->getLoopDepth(); | |
| unsigned CommonLoopDepth = std::min(EarlierDepth, CurLoopDepth); | |
| for (auto *Later : CurrentLoadsAndStores) { | |
| if (!checkDependency(Earlier, Later, LoopDepth, CommonLoopDepth, false, | |
| DI)) | |
| return false; | |
| } | |
| } | |
| size_t NumInsts = CurrentLoadsAndStores.size(); | |
| for (size_t I = 0; I < NumInsts; ++I) { | |
| for (size_t J = I; J < NumInsts; ++J) { | |
| if (!checkDependency(CurrentLoadsAndStores[I], CurrentLoadsAndStores[J], | |
| LoopDepth, CurLoopDepth, true, DI)) | |
| return false; | |
| } | |
| } | |
| EarlierLoadsAndStores.append(CurrentLoadsAndStores.begin(), | |
| CurrentLoadsAndStores.end()); | |
| } | |
| return true; | |
| } | |
| static bool isEligibleLoopForm(const Loop &Root) { | |
| // Root must have a child. | |
| if (Root.getSubLoops().size() != 1) | |
| return false; | |
| const Loop *L = &Root; | |
| do { | |
| // All loops in Root need to be in simplify and rotated form. | |
| if (!L->isLoopSimplifyForm()) | |
| return false; | |
| if (!L->isRotatedForm()) | |
| return false; | |
| if (L->getHeader()->hasAddressTaken()) { | |
| LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; Address taken\n"); | |
| return false; | |
| } | |
| unsigned SubLoopsSize = L->getSubLoops().size(); | |
| if (SubLoopsSize == 0) | |
| return true; | |
| // Only one child is allowed. | |
| if (SubLoopsSize != 1) | |
| return false; | |
| // Only loops with a single exit block can be unrolled and jammed. | |
| // The function getExitBlock() is used for this check, rather than | |
| // getUniqueExitBlock() to ensure loops with mulitple exit edges are | |
| // disallowed. | |
| if (!L->getExitBlock()) { | |
| LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; only loops with single exit " | |
| "blocks can be unrolled and jammed.\n"); | |
| return false; | |
| } | |
| // Only loops with a single exiting block can be unrolled and jammed. | |
| if (!L->getExitingBlock()) { | |
| LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; only loops with single " | |
| "exiting blocks can be unrolled and jammed.\n"); | |
| return false; | |
| } | |
| L = L->getSubLoops()[0]; | |
| } while (L); | |
| return true; | |
| } | |
| static Loop *getInnerMostLoop(Loop *L) { | |
| while (!L->getSubLoops().empty()) | |
| L = L->getSubLoops()[0]; | |
| return L; | |
| } | |
| bool llvm::isSafeToUnrollAndJam(Loop *L, ScalarEvolution &SE, DominatorTree &DT, | |
| DependenceInfo &DI, LoopInfo &LI) { | |
| if (!isEligibleLoopForm(*L)) { | |
| LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; Ineligible loop form\n"); | |
| return false; | |
| } | |
| /* We currently handle outer loops like this: | |
| | | |
| ForeFirst <------\ } | |
| Blocks | } ForeBlocks of L | |
| ForeLast | } | |
| | | | |
| ... | | |
| | | | |
| ForeFirst <----\ | } | |
| Blocks | | } ForeBlocks of a inner loop of L | |
| ForeLast | | } | |
| | | | | |
| JamLoopFirst <\ | | } | |
| Blocks | | | } JamLoopBlocks of the innermost loop | |
| JamLoopLast -/ | | } | |
| | | | | |
| AftFirst | | } | |
| Blocks | | } AftBlocks of a inner loop of L | |
| AftLast ------/ | } | |
| | | | |
| ... | | |
| | | | |
| AftFirst | } | |
| Blocks | } AftBlocks of L | |
| AftLast --------/ } | |
| | | |
| There are (theoretically) any number of blocks in ForeBlocks, SubLoopBlocks | |
| and AftBlocks, providing that there is one edge from Fores to SubLoops, | |
| one edge from SubLoops to Afts and a single outer loop exit (from Afts). | |
| In practice we currently limit Aft blocks to a single block, and limit | |
| things further in the profitablility checks of the unroll and jam pass. | |
| Because of the way we rearrange basic blocks, we also require that | |
| the Fore blocks of L on all unrolled iterations are safe to move before the | |
| blocks of the direct child of L of all iterations. So we require that the | |
| phi node looping operands of ForeHeader can be moved to at least the end of | |
| ForeEnd, so that we can arrange cloned Fore Blocks before the subloop and | |
| match up Phi's correctly. | |
| i.e. The old order of blocks used to be | |
| (F1)1 (F2)1 J1_1 J1_2 (A2)1 (A1)1 (F1)2 (F2)2 J2_1 J2_2 (A2)2 (A1)2. | |
| It needs to be safe to transform this to | |
| (F1)1 (F1)2 (F2)1 (F2)2 J1_1 J1_2 J2_1 J2_2 (A2)1 (A2)2 (A1)1 (A1)2. | |
| There are then a number of checks along the lines of no calls, no | |
| exceptions, inner loop IV is consistent, etc. Note that for loops requiring | |
| runtime unrolling, UnrollRuntimeLoopRemainder can also fail in | |
| UnrollAndJamLoop if the trip count cannot be easily calculated. | |
| */ | |
| // Split blocks into Fore/SubLoop/Aft based on dominators | |
| Loop *JamLoop = getInnerMostLoop(L); | |
| BasicBlockSet SubLoopBlocks; | |
| DenseMap<Loop *, BasicBlockSet> ForeBlocksMap; | |
| DenseMap<Loop *, BasicBlockSet> AftBlocksMap; | |
| if (!partitionOuterLoopBlocks(*L, *JamLoop, SubLoopBlocks, ForeBlocksMap, | |
| AftBlocksMap, DT)) { | |
| LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; Incompatible loop layout\n"); | |
| return false; | |
| } | |
| // Aft blocks may need to move instructions to fore blocks, which becomes more | |
| // difficult if there are multiple (potentially conditionally executed) | |
| // blocks. For now we just exclude loops with multiple aft blocks. | |
| if (AftBlocksMap[L].size() != 1) { | |
| LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; Can't currently handle " | |
| "multiple blocks after the loop\n"); | |
| return false; | |
| } | |
| // Check inner loop backedge count is consistent on all iterations of the | |
| // outer loop | |
| if (any_of(L->getLoopsInPreorder(), [&SE](Loop *SubLoop) { | |
| return !hasIterationCountInvariantInParent(SubLoop, SE); | |
| })) { | |
| LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; Inner loop iteration count is " | |
| "not consistent on each iteration\n"); | |
| return false; | |
| } | |
| // Check the loop safety info for exceptions. | |
| SimpleLoopSafetyInfo LSI; | |
| LSI.computeLoopSafetyInfo(L); | |
| if (LSI.anyBlockMayThrow()) { | |
| LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; Something may throw\n"); | |
| return false; | |
| } | |
| // We've ruled out the easy stuff and now need to check that there are no | |
| // interdependencies which may prevent us from moving the: | |
| // ForeBlocks before Subloop and AftBlocks. | |
| // Subloop before AftBlocks. | |
| // ForeBlock phi operands before the subloop | |
| // Make sure we can move all instructions we need to before the subloop | |
| BasicBlock *Header = L->getHeader(); | |
| BasicBlock *Latch = L->getLoopLatch(); | |
| BasicBlockSet AftBlocks = AftBlocksMap[L]; | |
| Loop *SubLoop = L->getSubLoops()[0]; | |
| if (!processHeaderPhiOperands( | |
| Header, Latch, AftBlocks, [&AftBlocks, &SubLoop](Instruction *I) { | |
| if (SubLoop->contains(I->getParent())) | |
| return false; | |
| if (AftBlocks.count(I->getParent())) { | |
| // If we hit a phi node in afts we know we are done (probably | |
| // LCSSA) | |
| if (isa<PHINode>(I)) | |
| return false; | |
| // Can't move instructions with side effects or memory | |
| // reads/writes | |
| if (I->mayHaveSideEffects() || I->mayReadOrWriteMemory()) | |
| return false; | |
| } | |
| // Keep going | |
| return true; | |
| })) { | |
| LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; can't move required " | |
| "instructions after subloop to before it\n"); | |
| return false; | |
| } | |
| // Check for memory dependencies which prohibit the unrolling we are doing. | |
| // Because of the way we are unrolling Fore/Sub/Aft blocks, we need to check | |
| // there are no dependencies between Fore-Sub, Fore-Aft, Sub-Aft and Sub-Sub. | |
| if (!checkDependencies(*L, SubLoopBlocks, ForeBlocksMap, AftBlocksMap, DI, | |
| LI)) { | |
| LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; failed dependency check\n"); | |
| return false; | |
| } | |
| return true; | |
| } |