| //===-- LICM.cpp - Loop Invariant Code Motion Pass ------------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass performs loop invariant code motion, attempting to remove as much |
| // code from the body of a loop as possible. It does this by either hoisting |
| // code into the preheader block, or by sinking code to the exit blocks if it is |
| // safe. This pass also promotes must-aliased memory locations in the loop to |
| // live in registers, thus hoisting and sinking "invariant" loads and stores. |
| // |
| // This pass uses alias analysis for two purposes: |
| // |
| // 1. Moving loop invariant loads and calls out of loops. If we can determine |
| // that a load or call inside of a loop never aliases anything stored to, |
| // we can hoist it or sink it like any other instruction. |
| // 2. Scalar Promotion of Memory - If there is a store instruction inside of |
| // the loop, we try to move the store to happen AFTER the loop instead of |
| // inside of the loop. This can only happen if a few conditions are true: |
| // A. The pointer stored through is loop invariant |
| // B. There are no stores or loads in the loop which _may_ alias the |
| // pointer. There are no calls in the loop which mod/ref the pointer. |
| // If these conditions are true, we can promote the loads and stores in the |
| // loop of the pointer to use a temporary alloca'd variable. We then use |
| // the SSAUpdater to construct the appropriate SSA form for the value. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar/LICM.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/AliasAnalysis.h" |
| #include "llvm/Analysis/AliasSetTracker.h" |
| #include "llvm/Analysis/BasicAliasAnalysis.h" |
| #include "llvm/Analysis/CaptureTracking.h" |
| #include "llvm/Analysis/ConstantFolding.h" |
| #include "llvm/Analysis/GlobalsModRef.h" |
| #include "llvm/Analysis/Loads.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/LoopPass.h" |
| #include "llvm/Analysis/MemoryBuiltins.h" |
| #include "llvm/Analysis/MemorySSA.h" |
| #include "llvm/Analysis/OptimizationRemarkEmitter.h" |
| #include "llvm/Analysis/ScalarEvolution.h" |
| #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h" |
| #include "llvm/Analysis/TargetLibraryInfo.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/IR/CFG.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DataLayout.h" |
| #include "llvm/IR/DerivedTypes.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/IR/LLVMContext.h" |
| #include "llvm/IR/Metadata.h" |
| #include "llvm/IR/PredIteratorCache.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Transforms/Scalar/LoopPassManager.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Transforms/Utils/LoopUtils.h" |
| #include "llvm/Transforms/Utils/SSAUpdater.h" |
| #include <algorithm> |
| #include <utility> |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "licm" |
| |
| STATISTIC(NumSunk, "Number of instructions sunk out of loop"); |
| STATISTIC(NumHoisted, "Number of instructions hoisted out of loop"); |
| STATISTIC(NumMovedLoads, "Number of load insts hoisted or sunk"); |
| STATISTIC(NumMovedCalls, "Number of call insts hoisted or sunk"); |
| STATISTIC(NumPromoted, "Number of memory locations promoted to registers"); |
| |
| /// Memory promotion is enabled by default. |
| static cl::opt<bool> |
| DisablePromotion("disable-licm-promotion", cl::Hidden, cl::init(false), |
| cl::desc("Disable memory promotion in LICM pass")); |
| |
| static cl::opt<uint32_t> MaxNumUsesTraversed( |
| "licm-max-num-uses-traversed", cl::Hidden, cl::init(8), |
| cl::desc("Max num uses visited for identifying load " |
| "invariance in loop using invariant start (default = 8)")); |
| |
| static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI); |
| static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop, |
| const LoopSafetyInfo *SafetyInfo, |
| TargetTransformInfo *TTI, bool &FreeInLoop); |
| static bool hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop, |
| const LoopSafetyInfo *SafetyInfo, |
| OptimizationRemarkEmitter *ORE); |
| static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT, |
| const Loop *CurLoop, LoopSafetyInfo *SafetyInfo, |
| OptimizationRemarkEmitter *ORE, bool FreeInLoop); |
| static bool isSafeToExecuteUnconditionally(Instruction &Inst, |
| const DominatorTree *DT, |
| const Loop *CurLoop, |
| const LoopSafetyInfo *SafetyInfo, |
| OptimizationRemarkEmitter *ORE, |
| const Instruction *CtxI = nullptr); |
| static bool pointerInvalidatedByLoop(Value *V, uint64_t Size, |
| const AAMDNodes &AAInfo, |
| AliasSetTracker *CurAST); |
| static Instruction * |
| CloneInstructionInExitBlock(Instruction &I, BasicBlock &ExitBlock, PHINode &PN, |
| const LoopInfo *LI, |
| const LoopSafetyInfo *SafetyInfo); |
| |
| namespace { |
| struct LoopInvariantCodeMotion { |
| bool runOnLoop(Loop *L, AliasAnalysis *AA, LoopInfo *LI, DominatorTree *DT, |
| TargetLibraryInfo *TLI, TargetTransformInfo *TTI, |
| ScalarEvolution *SE, MemorySSA *MSSA, |
| OptimizationRemarkEmitter *ORE, bool DeleteAST); |
| |
| DenseMap<Loop *, AliasSetTracker *> &getLoopToAliasSetMap() { |
| return LoopToAliasSetMap; |
| } |
| |
| private: |
| DenseMap<Loop *, AliasSetTracker *> LoopToAliasSetMap; |
| |
| AliasSetTracker *collectAliasInfoForLoop(Loop *L, LoopInfo *LI, |
| AliasAnalysis *AA); |
| }; |
| |
| struct LegacyLICMPass : public LoopPass { |
| static char ID; // Pass identification, replacement for typeid |
| LegacyLICMPass() : LoopPass(ID) { |
| initializeLegacyLICMPassPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnLoop(Loop *L, LPPassManager &LPM) override { |
| if (skipLoop(L)) { |
| // If we have run LICM on a previous loop but now we are skipping |
| // (because we've hit the opt-bisect limit), we need to clear the |
| // loop alias information. |
| for (auto <AS : LICM.getLoopToAliasSetMap()) |
| delete LTAS.second; |
| LICM.getLoopToAliasSetMap().clear(); |
| return false; |
| } |
| |
| auto *SE = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>(); |
| MemorySSA *MSSA = EnableMSSALoopDependency |
| ? (&getAnalysis<MemorySSAWrapperPass>().getMSSA()) |
| : nullptr; |
| // For the old PM, we can't use OptimizationRemarkEmitter as an analysis |
| // pass. Function analyses need to be preserved across loop transformations |
| // but ORE cannot be preserved (see comment before the pass definition). |
| OptimizationRemarkEmitter ORE(L->getHeader()->getParent()); |
| return LICM.runOnLoop(L, |
| &getAnalysis<AAResultsWrapperPass>().getAAResults(), |
| &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(), |
| &getAnalysis<DominatorTreeWrapperPass>().getDomTree(), |
| &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(), |
| &getAnalysis<TargetTransformInfoWrapperPass>().getTTI( |
| *L->getHeader()->getParent()), |
| SE ? &SE->getSE() : nullptr, MSSA, &ORE, false); |
| } |
| |
| /// This transformation requires natural loop information & requires that |
| /// loop preheaders be inserted into the CFG... |
| /// |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.addPreserved<DominatorTreeWrapperPass>(); |
| AU.addPreserved<LoopInfoWrapperPass>(); |
| AU.addRequired<TargetLibraryInfoWrapperPass>(); |
| if (EnableMSSALoopDependency) |
| AU.addRequired<MemorySSAWrapperPass>(); |
| AU.addRequired<TargetTransformInfoWrapperPass>(); |
| getLoopAnalysisUsage(AU); |
| } |
| |
| using llvm::Pass::doFinalization; |
| |
| bool doFinalization() override { |
| assert(LICM.getLoopToAliasSetMap().empty() && |
| "Didn't free loop alias sets"); |
| return false; |
| } |
| |
| private: |
| LoopInvariantCodeMotion LICM; |
| |
| /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info. |
| void cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, |
| Loop *L) override; |
| |
| /// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias |
| /// set. |
| void deleteAnalysisValue(Value *V, Loop *L) override; |
| |
| /// Simple Analysis hook. Delete loop L from alias set map. |
| void deleteAnalysisLoop(Loop *L) override; |
| }; |
| } // namespace |
| |
| PreservedAnalyses LICMPass::run(Loop &L, LoopAnalysisManager &AM, |
| LoopStandardAnalysisResults &AR, LPMUpdater &) { |
| const auto &FAM = |
| AM.getResult<FunctionAnalysisManagerLoopProxy>(L, AR).getManager(); |
| Function *F = L.getHeader()->getParent(); |
| |
| auto *ORE = FAM.getCachedResult<OptimizationRemarkEmitterAnalysis>(*F); |
| // FIXME: This should probably be optional rather than required. |
| if (!ORE) |
| report_fatal_error("LICM: OptimizationRemarkEmitterAnalysis not " |
| "cached at a higher level"); |
| |
| LoopInvariantCodeMotion LICM; |
| if (!LICM.runOnLoop(&L, &AR.AA, &AR.LI, &AR.DT, &AR.TLI, &AR.TTI, &AR.SE, |
| AR.MSSA, ORE, true)) |
| return PreservedAnalyses::all(); |
| |
| auto PA = getLoopPassPreservedAnalyses(); |
| |
| PA.preserve<DominatorTreeAnalysis>(); |
| PA.preserve<LoopAnalysis>(); |
| |
| return PA; |
| } |
| |
| char LegacyLICMPass::ID = 0; |
| INITIALIZE_PASS_BEGIN(LegacyLICMPass, "licm", "Loop Invariant Code Motion", |
| false, false) |
| INITIALIZE_PASS_DEPENDENCY(LoopPass) |
| INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass) |
| INITIALIZE_PASS_END(LegacyLICMPass, "licm", "Loop Invariant Code Motion", false, |
| false) |
| |
| Pass *llvm::createLICMPass() { return new LegacyLICMPass(); } |
| |
| /// Hoist expressions out of the specified loop. Note, alias info for inner |
| /// loop is not preserved so it is not a good idea to run LICM multiple |
| /// times on one loop. |
| /// We should delete AST for inner loops in the new pass manager to avoid |
| /// memory leak. |
| /// |
| bool LoopInvariantCodeMotion::runOnLoop( |
| Loop *L, AliasAnalysis *AA, LoopInfo *LI, DominatorTree *DT, |
| TargetLibraryInfo *TLI, TargetTransformInfo *TTI, ScalarEvolution *SE, |
| MemorySSA *MSSA, OptimizationRemarkEmitter *ORE, bool DeleteAST) { |
| bool Changed = false; |
| |
| assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form."); |
| |
| AliasSetTracker *CurAST = collectAliasInfoForLoop(L, LI, AA); |
| |
| // Get the preheader block to move instructions into... |
| BasicBlock *Preheader = L->getLoopPreheader(); |
| |
| // Compute loop safety information. |
| LoopSafetyInfo SafetyInfo; |
| computeLoopSafetyInfo(&SafetyInfo, L); |
| |
| // We want to visit all of the instructions in this loop... that are not parts |
| // of our subloops (they have already had their invariants hoisted out of |
| // their loop, into this loop, so there is no need to process the BODIES of |
| // the subloops). |
| // |
| // Traverse the body of the loop in depth first order on the dominator tree so |
| // that we are guaranteed to see definitions before we see uses. This allows |
| // us to sink instructions in one pass, without iteration. After sinking |
| // instructions, we perform another pass to hoist them out of the loop. |
| // |
| if (L->hasDedicatedExits()) |
| Changed |= sinkRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, TTI, L, |
| CurAST, &SafetyInfo, ORE); |
| if (Preheader) |
| Changed |= hoistRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, L, |
| CurAST, &SafetyInfo, ORE); |
| |
| // Now that all loop invariants have been removed from the loop, promote any |
| // memory references to scalars that we can. |
| // Don't sink stores from loops without dedicated block exits. Exits |
| // containing indirect branches are not transformed by loop simplify, |
| // make sure we catch that. An additional load may be generated in the |
| // preheader for SSA updater, so also avoid sinking when no preheader |
| // is available. |
| if (!DisablePromotion && Preheader && L->hasDedicatedExits()) { |
| // Figure out the loop exits and their insertion points |
| SmallVector<BasicBlock *, 8> ExitBlocks; |
| L->getUniqueExitBlocks(ExitBlocks); |
| |
| // We can't insert into a catchswitch. |
| bool HasCatchSwitch = llvm::any_of(ExitBlocks, [](BasicBlock *Exit) { |
| return isa<CatchSwitchInst>(Exit->getTerminator()); |
| }); |
| |
| if (!HasCatchSwitch) { |
| SmallVector<Instruction *, 8> InsertPts; |
| InsertPts.reserve(ExitBlocks.size()); |
| for (BasicBlock *ExitBlock : ExitBlocks) |
| InsertPts.push_back(&*ExitBlock->getFirstInsertionPt()); |
| |
| PredIteratorCache PIC; |
| |
| bool Promoted = false; |
| |
| // Loop over all of the alias sets in the tracker object. |
| for (AliasSet &AS : *CurAST) { |
| // We can promote this alias set if it has a store, if it is a "Must" |
| // alias set, if the pointer is loop invariant, and if we are not |
| // eliminating any volatile loads or stores. |
| if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() || |
| AS.isVolatile() || !L->isLoopInvariant(AS.begin()->getValue())) |
| continue; |
| |
| assert( |
| !AS.empty() && |
| "Must alias set should have at least one pointer element in it!"); |
| |
| SmallSetVector<Value *, 8> PointerMustAliases; |
| for (const auto &ASI : AS) |
| PointerMustAliases.insert(ASI.getValue()); |
| |
| Promoted |= promoteLoopAccessesToScalars(PointerMustAliases, ExitBlocks, |
| InsertPts, PIC, LI, DT, TLI, L, |
| CurAST, &SafetyInfo, ORE); |
| } |
| |
| // Once we have promoted values across the loop body we have to |
| // recursively reform LCSSA as any nested loop may now have values defined |
| // within the loop used in the outer loop. |
| // FIXME: This is really heavy handed. It would be a bit better to use an |
| // SSAUpdater strategy during promotion that was LCSSA aware and reformed |
| // it as it went. |
| if (Promoted) |
| formLCSSARecursively(*L, *DT, LI, SE); |
| |
| Changed |= Promoted; |
| } |
| } |
| |
| // Check that neither this loop nor its parent have had LCSSA broken. LICM is |
| // specifically moving instructions across the loop boundary and so it is |
| // especially in need of sanity checking here. |
| assert(L->isLCSSAForm(*DT) && "Loop not left in LCSSA form after LICM!"); |
| assert((!L->getParentLoop() || L->getParentLoop()->isLCSSAForm(*DT)) && |
| "Parent loop not left in LCSSA form after LICM!"); |
| |
| // If this loop is nested inside of another one, save the alias information |
| // for when we process the outer loop. |
| if (L->getParentLoop() && !DeleteAST) |
| LoopToAliasSetMap[L] = CurAST; |
| else |
| delete CurAST; |
| |
| if (Changed && SE) |
| SE->forgetLoopDispositions(L); |
| return Changed; |
| } |
| |
| /// Walk the specified region of the CFG (defined by all blocks dominated by |
| /// the specified block, and that are in the current loop) in reverse depth |
| /// first order w.r.t the DominatorTree. This allows us to visit uses before |
| /// definitions, allowing us to sink a loop body in one pass without iteration. |
| /// |
| bool llvm::sinkRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI, |
| DominatorTree *DT, TargetLibraryInfo *TLI, |
| TargetTransformInfo *TTI, Loop *CurLoop, |
| AliasSetTracker *CurAST, LoopSafetyInfo *SafetyInfo, |
| OptimizationRemarkEmitter *ORE) { |
| |
| // Verify inputs. |
| assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr && |
| CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr && |
| "Unexpected input to sinkRegion"); |
| |
| // We want to visit children before parents. We will enque all the parents |
| // before their children in the worklist and process the worklist in reverse |
| // order. |
| SmallVector<DomTreeNode *, 16> Worklist = collectChildrenInLoop(N, CurLoop); |
| |
| bool Changed = false; |
| for (DomTreeNode *DTN : reverse(Worklist)) { |
| BasicBlock *BB = DTN->getBlock(); |
| // Only need to process the contents of this block if it is not part of a |
| // subloop (which would already have been processed). |
| if (inSubLoop(BB, CurLoop, LI)) |
| continue; |
| |
| for (BasicBlock::iterator II = BB->end(); II != BB->begin();) { |
| Instruction &I = *--II; |
| |
| // If the instruction is dead, we would try to sink it because it isn't |
| // used in the loop, instead, just delete it. |
| if (isInstructionTriviallyDead(&I, TLI)) { |
| LLVM_DEBUG(dbgs() << "LICM deleting dead inst: " << I << '\n'); |
| salvageDebugInfo(I); |
| ++II; |
| CurAST->deleteValue(&I); |
| I.eraseFromParent(); |
| Changed = true; |
| continue; |
| } |
| |
| // Check to see if we can sink this instruction to the exit blocks |
| // of the loop. We can do this if the all users of the instruction are |
| // outside of the loop. In this case, it doesn't even matter if the |
| // operands of the instruction are loop invariant. |
| // |
| bool FreeInLoop = false; |
| if (isNotUsedOrFreeInLoop(I, CurLoop, SafetyInfo, TTI, FreeInLoop) && |
| canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, SafetyInfo, ORE)) { |
| if (sink(I, LI, DT, CurLoop, SafetyInfo, ORE, FreeInLoop)) { |
| if (!FreeInLoop) { |
| ++II; |
| CurAST->deleteValue(&I); |
| I.eraseFromParent(); |
| } |
| Changed = true; |
| } |
| } |
| } |
| } |
| return Changed; |
| } |
| |
| /// Walk the specified region of the CFG (defined by all blocks dominated by |
| /// the specified block, and that are in the current loop) in depth first |
| /// order w.r.t the DominatorTree. This allows us to visit definitions before |
| /// uses, allowing us to hoist a loop body in one pass without iteration. |
| /// |
| bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI, |
| DominatorTree *DT, TargetLibraryInfo *TLI, Loop *CurLoop, |
| AliasSetTracker *CurAST, LoopSafetyInfo *SafetyInfo, |
| OptimizationRemarkEmitter *ORE) { |
| // Verify inputs. |
| assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr && |
| CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr && |
| "Unexpected input to hoistRegion"); |
| |
| // We want to visit parents before children. We will enque all the parents |
| // before their children in the worklist and process the worklist in order. |
| SmallVector<DomTreeNode *, 16> Worklist = collectChildrenInLoop(N, CurLoop); |
| |
| bool Changed = false; |
| for (DomTreeNode *DTN : Worklist) { |
| BasicBlock *BB = DTN->getBlock(); |
| // Only need to process the contents of this block if it is not part of a |
| // subloop (which would already have been processed). |
| if (inSubLoop(BB, CurLoop, LI)) |
| continue; |
| |
| // Keep track of whether the prefix of instructions visited so far are such |
| // that the next instruction visited is guaranteed to execute if the loop |
| // is entered. |
| bool IsMustExecute = CurLoop->getHeader() == BB; |
| |
| for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) { |
| Instruction &I = *II++; |
| // Try constant folding this instruction. If all the operands are |
| // constants, it is technically hoistable, but it would be better to |
| // just fold it. |
| if (Constant *C = ConstantFoldInstruction( |
| &I, I.getModule()->getDataLayout(), TLI)) { |
| LLVM_DEBUG(dbgs() << "LICM folding inst: " << I << " --> " << *C |
| << '\n'); |
| CurAST->copyValue(&I, C); |
| I.replaceAllUsesWith(C); |
| if (isInstructionTriviallyDead(&I, TLI)) { |
| CurAST->deleteValue(&I); |
| I.eraseFromParent(); |
| } |
| Changed = true; |
| continue; |
| } |
| |
| // Try hoisting the instruction out to the preheader. We can only do |
| // this if all of the operands of the instruction are loop invariant and |
| // if it is safe to hoist the instruction. |
| // |
| if (CurLoop->hasLoopInvariantOperands(&I) && |
| canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, SafetyInfo, ORE) && |
| (IsMustExecute || |
| isSafeToExecuteUnconditionally( |
| I, DT, CurLoop, SafetyInfo, ORE, |
| CurLoop->getLoopPreheader()->getTerminator()))) { |
| Changed |= hoist(I, DT, CurLoop, SafetyInfo, ORE); |
| continue; |
| } |
| |
| // Attempt to remove floating point division out of the loop by |
| // converting it to a reciprocal multiplication. |
| if (I.getOpcode() == Instruction::FDiv && |
| CurLoop->isLoopInvariant(I.getOperand(1)) && |
| I.hasAllowReciprocal()) { |
| auto Divisor = I.getOperand(1); |
| auto One = llvm::ConstantFP::get(Divisor->getType(), 1.0); |
| auto ReciprocalDivisor = BinaryOperator::CreateFDiv(One, Divisor); |
| ReciprocalDivisor->setFastMathFlags(I.getFastMathFlags()); |
| ReciprocalDivisor->insertBefore(&I); |
| |
| auto Product = |
| BinaryOperator::CreateFMul(I.getOperand(0), ReciprocalDivisor); |
| Product->setFastMathFlags(I.getFastMathFlags()); |
| Product->insertAfter(&I); |
| I.replaceAllUsesWith(Product); |
| I.eraseFromParent(); |
| |
| hoist(*ReciprocalDivisor, DT, CurLoop, SafetyInfo, ORE); |
| Changed = true; |
| continue; |
| } |
| |
| if (IsMustExecute) |
| IsMustExecute = isGuaranteedToTransferExecutionToSuccessor(&I); |
| } |
| } |
| |
| return Changed; |
| } |
| |
| // Return true if LI is invariant within scope of the loop. LI is invariant if |
| // CurLoop is dominated by an invariant.start representing the same memory |
| // location and size as the memory location LI loads from, and also the |
| // invariant.start has no uses. |
| static bool isLoadInvariantInLoop(LoadInst *LI, DominatorTree *DT, |
| Loop *CurLoop) { |
| Value *Addr = LI->getOperand(0); |
| const DataLayout &DL = LI->getModule()->getDataLayout(); |
| const uint32_t LocSizeInBits = DL.getTypeSizeInBits( |
| cast<PointerType>(Addr->getType())->getElementType()); |
| |
| // if the type is i8 addrspace(x)*, we know this is the type of |
| // llvm.invariant.start operand |
| auto *PtrInt8Ty = PointerType::get(Type::getInt8Ty(LI->getContext()), |
| LI->getPointerAddressSpace()); |
| unsigned BitcastsVisited = 0; |
| // Look through bitcasts until we reach the i8* type (this is invariant.start |
| // operand type). |
| while (Addr->getType() != PtrInt8Ty) { |
| auto *BC = dyn_cast<BitCastInst>(Addr); |
| // Avoid traversing high number of bitcast uses. |
| if (++BitcastsVisited > MaxNumUsesTraversed || !BC) |
| return false; |
| Addr = BC->getOperand(0); |
| } |
| |
| unsigned UsesVisited = 0; |
| // Traverse all uses of the load operand value, to see if invariant.start is |
| // one of the uses, and whether it dominates the load instruction. |
| for (auto *U : Addr->users()) { |
| // Avoid traversing for Load operand with high number of users. |
| if (++UsesVisited > MaxNumUsesTraversed) |
| return false; |
| IntrinsicInst *II = dyn_cast<IntrinsicInst>(U); |
| // If there are escaping uses of invariant.start instruction, the load maybe |
| // non-invariant. |
| if (!II || II->getIntrinsicID() != Intrinsic::invariant_start || |
| !II->use_empty()) |
| continue; |
| unsigned InvariantSizeInBits = |
| cast<ConstantInt>(II->getArgOperand(0))->getSExtValue() * 8; |
| // Confirm the invariant.start location size contains the load operand size |
| // in bits. Also, the invariant.start should dominate the load, and we |
| // should not hoist the load out of a loop that contains this dominating |
| // invariant.start. |
| if (LocSizeInBits <= InvariantSizeInBits && |
| DT->properlyDominates(II->getParent(), CurLoop->getHeader())) |
| return true; |
| } |
| |
| return false; |
| } |
| |
| bool llvm::canSinkOrHoistInst(Instruction &I, AAResults *AA, DominatorTree *DT, |
| Loop *CurLoop, AliasSetTracker *CurAST, |
| LoopSafetyInfo *SafetyInfo, |
| OptimizationRemarkEmitter *ORE) { |
| // SafetyInfo is nullptr if we are checking for sinking from preheader to |
| // loop body. |
| const bool SinkingToLoopBody = !SafetyInfo; |
| // Loads have extra constraints we have to verify before we can hoist them. |
| if (LoadInst *LI = dyn_cast<LoadInst>(&I)) { |
| if (!LI->isUnordered()) |
| return false; // Don't sink/hoist volatile or ordered atomic loads! |
| |
| // Loads from constant memory are always safe to move, even if they end up |
| // in the same alias set as something that ends up being modified. |
| if (AA->pointsToConstantMemory(LI->getOperand(0))) |
| return true; |
| if (LI->getMetadata(LLVMContext::MD_invariant_load)) |
| return true; |
| |
| if (LI->isAtomic() && SinkingToLoopBody) |
| return false; // Don't sink unordered atomic loads to loop body. |
| |
| // This checks for an invariant.start dominating the load. |
| if (isLoadInvariantInLoop(LI, DT, CurLoop)) |
| return true; |
| |
| // Don't hoist loads which have may-aliased stores in loop. |
| uint64_t Size = 0; |
| if (LI->getType()->isSized()) |
| Size = I.getModule()->getDataLayout().getTypeStoreSize(LI->getType()); |
| |
| AAMDNodes AAInfo; |
| LI->getAAMetadata(AAInfo); |
| |
| bool Invalidated = |
| pointerInvalidatedByLoop(LI->getOperand(0), Size, AAInfo, CurAST); |
| // Check loop-invariant address because this may also be a sinkable load |
| // whose address is not necessarily loop-invariant. |
| if (ORE && Invalidated && CurLoop->isLoopInvariant(LI->getPointerOperand())) |
| ORE->emit([&]() { |
| return OptimizationRemarkMissed( |
| DEBUG_TYPE, "LoadWithLoopInvariantAddressInvalidated", LI) |
| << "failed to move load with loop-invariant address " |
| "because the loop may invalidate its value"; |
| }); |
| |
| return !Invalidated; |
| } else if (CallInst *CI = dyn_cast<CallInst>(&I)) { |
| // Don't sink or hoist dbg info; it's legal, but not useful. |
| if (isa<DbgInfoIntrinsic>(I)) |
| return false; |
| |
| // Don't sink calls which can throw. |
| if (CI->mayThrow()) |
| return false; |
| |
| // Handle simple cases by querying alias analysis. |
| FunctionModRefBehavior Behavior = AA->getModRefBehavior(CI); |
| if (Behavior == FMRB_DoesNotAccessMemory) |
| return true; |
| if (AliasAnalysis::onlyReadsMemory(Behavior)) { |
| // A readonly argmemonly function only reads from memory pointed to by |
| // it's arguments with arbitrary offsets. If we can prove there are no |
| // writes to this memory in the loop, we can hoist or sink. |
| if (AliasAnalysis::onlyAccessesArgPointees(Behavior)) { |
| for (Value *Op : CI->arg_operands()) |
| if (Op->getType()->isPointerTy() && |
| pointerInvalidatedByLoop(Op, MemoryLocation::UnknownSize, |
| AAMDNodes(), CurAST)) |
| return false; |
| return true; |
| } |
| // If this call only reads from memory and there are no writes to memory |
| // in the loop, we can hoist or sink the call as appropriate. |
| bool FoundMod = false; |
| for (AliasSet &AS : *CurAST) { |
| if (!AS.isForwardingAliasSet() && AS.isMod()) { |
| FoundMod = true; |
| break; |
| } |
| } |
| if (!FoundMod) |
| return true; |
| } |
| |
| // FIXME: This should use mod/ref information to see if we can hoist or |
| // sink the call. |
| |
| return false; |
| } |
| |
| // Only these instructions are hoistable/sinkable. |
| if (!isa<BinaryOperator>(I) && !isa<CastInst>(I) && !isa<SelectInst>(I) && |
| !isa<GetElementPtrInst>(I) && !isa<CmpInst>(I) && |
| !isa<InsertElementInst>(I) && !isa<ExtractElementInst>(I) && |
| !isa<ShuffleVectorInst>(I) && !isa<ExtractValueInst>(I) && |
| !isa<InsertValueInst>(I)) |
| return false; |
| |
| // If we are checking for sinking from preheader to loop body it will be |
| // always safe as there is no speculative execution. |
| if (SinkingToLoopBody) |
| return true; |
| |
| // TODO: Plumb the context instruction through to make hoisting and sinking |
| // more powerful. Hoisting of loads already works due to the special casing |
| // above. |
| return isSafeToExecuteUnconditionally(I, DT, CurLoop, SafetyInfo, nullptr); |
| } |
| |
| /// Returns true if a PHINode is a trivially replaceable with an |
| /// Instruction. |
| /// This is true when all incoming values are that instruction. |
| /// This pattern occurs most often with LCSSA PHI nodes. |
| /// |
| static bool isTriviallyReplaceablePHI(const PHINode &PN, const Instruction &I) { |
| for (const Value *IncValue : PN.incoming_values()) |
| if (IncValue != &I) |
| return false; |
| |
| return true; |
| } |
| |
| /// Return true if the instruction is free in the loop. |
| static bool isFreeInLoop(const Instruction &I, const Loop *CurLoop, |
| const TargetTransformInfo *TTI) { |
| |
| if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(&I)) { |
| if (TTI->getUserCost(GEP) != TargetTransformInfo::TCC_Free) |
| return false; |
| // For a GEP, we cannot simply use getUserCost because currently it |
| // optimistically assume that a GEP will fold into addressing mode |
| // regardless of its users. |
| const BasicBlock *BB = GEP->getParent(); |
| for (const User *U : GEP->users()) { |
| const Instruction *UI = cast<Instruction>(U); |
| if (CurLoop->contains(UI) && |
| (BB != UI->getParent() || |
| (!isa<StoreInst>(UI) && !isa<LoadInst>(UI)))) |
| return false; |
| } |
| return true; |
| } else |
| return TTI->getUserCost(&I) == TargetTransformInfo::TCC_Free; |
| } |
| |
| /// Return true if the only users of this instruction are outside of |
| /// the loop. If this is true, we can sink the instruction to the exit |
| /// blocks of the loop. |
| /// |
| /// We also return true if the instruction could be folded away in lowering. |
| /// (e.g., a GEP can be folded into a load as an addressing mode in the loop). |
| static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop, |
| const LoopSafetyInfo *SafetyInfo, |
| TargetTransformInfo *TTI, bool &FreeInLoop) { |
| const auto &BlockColors = SafetyInfo->BlockColors; |
| bool IsFree = isFreeInLoop(I, CurLoop, TTI); |
| for (const User *U : I.users()) { |
| const Instruction *UI = cast<Instruction>(U); |
| if (const PHINode *PN = dyn_cast<PHINode>(UI)) { |
| const BasicBlock *BB = PN->getParent(); |
| // We cannot sink uses in catchswitches. |
| if (isa<CatchSwitchInst>(BB->getTerminator())) |
| return false; |
| |
| // We need to sink a callsite to a unique funclet. Avoid sinking if the |
| // phi use is too muddled. |
| if (isa<CallInst>(I)) |
| if (!BlockColors.empty() && |
| BlockColors.find(const_cast<BasicBlock *>(BB))->second.size() != 1) |
| return false; |
| } |
| |
| if (CurLoop->contains(UI)) { |
| if (IsFree) { |
| FreeInLoop = true; |
| continue; |
| } |
| return false; |
| } |
| } |
| return true; |
| } |
| |
| static Instruction * |
| CloneInstructionInExitBlock(Instruction &I, BasicBlock &ExitBlock, PHINode &PN, |
| const LoopInfo *LI, |
| const LoopSafetyInfo *SafetyInfo) { |
| Instruction *New; |
| if (auto *CI = dyn_cast<CallInst>(&I)) { |
| const auto &BlockColors = SafetyInfo->BlockColors; |
| |
| // Sinking call-sites need to be handled differently from other |
| // instructions. The cloned call-site needs a funclet bundle operand |
| // appropriate for it's location in the CFG. |
| SmallVector<OperandBundleDef, 1> OpBundles; |
| for (unsigned BundleIdx = 0, BundleEnd = CI->getNumOperandBundles(); |
| BundleIdx != BundleEnd; ++BundleIdx) { |
| OperandBundleUse Bundle = CI->getOperandBundleAt(BundleIdx); |
| if (Bundle.getTagID() == LLVMContext::OB_funclet) |
| continue; |
| |
| OpBundles.emplace_back(Bundle); |
| } |
| |
| if (!BlockColors.empty()) { |
| const ColorVector &CV = BlockColors.find(&ExitBlock)->second; |
| assert(CV.size() == 1 && "non-unique color for exit block!"); |
| BasicBlock *BBColor = CV.front(); |
| Instruction *EHPad = BBColor->getFirstNonPHI(); |
| if (EHPad->isEHPad()) |
| OpBundles.emplace_back("funclet", EHPad); |
| } |
| |
| New = CallInst::Create(CI, OpBundles); |
| } else { |
| New = I.clone(); |
| } |
| |
| ExitBlock.getInstList().insert(ExitBlock.getFirstInsertionPt(), New); |
| if (!I.getName().empty()) |
| New->setName(I.getName() + ".le"); |
| |
| // Build LCSSA PHI nodes for any in-loop operands. Note that this is |
| // particularly cheap because we can rip off the PHI node that we're |
| // replacing for the number and blocks of the predecessors. |
| // OPT: If this shows up in a profile, we can instead finish sinking all |
| // invariant instructions, and then walk their operands to re-establish |
| // LCSSA. That will eliminate creating PHI nodes just to nuke them when |
| // sinking bottom-up. |
| for (User::op_iterator OI = New->op_begin(), OE = New->op_end(); OI != OE; |
| ++OI) |
| if (Instruction *OInst = dyn_cast<Instruction>(*OI)) |
| if (Loop *OLoop = LI->getLoopFor(OInst->getParent())) |
| if (!OLoop->contains(&PN)) { |
| PHINode *OpPN = |
| PHINode::Create(OInst->getType(), PN.getNumIncomingValues(), |
| OInst->getName() + ".lcssa", &ExitBlock.front()); |
| for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) |
| OpPN->addIncoming(OInst, PN.getIncomingBlock(i)); |
| *OI = OpPN; |
| } |
| return New; |
| } |
| |
| static Instruction *sinkThroughTriviallyReplaceablePHI( |
| PHINode *TPN, Instruction *I, LoopInfo *LI, |
| SmallDenseMap<BasicBlock *, Instruction *, 32> &SunkCopies, |
| const LoopSafetyInfo *SafetyInfo, const Loop *CurLoop) { |
| assert(isTriviallyReplaceablePHI(*TPN, *I) && |
| "Expect only trivially replaceable PHI"); |
| BasicBlock *ExitBlock = TPN->getParent(); |
| Instruction *New; |
| auto It = SunkCopies.find(ExitBlock); |
| if (It != SunkCopies.end()) |
| New = It->second; |
| else |
| New = SunkCopies[ExitBlock] = |
| CloneInstructionInExitBlock(*I, *ExitBlock, *TPN, LI, SafetyInfo); |
| return New; |
| } |
| |
| static bool canSplitPredecessors(PHINode *PN, LoopSafetyInfo *SafetyInfo) { |
| BasicBlock *BB = PN->getParent(); |
| if (!BB->canSplitPredecessors()) |
| return false; |
| // It's not impossible to split EHPad blocks, but if BlockColors already exist |
| // it require updating BlockColors for all offspring blocks accordingly. By |
| // skipping such corner case, we can make updating BlockColors after splitting |
| // predecessor fairly simple. |
| if (!SafetyInfo->BlockColors.empty() && BB->getFirstNonPHI()->isEHPad()) |
| return false; |
| for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { |
| BasicBlock *BBPred = *PI; |
| if (isa<IndirectBrInst>(BBPred->getTerminator())) |
| return false; |
| } |
| return true; |
| } |
| |
| static void splitPredecessorsOfLoopExit(PHINode *PN, DominatorTree *DT, |
| LoopInfo *LI, const Loop *CurLoop, |
| LoopSafetyInfo *SafetyInfo) { |
| #ifndef NDEBUG |
| SmallVector<BasicBlock *, 32> ExitBlocks; |
| CurLoop->getUniqueExitBlocks(ExitBlocks); |
| SmallPtrSet<BasicBlock *, 32> ExitBlockSet(ExitBlocks.begin(), |
| ExitBlocks.end()); |
| #endif |
| BasicBlock *ExitBB = PN->getParent(); |
| assert(ExitBlockSet.count(ExitBB) && "Expect the PHI is in an exit block."); |
| |
| // Split predecessors of the loop exit to make instructions in the loop are |
| // exposed to exit blocks through trivially replaceable PHIs while keeping the |
| // loop in the canonical form where each predecessor of each exit block should |
| // be contained within the loop. For example, this will convert the loop below |
| // from |
| // |
| // LB1: |
| // %v1 = |
| // br %LE, %LB2 |
| // LB2: |
| // %v2 = |
| // br %LE, %LB1 |
| // LE: |
| // %p = phi [%v1, %LB1], [%v2, %LB2] <-- non-trivially replaceable |
| // |
| // to |
| // |
| // LB1: |
| // %v1 = |
| // br %LE.split, %LB2 |
| // LB2: |
| // %v2 = |
| // br %LE.split2, %LB1 |
| // LE.split: |
| // %p1 = phi [%v1, %LB1] <-- trivially replaceable |
| // br %LE |
| // LE.split2: |
| // %p2 = phi [%v2, %LB2] <-- trivially replaceable |
| // br %LE |
| // LE: |
| // %p = phi [%p1, %LE.split], [%p2, %LE.split2] |
| // |
| auto &BlockColors = SafetyInfo->BlockColors; |
| SmallSetVector<BasicBlock *, 8> PredBBs(pred_begin(ExitBB), pred_end(ExitBB)); |
| while (!PredBBs.empty()) { |
| BasicBlock *PredBB = *PredBBs.begin(); |
| assert(CurLoop->contains(PredBB) && |
| "Expect all predecessors are in the loop"); |
| if (PN->getBasicBlockIndex(PredBB) >= 0) { |
| BasicBlock *NewPred = SplitBlockPredecessors( |
| ExitBB, PredBB, ".split.loop.exit", DT, LI, true); |
| // Since we do not allow splitting EH-block with BlockColors in |
| // canSplitPredecessors(), we can simply assign predecessor's color to |
| // the new block. |
| if (!BlockColors.empty()) { |
| // Grab a reference to the ColorVector to be inserted before getting the |
| // reference to the vector we are copying because inserting the new |
| // element in BlockColors might cause the map to be reallocated. |
| ColorVector &ColorsForNewBlock = BlockColors[NewPred]; |
| ColorVector &ColorsForOldBlock = BlockColors[PredBB]; |
| ColorsForNewBlock = ColorsForOldBlock; |
| } |
| } |
| PredBBs.remove(PredBB); |
| } |
| } |
| |
| /// When an instruction is found to only be used outside of the loop, this |
| /// function moves it to the exit blocks and patches up SSA form as needed. |
| /// This method is guaranteed to remove the original instruction from its |
| /// position, and may either delete it or move it to outside of the loop. |
| /// |
| static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT, |
| const Loop *CurLoop, LoopSafetyInfo *SafetyInfo, |
| OptimizationRemarkEmitter *ORE, bool FreeInLoop) { |
| LLVM_DEBUG(dbgs() << "LICM sinking instruction: " << I << "\n"); |
| ORE->emit([&]() { |
| return OptimizationRemark(DEBUG_TYPE, "InstSunk", &I) |
| << "sinking " << ore::NV("Inst", &I); |
| }); |
| bool Changed = false; |
| if (isa<LoadInst>(I)) |
| ++NumMovedLoads; |
| else if (isa<CallInst>(I)) |
| ++NumMovedCalls; |
| ++NumSunk; |
| |
| // Iterate over users to be ready for actual sinking. Replace users via |
| // unrechable blocks with undef and make all user PHIs trivially replcable. |
| SmallPtrSet<Instruction *, 8> VisitedUsers; |
| for (Value::user_iterator UI = I.user_begin(), UE = I.user_end(); UI != UE;) { |
| auto *User = cast<Instruction>(*UI); |
| Use &U = UI.getUse(); |
| ++UI; |
| |
| if (VisitedUsers.count(User) || CurLoop->contains(User)) |
| continue; |
| |
| if (!DT->isReachableFromEntry(User->getParent())) { |
| U = UndefValue::get(I.getType()); |
| Changed = true; |
| continue; |
| } |
| |
| // The user must be a PHI node. |
| PHINode *PN = cast<PHINode>(User); |
| |
| // Surprisingly, instructions can be used outside of loops without any |
| // exits. This can only happen in PHI nodes if the incoming block is |
| // unreachable. |
| BasicBlock *BB = PN->getIncomingBlock(U); |
| if (!DT->isReachableFromEntry(BB)) { |
| U = UndefValue::get(I.getType()); |
| Changed = true; |
| continue; |
| } |
| |
| VisitedUsers.insert(PN); |
| if (isTriviallyReplaceablePHI(*PN, I)) |
| continue; |
| |
| if (!canSplitPredecessors(PN, SafetyInfo)) |
| return Changed; |
| |
| // Split predecessors of the PHI so that we can make users trivially |
| // replaceable. |
| splitPredecessorsOfLoopExit(PN, DT, LI, CurLoop, SafetyInfo); |
| |
| // Should rebuild the iterators, as they may be invalidated by |
| // splitPredecessorsOfLoopExit(). |
| UI = I.user_begin(); |
| UE = I.user_end(); |
| } |
| |
| if (VisitedUsers.empty()) |
| return Changed; |
| |
| #ifndef NDEBUG |
| SmallVector<BasicBlock *, 32> ExitBlocks; |
| CurLoop->getUniqueExitBlocks(ExitBlocks); |
| SmallPtrSet<BasicBlock *, 32> ExitBlockSet(ExitBlocks.begin(), |
| ExitBlocks.end()); |
| #endif |
| |
| // Clones of this instruction. Don't create more than one per exit block! |
| SmallDenseMap<BasicBlock *, Instruction *, 32> SunkCopies; |
| |
| // If this instruction is only used outside of the loop, then all users are |
| // PHI nodes in exit blocks due to LCSSA form. Just RAUW them with clones of |
| // the instruction. |
| SmallSetVector<User*, 8> Users(I.user_begin(), I.user_end()); |
| for (auto *UI : Users) { |
| auto *User = cast<Instruction>(UI); |
| |
| if (CurLoop->contains(User)) |
| continue; |
| |
| PHINode *PN = cast<PHINode>(User); |
| assert(ExitBlockSet.count(PN->getParent()) && |
| "The LCSSA PHI is not in an exit block!"); |
| // The PHI must be trivially replaceable. |
| Instruction *New = sinkThroughTriviallyReplaceablePHI(PN, &I, LI, SunkCopies, |
| SafetyInfo, CurLoop); |
| PN->replaceAllUsesWith(New); |
| PN->eraseFromParent(); |
| Changed = true; |
| } |
| return Changed; |
| } |
| |
| /// When an instruction is found to only use loop invariant operands that |
| /// is safe to hoist, this instruction is called to do the dirty work. |
| /// |
| static bool hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop, |
| const LoopSafetyInfo *SafetyInfo, |
| OptimizationRemarkEmitter *ORE) { |
| auto *Preheader = CurLoop->getLoopPreheader(); |
| LLVM_DEBUG(dbgs() << "LICM hoisting to " << Preheader->getName() << ": " << I |
| << "\n"); |
| ORE->emit([&]() { |
| return OptimizationRemark(DEBUG_TYPE, "Hoisted", &I) << "hoisting " |
| << ore::NV("Inst", &I); |
| }); |
| |
| // Metadata can be dependent on conditions we are hoisting above. |
| // Conservatively strip all metadata on the instruction unless we were |
| // guaranteed to execute I if we entered the loop, in which case the metadata |
| // is valid in the loop preheader. |
| if (I.hasMetadataOtherThanDebugLoc() && |
| // The check on hasMetadataOtherThanDebugLoc is to prevent us from burning |
| // time in isGuaranteedToExecute if we don't actually have anything to |
| // drop. It is a compile time optimization, not required for correctness. |
| !isGuaranteedToExecute(I, DT, CurLoop, SafetyInfo)) |
| I.dropUnknownNonDebugMetadata(); |
| |
| // Move the new node to the Preheader, before its terminator. |
| I.moveBefore(Preheader->getTerminator()); |
| |
| // Do not retain debug locations when we are moving instructions to different |
| // basic blocks, because we want to avoid jumpy line tables. Calls, however, |
| // need to retain their debug locs because they may be inlined. |
| // FIXME: How do we retain source locations without causing poor debugging |
| // behavior? |
| if (!isa<CallInst>(I)) |
| I.setDebugLoc(DebugLoc()); |
| |
| if (isa<LoadInst>(I)) |
| ++NumMovedLoads; |
| else if (isa<CallInst>(I)) |
| ++NumMovedCalls; |
| ++NumHoisted; |
| return true; |
| } |
| |
| /// Only sink or hoist an instruction if it is not a trapping instruction, |
| /// or if the instruction is known not to trap when moved to the preheader. |
| /// or if it is a trapping instruction and is guaranteed to execute. |
| static bool isSafeToExecuteUnconditionally(Instruction &Inst, |
| const DominatorTree *DT, |
| const Loop *CurLoop, |
| const LoopSafetyInfo *SafetyInfo, |
| OptimizationRemarkEmitter *ORE, |
| const Instruction *CtxI) { |
| if (isSafeToSpeculativelyExecute(&Inst, CtxI, DT)) |
| return true; |
| |
| bool GuaranteedToExecute = |
| isGuaranteedToExecute(Inst, DT, CurLoop, SafetyInfo); |
| |
| if (!GuaranteedToExecute) { |
| auto *LI = dyn_cast<LoadInst>(&Inst); |
| if (LI && CurLoop->isLoopInvariant(LI->getPointerOperand())) |
| ORE->emit([&]() { |
| return OptimizationRemarkMissed( |
| DEBUG_TYPE, "LoadWithLoopInvariantAddressCondExecuted", LI) |
| << "failed to hoist load with loop-invariant address " |
| "because load is conditionally executed"; |
| }); |
| } |
| |
| return GuaranteedToExecute; |
| } |
| |
| namespace { |
| class LoopPromoter : public LoadAndStorePromoter { |
| Value *SomePtr; // Designated pointer to store to. |
| const SmallSetVector<Value *, 8> &PointerMustAliases; |
| SmallVectorImpl<BasicBlock *> &LoopExitBlocks; |
| SmallVectorImpl<Instruction *> &LoopInsertPts; |
| PredIteratorCache &PredCache; |
| AliasSetTracker &AST; |
| LoopInfo &LI; |
| DebugLoc DL; |
| int Alignment; |
| bool UnorderedAtomic; |
| AAMDNodes AATags; |
| |
| Value *maybeInsertLCSSAPHI(Value *V, BasicBlock *BB) const { |
| if (Instruction *I = dyn_cast<Instruction>(V)) |
| if (Loop *L = LI.getLoopFor(I->getParent())) |
| if (!L->contains(BB)) { |
| // We need to create an LCSSA PHI node for the incoming value and |
| // store that. |
| PHINode *PN = PHINode::Create(I->getType(), PredCache.size(BB), |
| I->getName() + ".lcssa", &BB->front()); |
| for (BasicBlock *Pred : PredCache.get(BB)) |
| PN->addIncoming(I, Pred); |
| return PN; |
| } |
| return V; |
| } |
| |
| public: |
| LoopPromoter(Value *SP, ArrayRef<const Instruction *> Insts, SSAUpdater &S, |
| const SmallSetVector<Value *, 8> &PMA, |
| SmallVectorImpl<BasicBlock *> &LEB, |
| SmallVectorImpl<Instruction *> &LIP, PredIteratorCache &PIC, |
| AliasSetTracker &ast, LoopInfo &li, DebugLoc dl, int alignment, |
| bool UnorderedAtomic, const AAMDNodes &AATags) |
| : LoadAndStorePromoter(Insts, S), SomePtr(SP), PointerMustAliases(PMA), |
| LoopExitBlocks(LEB), LoopInsertPts(LIP), PredCache(PIC), AST(ast), |
| LI(li), DL(std::move(dl)), Alignment(alignment), |
| UnorderedAtomic(UnorderedAtomic), AATags(AATags) {} |
| |
| bool isInstInList(Instruction *I, |
| const SmallVectorImpl<Instruction *> &) const override { |
| Value *Ptr; |
| if (LoadInst *LI = dyn_cast<LoadInst>(I)) |
| Ptr = LI->getOperand(0); |
| else |
| Ptr = cast<StoreInst>(I)->getPointerOperand(); |
| return PointerMustAliases.count(Ptr); |
| } |
| |
| void doExtraRewritesBeforeFinalDeletion() const override { |
| // Insert stores after in the loop exit blocks. Each exit block gets a |
| // store of the live-out values that feed them. Since we've already told |
| // the SSA updater about the defs in the loop and the preheader |
| // definition, it is all set and we can start using it. |
| for (unsigned i = 0, e = LoopExitBlocks.size(); i != e; ++i) { |
| BasicBlock *ExitBlock = LoopExitBlocks[i]; |
| Value *LiveInValue = SSA.GetValueInMiddleOfBlock(ExitBlock); |
| LiveInValue = maybeInsertLCSSAPHI(LiveInValue, ExitBlock); |
| Value *Ptr = maybeInsertLCSSAPHI(SomePtr, ExitBlock); |
| Instruction *InsertPos = LoopInsertPts[i]; |
| StoreInst *NewSI = new StoreInst(LiveInValue, Ptr, InsertPos); |
| if (UnorderedAtomic) |
| NewSI->setOrdering(AtomicOrdering::Unordered); |
| NewSI->setAlignment(Alignment); |
| NewSI->setDebugLoc(DL); |
| if (AATags) |
| NewSI->setAAMetadata(AATags); |
| } |
| } |
| |
| void replaceLoadWithValue(LoadInst *LI, Value *V) const override { |
| // Update alias analysis. |
| AST.copyValue(LI, V); |
| } |
| void instructionDeleted(Instruction *I) const override { AST.deleteValue(I); } |
| }; |
| |
| |
| /// Return true iff we can prove that a caller of this function can not inspect |
| /// the contents of the provided object in a well defined program. |
| bool isKnownNonEscaping(Value *Object, const TargetLibraryInfo *TLI) { |
| if (isa<AllocaInst>(Object)) |
| // Since the alloca goes out of scope, we know the caller can't retain a |
| // reference to it and be well defined. Thus, we don't need to check for |
| // capture. |
| return true; |
| |
| // For all other objects we need to know that the caller can't possibly |
| // have gotten a reference to the object. There are two components of |
| // that: |
| // 1) Object can't be escaped by this function. This is what |
| // PointerMayBeCaptured checks. |
| // 2) Object can't have been captured at definition site. For this, we |
| // need to know the return value is noalias. At the moment, we use a |
| // weaker condition and handle only AllocLikeFunctions (which are |
| // known to be noalias). TODO |
| return isAllocLikeFn(Object, TLI) && |
| !PointerMayBeCaptured(Object, true, true); |
| } |
| |
| } // namespace |
| |
| /// Try to promote memory values to scalars by sinking stores out of the |
| /// loop and moving loads to before the loop. We do this by looping over |
| /// the stores in the loop, looking for stores to Must pointers which are |
| /// loop invariant. |
| /// |
| bool llvm::promoteLoopAccessesToScalars( |
| const SmallSetVector<Value *, 8> &PointerMustAliases, |
| SmallVectorImpl<BasicBlock *> &ExitBlocks, |
| SmallVectorImpl<Instruction *> &InsertPts, PredIteratorCache &PIC, |
| LoopInfo *LI, DominatorTree *DT, const TargetLibraryInfo *TLI, |
| Loop *CurLoop, AliasSetTracker *CurAST, LoopSafetyInfo *SafetyInfo, |
| OptimizationRemarkEmitter *ORE) { |
| // Verify inputs. |
| assert(LI != nullptr && DT != nullptr && CurLoop != nullptr && |
| CurAST != nullptr && SafetyInfo != nullptr && |
| "Unexpected Input to promoteLoopAccessesToScalars"); |
| |
| Value *SomePtr = *PointerMustAliases.begin(); |
| BasicBlock *Preheader = CurLoop->getLoopPreheader(); |
| |
| // It is not safe to promote a load/store from the loop if the load/store is |
| // conditional. For example, turning: |
| // |
| // for () { if (c) *P += 1; } |
| // |
| // into: |
| // |
| // tmp = *P; for () { if (c) tmp +=1; } *P = tmp; |
| // |
| // is not safe, because *P may only be valid to access if 'c' is true. |
| // |
| // The safety property divides into two parts: |
| // p1) The memory may not be dereferenceable on entry to the loop. In this |
| // case, we can't insert the required load in the preheader. |
| // p2) The memory model does not allow us to insert a store along any dynamic |
| // path which did not originally have one. |
| // |
| // If at least one store is guaranteed to execute, both properties are |
| // satisfied, and promotion is legal. |
| // |
| // This, however, is not a necessary condition. Even if no store/load is |
| // guaranteed to execute, we can still establish these properties. |
| // We can establish (p1) by proving that hoisting the load into the preheader |
| // is safe (i.e. proving dereferenceability on all paths through the loop). We |
| // can use any access within the alias set to prove dereferenceability, |
| // since they're all must alias. |
| // |
| // There are two ways establish (p2): |
| // a) Prove the location is thread-local. In this case the memory model |
| // requirement does not apply, and stores are safe to insert. |
| // b) Prove a store dominates every exit block. In this case, if an exit |
| // blocks is reached, the original dynamic path would have taken us through |
| // the store, so inserting a store into the exit block is safe. Note that this |
| // is different from the store being guaranteed to execute. For instance, |
| // if an exception is thrown on the first iteration of the loop, the original |
| // store is never executed, but the exit blocks are not executed either. |
| |
| bool DereferenceableInPH = false; |
| bool SafeToInsertStore = false; |
| |
| SmallVector<Instruction *, 64> LoopUses; |
| |
| // We start with an alignment of one and try to find instructions that allow |
| // us to prove better alignment. |
| unsigned Alignment = 1; |
| // Keep track of which types of access we see |
| bool SawUnorderedAtomic = false; |
| bool SawNotAtomic = false; |
| AAMDNodes AATags; |
| |
| const DataLayout &MDL = Preheader->getModule()->getDataLayout(); |
| |
| bool IsKnownThreadLocalObject = false; |
| if (SafetyInfo->MayThrow) { |
| // If a loop can throw, we have to insert a store along each unwind edge. |
| // That said, we can't actually make the unwind edge explicit. Therefore, |
| // we have to prove that the store is dead along the unwind edge. We do |
| // this by proving that the caller can't have a reference to the object |
| // after return and thus can't possibly load from the object. |
| Value *Object = GetUnderlyingObject(SomePtr, MDL); |
| if (!isKnownNonEscaping(Object, TLI)) |
| return false; |
| // Subtlety: Alloca's aren't visible to callers, but *are* potentially |
| // visible to other threads if captured and used during their lifetimes. |
| IsKnownThreadLocalObject = !isa<AllocaInst>(Object); |
| } |
| |
| // Check that all of the pointers in the alias set have the same type. We |
| // cannot (yet) promote a memory location that is loaded and stored in |
| // different sizes. While we are at it, collect alignment and AA info. |
| for (Value *ASIV : PointerMustAliases) { |
| // Check that all of the pointers in the alias set have the same type. We |
| // cannot (yet) promote a memory location that is loaded and stored in |
| // different sizes. |
| if (SomePtr->getType() != ASIV->getType()) |
| return false; |
| |
| for (User *U : ASIV->users()) { |
| // Ignore instructions that are outside the loop. |
| Instruction *UI = dyn_cast<Instruction>(U); |
| if (!UI || !CurLoop->contains(UI)) |
| continue; |
| |
| // If there is an non-load/store instruction in the loop, we can't promote |
| // it. |
| if (LoadInst *Load = dyn_cast<LoadInst>(UI)) { |
| assert(!Load->isVolatile() && "AST broken"); |
| if (!Load->isUnordered()) |
| return false; |
| |
| SawUnorderedAtomic |= Load->isAtomic(); |
| SawNotAtomic |= !Load->isAtomic(); |
| |
| if (!DereferenceableInPH) |
| DereferenceableInPH = isSafeToExecuteUnconditionally( |
| *Load, DT, CurLoop, SafetyInfo, ORE, Preheader->getTerminator()); |
| } else if (const StoreInst *Store = dyn_cast<StoreInst>(UI)) { |
| // Stores *of* the pointer are not interesting, only stores *to* the |
| // pointer. |
| if (UI->getOperand(1) != ASIV) |
| continue; |
| assert(!Store->isVolatile() && "AST broken"); |
| if (!Store->isUnordered()) |
| return false; |
| |
| SawUnorderedAtomic |= Store->isAtomic(); |
| SawNotAtomic |= !Store->isAtomic(); |
| |
| // If the store is guaranteed to execute, both properties are satisfied. |
| // We may want to check if a store is guaranteed to execute even if we |
| // already know that promotion is safe, since it may have higher |
| // alignment than any other guaranteed stores, in which case we can |
| // raise the alignment on the promoted store. |
| unsigned InstAlignment = Store->getAlignment(); |
| if (!InstAlignment) |
| InstAlignment = |
| MDL.getABITypeAlignment(Store->getValueOperand()->getType()); |
| |
| if (!DereferenceableInPH || !SafeToInsertStore || |
| (InstAlignment > Alignment)) { |
| if (isGuaranteedToExecute(*UI, DT, CurLoop, SafetyInfo)) { |
| DereferenceableInPH = true; |
| SafeToInsertStore = true; |
| Alignment = std::max(Alignment, InstAlignment); |
| } |
| } |
| |
| // If a store dominates all exit blocks, it is safe to sink. |
| // As explained above, if an exit block was executed, a dominating |
| // store must have been executed at least once, so we are not |
| // introducing stores on paths that did not have them. |
| // Note that this only looks at explicit exit blocks. If we ever |
| // start sinking stores into unwind edges (see above), this will break. |
| if (!SafeToInsertStore) |
| SafeToInsertStore = llvm::all_of(ExitBlocks, [&](BasicBlock *Exit) { |
| return DT->dominates(Store->getParent(), Exit); |
| }); |
| |
| // If the store is not guaranteed to execute, we may still get |
| // deref info through it. |
| if (!DereferenceableInPH) { |
| DereferenceableInPH = isDereferenceableAndAlignedPointer( |
| Store->getPointerOperand(), Store->getAlignment(), MDL, |
| Preheader->getTerminator(), DT); |
| } |
| } else |
| return false; // Not a load or store. |
| |
| // Merge the AA tags. |
| if (LoopUses.empty()) { |
| // On the first load/store, just take its AA tags. |
| UI->getAAMetadata(AATags); |
| } else if (AATags) { |
| UI->getAAMetadata(AATags, /* Merge = */ true); |
| } |
| |
| LoopUses.push_back(UI); |
| } |
| } |
| |
| // If we found both an unordered atomic instruction and a non-atomic memory |
| // access, bail. We can't blindly promote non-atomic to atomic since we |
| // might not be able to lower the result. We can't downgrade since that |
| // would violate memory model. Also, align 0 is an error for atomics. |
| if (SawUnorderedAtomic && SawNotAtomic) |
| return false; |
| |
| // If we couldn't prove we can hoist the load, bail. |
| if (!DereferenceableInPH) |
| return false; |
| |
| // We know we can hoist the load, but don't have a guaranteed store. |
| // Check whether the location is thread-local. If it is, then we can insert |
| // stores along paths which originally didn't have them without violating the |
| // memory model. |
| if (!SafeToInsertStore) { |
| if (IsKnownThreadLocalObject) |
| SafeToInsertStore = true; |
| else { |
| Value *Object = GetUnderlyingObject(SomePtr, MDL); |
| SafeToInsertStore = |
| (isAllocLikeFn(Object, TLI) || isa<AllocaInst>(Object)) && |
| !PointerMayBeCaptured(Object, true, true); |
| } |
| } |
| |
| // If we've still failed to prove we can sink the store, give up. |
| if (!SafeToInsertStore) |
| return false; |
| |
| // Otherwise, this is safe to promote, lets do it! |
| LLVM_DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " << *SomePtr |
| << '\n'); |
| ORE->emit([&]() { |
| return OptimizationRemark(DEBUG_TYPE, "PromoteLoopAccessesToScalar", |
| LoopUses[0]) |
| << "Moving accesses to memory location out of the loop"; |
| }); |
| ++NumPromoted; |
| |
| // Grab a debug location for the inserted loads/stores; given that the |
| // inserted loads/stores have little relation to the original loads/stores, |
| // this code just arbitrarily picks a location from one, since any debug |
| // location is better than none. |
| DebugLoc DL = LoopUses[0]->getDebugLoc(); |
| |
| // We use the SSAUpdater interface to insert phi nodes as required. |
| SmallVector<PHINode *, 16> NewPHIs; |
| SSAUpdater SSA(&NewPHIs); |
| LoopPromoter Promoter(SomePtr, LoopUses, SSA, PointerMustAliases, ExitBlocks, |
| InsertPts, PIC, *CurAST, *LI, DL, Alignment, |
| SawUnorderedAtomic, AATags); |
| |
| // Set up the preheader to have a definition of the value. It is the live-out |
| // value from the preheader that uses in the loop will use. |
| LoadInst *PreheaderLoad = new LoadInst( |
| SomePtr, SomePtr->getName() + ".promoted", Preheader->getTerminator()); |
| if (SawUnorderedAtomic) |
| PreheaderLoad->setOrdering(AtomicOrdering::Unordered); |
| PreheaderLoad->setAlignment(Alignment); |
| PreheaderLoad->setDebugLoc(DL); |
| if (AATags) |
| PreheaderLoad->setAAMetadata(AATags); |
| SSA.AddAvailableValue(Preheader, PreheaderLoad); |
| |
| // Rewrite all the loads in the loop and remember all the definitions from |
| // stores in the loop. |
| Promoter.run(LoopUses); |
| |
| // If the SSAUpdater didn't use the load in the preheader, just zap it now. |
| if (PreheaderLoad->use_empty()) |
| PreheaderLoad->eraseFromParent(); |
| |
| return true; |
| } |
| |
| /// Returns an owning pointer to an alias set which incorporates aliasing info |
| /// from L and all subloops of L. |
| /// FIXME: In new pass manager, there is no helper function to handle loop |
| /// analysis such as cloneBasicBlockAnalysis, so the AST needs to be recomputed |
| /// from scratch for every loop. Hook up with the helper functions when |
| /// available in the new pass manager to avoid redundant computation. |
| AliasSetTracker * |
| LoopInvariantCodeMotion::collectAliasInfoForLoop(Loop *L, LoopInfo *LI, |
| AliasAnalysis *AA) { |
| AliasSetTracker *CurAST = nullptr; |
| SmallVector<Loop *, 4> RecomputeLoops; |
| for (Loop *InnerL : L->getSubLoops()) { |
| auto MapI = LoopToAliasSetMap.find(InnerL); |
| // If the AST for this inner loop is missing it may have been merged into |
| // some other loop's AST and then that loop unrolled, and so we need to |
| // recompute it. |
| if (MapI == LoopToAliasSetMap.end()) { |
| RecomputeLoops.push_back(InnerL); |
| continue; |
| } |
| AliasSetTracker *InnerAST = MapI->second; |
| |
| if (CurAST != nullptr) { |
| // What if InnerLoop was modified by other passes ? |
| CurAST->add(*InnerAST); |
| |
| // Once we've incorporated the inner loop's AST into ours, we don't need |
| // the subloop's anymore. |
| delete InnerAST; |
| } else { |
| CurAST = InnerAST; |
| } |
| LoopToAliasSetMap.erase(MapI); |
| } |
| if (CurAST == nullptr) |
| CurAST = new AliasSetTracker(*AA); |
| |
| auto mergeLoop = [&](Loop *L) { |
| // Loop over the body of this loop, looking for calls, invokes, and stores. |
| for (BasicBlock *BB : L->blocks()) |
| CurAST->add(*BB); // Incorporate the specified basic block |
| }; |
| |
| // Add everything from the sub loops that are no longer directly available. |
| for (Loop *InnerL : RecomputeLoops) |
| mergeLoop(InnerL); |
| |
| // And merge in this loop. |
| mergeLoop(L); |
| |
| return CurAST; |
| } |
| |
| /// Simple analysis hook. Clone alias set info. |
| /// |
| void LegacyLICMPass::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, |
| Loop *L) { |
| AliasSetTracker *AST = LICM.getLoopToAliasSetMap().lookup(L); |
| if (!AST) |
| return; |
| |
| AST->copyValue(From, To); |
| } |
| |
| /// Simple Analysis hook. Delete value V from alias set |
| /// |
| void LegacyLICMPass::deleteAnalysisValue(Value *V, Loop *L) { |
| AliasSetTracker *AST = LICM.getLoopToAliasSetMap().lookup(L); |
| if (!AST) |
| return; |
| |
| AST->deleteValue(V); |
| } |
| |
| /// Simple Analysis hook. Delete value L from alias set map. |
| /// |
| void LegacyLICMPass::deleteAnalysisLoop(Loop *L) { |
| AliasSetTracker *AST = LICM.getLoopToAliasSetMap().lookup(L); |
| if (!AST) |
| return; |
| |
| delete AST; |
| LICM.getLoopToAliasSetMap().erase(L); |
| } |
| |
| /// Return true if the body of this loop may store into the memory |
| /// location pointed to by V. |
| /// |
| static bool pointerInvalidatedByLoop(Value *V, uint64_t Size, |
| const AAMDNodes &AAInfo, |
| AliasSetTracker *CurAST) { |
| // Check to see if any of the basic blocks in CurLoop invalidate *V. |
| return CurAST->getAliasSetForPointer(V, Size, AAInfo).isMod(); |
| } |
| |
| /// Little predicate that returns true if the specified basic block is in |
| /// a subloop of the current one, not the current one itself. |
| /// |
| static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI) { |
| assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop"); |
| return LI->getLoopFor(BB) != CurLoop; |
| } |