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Diffstat (limited to 'llvm/lib/Transforms/Scalar/LICM.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Scalar/LICM.cpp | 2336 |
1 files changed, 2336 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp new file mode 100644 index 000000000000..6ce4831a7359 --- /dev/null +++ b/llvm/lib/Transforms/Scalar/LICM.cpp @@ -0,0 +1,2336 @@ +//===-- LICM.cpp - Loop Invariant Code Motion Pass ------------------------===// +// +// 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 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/SetOperations.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/GuardUtils.h" +#include "llvm/Analysis/Loads.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/LoopIterator.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/MemoryBuiltins.h" +#include "llvm/Analysis/MemorySSA.h" +#include "llvm/Analysis/MemorySSAUpdater.h" +#include "llvm/Analysis/OptimizationRemarkEmitter.h" +#include "llvm/Analysis/ScalarEvolution.h" +#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/CFG.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DebugInfoMetadata.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/PatternMatch.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/Local.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(NumCreatedBlocks, "Number of blocks created"); +STATISTIC(NumClonedBranches, "Number of branches cloned"); +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<bool> ControlFlowHoisting( + "licm-control-flow-hoisting", cl::Hidden, cl::init(false), + cl::desc("Enable control flow (and PHI) hoisting in LICM")); + +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)")); + +// Default value of zero implies we use the regular alias set tracker mechanism +// instead of the cross product using AA to identify aliasing of the memory +// location we are interested in. +static cl::opt<int> +LICMN2Theshold("licm-n2-threshold", cl::Hidden, cl::init(0), + cl::desc("How many instruction to cross product using AA")); + +// Experimental option to allow imprecision in LICM in pathological cases, in +// exchange for faster compile. This is to be removed if MemorySSA starts to +// address the same issue. This flag applies only when LICM uses MemorySSA +// instead on AliasSetTracker. LICM calls MemorySSAWalker's +// getClobberingMemoryAccess, up to the value of the Cap, getting perfect +// accuracy. Afterwards, LICM will call into MemorySSA's getDefiningAccess, +// which may not be precise, since optimizeUses is capped. The result is +// correct, but we may not get as "far up" as possible to get which access is +// clobbering the one queried. +cl::opt<unsigned> llvm::SetLicmMssaOptCap( + "licm-mssa-optimization-cap", cl::init(100), cl::Hidden, + cl::desc("Enable imprecision in LICM in pathological cases, in exchange " + "for faster compile. Caps the MemorySSA clobbering calls.")); + +// Experimentally, memory promotion carries less importance than sinking and +// hoisting. Limit when we do promotion when using MemorySSA, in order to save +// compile time. +cl::opt<unsigned> llvm::SetLicmMssaNoAccForPromotionCap( + "licm-mssa-max-acc-promotion", cl::init(250), cl::Hidden, + cl::desc("[LICM & MemorySSA] When MSSA in LICM is disabled, this has no " + "effect. When MSSA in LICM is enabled, then this is the maximum " + "number of accesses allowed to be present in a loop in order to " + "enable memory promotion.")); + +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 void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop, + BasicBlock *Dest, ICFLoopSafetyInfo *SafetyInfo, + MemorySSAUpdater *MSSAU, OptimizationRemarkEmitter *ORE); +static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT, + const Loop *CurLoop, ICFLoopSafetyInfo *SafetyInfo, + MemorySSAUpdater *MSSAU, OptimizationRemarkEmitter *ORE); +static bool isSafeToExecuteUnconditionally(Instruction &Inst, + const DominatorTree *DT, + const Loop *CurLoop, + const LoopSafetyInfo *SafetyInfo, + OptimizationRemarkEmitter *ORE, + const Instruction *CtxI = nullptr); +static bool pointerInvalidatedByLoop(MemoryLocation MemLoc, + AliasSetTracker *CurAST, Loop *CurLoop, + AliasAnalysis *AA); +static bool pointerInvalidatedByLoopWithMSSA(MemorySSA *MSSA, MemoryUse *MU, + Loop *CurLoop, + SinkAndHoistLICMFlags &Flags); +static Instruction *CloneInstructionInExitBlock( + Instruction &I, BasicBlock &ExitBlock, PHINode &PN, const LoopInfo *LI, + const LoopSafetyInfo *SafetyInfo, MemorySSAUpdater *MSSAU); + +static void eraseInstruction(Instruction &I, ICFLoopSafetyInfo &SafetyInfo, + AliasSetTracker *AST, MemorySSAUpdater *MSSAU); + +static void moveInstructionBefore(Instruction &I, Instruction &Dest, + ICFLoopSafetyInfo &SafetyInfo, + MemorySSAUpdater *MSSAU); + +namespace { +struct LoopInvariantCodeMotion { + using ASTrackerMapTy = DenseMap<Loop *, std::unique_ptr<AliasSetTracker>>; + bool runOnLoop(Loop *L, AliasAnalysis *AA, LoopInfo *LI, DominatorTree *DT, + TargetLibraryInfo *TLI, TargetTransformInfo *TTI, + ScalarEvolution *SE, MemorySSA *MSSA, + OptimizationRemarkEmitter *ORE, bool DeleteAST); + + ASTrackerMapTy &getLoopToAliasSetMap() { return LoopToAliasSetMap; } + LoopInvariantCodeMotion(unsigned LicmMssaOptCap, + unsigned LicmMssaNoAccForPromotionCap) + : LicmMssaOptCap(LicmMssaOptCap), + LicmMssaNoAccForPromotionCap(LicmMssaNoAccForPromotionCap) {} + +private: + ASTrackerMapTy LoopToAliasSetMap; + unsigned LicmMssaOptCap; + unsigned LicmMssaNoAccForPromotionCap; + + std::unique_ptr<AliasSetTracker> + collectAliasInfoForLoop(Loop *L, LoopInfo *LI, AliasAnalysis *AA); + std::unique_ptr<AliasSetTracker> + collectAliasInfoForLoopWithMSSA(Loop *L, AliasAnalysis *AA, + MemorySSAUpdater *MSSAU); +}; + +struct LegacyLICMPass : public LoopPass { + static char ID; // Pass identification, replacement for typeid + LegacyLICMPass( + unsigned LicmMssaOptCap = SetLicmMssaOptCap, + unsigned LicmMssaNoAccForPromotionCap = SetLicmMssaNoAccForPromotionCap) + : LoopPass(ID), LICM(LicmMssaOptCap, LicmMssaNoAccForPromotionCap) { + 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. + 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( + *L->getHeader()->getParent()), + &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.addPreserved<MemorySSAWrapperPass>(); + } + AU.addRequired<TargetTransformInfoWrapperPass>(); + getLoopAnalysisUsage(AU); + } + + using llvm::Pass::doFinalization; + + bool doFinalization() override { + auto &AliasSetMap = LICM.getLoopToAliasSetMap(); + // All loops in the AliasSetMap should be cleaned up already. The only case + // where we fail to do so is if an outer loop gets deleted before LICM + // visits it. + assert(all_of(AliasSetMap, + [](LoopInvariantCodeMotion::ASTrackerMapTy::value_type &KV) { + return !KV.first->getParentLoop(); + }) && + "Didn't free loop alias sets"); + AliasSetMap.clear(); + 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(LicmMssaOptCap, LicmMssaNoAccForPromotionCap); + 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>(); + if (AR.MSSA) + PA.preserve<MemorySSAAnalysis>(); + + 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(); } +Pass *llvm::createLICMPass(unsigned LicmMssaOptCap, + unsigned LicmMssaNoAccForPromotionCap) { + return new LegacyLICMPass(LicmMssaOptCap, LicmMssaNoAccForPromotionCap); +} + +/// 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."); + + // If this loop has metadata indicating that LICM is not to be performed then + // just exit. + if (hasDisableLICMTransformsHint(L)) { + return false; + } + + std::unique_ptr<AliasSetTracker> CurAST; + std::unique_ptr<MemorySSAUpdater> MSSAU; + bool NoOfMemAccTooLarge = false; + unsigned LicmMssaOptCounter = 0; + + if (!MSSA) { + LLVM_DEBUG(dbgs() << "LICM: Using Alias Set Tracker.\n"); + CurAST = collectAliasInfoForLoop(L, LI, AA); + } else { + LLVM_DEBUG(dbgs() << "LICM: Using MemorySSA.\n"); + MSSAU = std::make_unique<MemorySSAUpdater>(MSSA); + + unsigned AccessCapCount = 0; + for (auto *BB : L->getBlocks()) { + if (auto *Accesses = MSSA->getBlockAccesses(BB)) { + for (const auto &MA : *Accesses) { + (void)MA; + AccessCapCount++; + if (AccessCapCount > LicmMssaNoAccForPromotionCap) { + NoOfMemAccTooLarge = true; + break; + } + } + } + if (NoOfMemAccTooLarge) + break; + } + } + + // Get the preheader block to move instructions into... + BasicBlock *Preheader = L->getLoopPreheader(); + + // Compute loop safety information. + ICFLoopSafetyInfo SafetyInfo(DT); + SafetyInfo.computeLoopSafetyInfo(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. + SinkAndHoistLICMFlags Flags = {NoOfMemAccTooLarge, LicmMssaOptCounter, + LicmMssaOptCap, LicmMssaNoAccForPromotionCap, + /*IsSink=*/true}; + if (L->hasDedicatedExits()) + Changed |= sinkRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, TTI, L, + CurAST.get(), MSSAU.get(), &SafetyInfo, Flags, ORE); + Flags.IsSink = false; + if (Preheader) + Changed |= hoistRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, L, + CurAST.get(), MSSAU.get(), &SafetyInfo, Flags, 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() && + !NoOfMemAccTooLarge) { + // 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; + SmallVector<MemoryAccess *, 8> MSSAInsertPts; + InsertPts.reserve(ExitBlocks.size()); + if (MSSAU) + MSSAInsertPts.reserve(ExitBlocks.size()); + for (BasicBlock *ExitBlock : ExitBlocks) { + InsertPts.push_back(&*ExitBlock->getFirstInsertionPt()); + if (MSSAU) + MSSAInsertPts.push_back(nullptr); + } + + PredIteratorCache PIC; + + bool Promoted = false; + + // Build an AST using MSSA. + if (!CurAST.get()) + CurAST = collectAliasInfoForLoopWithMSSA(L, AA, MSSAU.get()); + + // 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() || + !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, MSSAInsertPts, PIC, LI, + DT, TLI, L, CurAST.get(), MSSAU.get(), &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 (!MSSAU.get() && CurAST.get() && L->getParentLoop() && !DeleteAST) + LoopToAliasSetMap[L] = std::move(CurAST); + + if (MSSAU.get() && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + 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, MemorySSAUpdater *MSSAU, + ICFLoopSafetyInfo *SafetyInfo, + SinkAndHoistLICMFlags &Flags, + OptimizationRemarkEmitter *ORE) { + + // Verify inputs. + assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr && + CurLoop != nullptr && SafetyInfo != nullptr && + "Unexpected input to sinkRegion."); + assert(((CurAST != nullptr) ^ (MSSAU != nullptr)) && + "Either AliasSetTracker or MemorySSA should be initialized."); + + // 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; + eraseInstruction(I, *SafetyInfo, CurAST, MSSAU); + 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, MSSAU, true, &Flags, + ORE) && + !I.mayHaveSideEffects()) { + if (sink(I, LI, DT, CurLoop, SafetyInfo, MSSAU, ORE)) { + if (!FreeInLoop) { + ++II; + eraseInstruction(I, *SafetyInfo, CurAST, MSSAU); + } + Changed = true; + } + } + } + } + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + return Changed; +} + +namespace { +// This is a helper class for hoistRegion to make it able to hoist control flow +// in order to be able to hoist phis. The way this works is that we initially +// start hoisting to the loop preheader, and when we see a loop invariant branch +// we make note of this. When we then come to hoist an instruction that's +// conditional on such a branch we duplicate the branch and the relevant control +// flow, then hoist the instruction into the block corresponding to its original +// block in the duplicated control flow. +class ControlFlowHoister { +private: + // Information about the loop we are hoisting from + LoopInfo *LI; + DominatorTree *DT; + Loop *CurLoop; + MemorySSAUpdater *MSSAU; + + // A map of blocks in the loop to the block their instructions will be hoisted + // to. + DenseMap<BasicBlock *, BasicBlock *> HoistDestinationMap; + + // The branches that we can hoist, mapped to the block that marks a + // convergence point of their control flow. + DenseMap<BranchInst *, BasicBlock *> HoistableBranches; + +public: + ControlFlowHoister(LoopInfo *LI, DominatorTree *DT, Loop *CurLoop, + MemorySSAUpdater *MSSAU) + : LI(LI), DT(DT), CurLoop(CurLoop), MSSAU(MSSAU) {} + + void registerPossiblyHoistableBranch(BranchInst *BI) { + // We can only hoist conditional branches with loop invariant operands. + if (!ControlFlowHoisting || !BI->isConditional() || + !CurLoop->hasLoopInvariantOperands(BI)) + return; + + // The branch destinations need to be in the loop, and we don't gain + // anything by duplicating conditional branches with duplicate successors, + // as it's essentially the same as an unconditional branch. + BasicBlock *TrueDest = BI->getSuccessor(0); + BasicBlock *FalseDest = BI->getSuccessor(1); + if (!CurLoop->contains(TrueDest) || !CurLoop->contains(FalseDest) || + TrueDest == FalseDest) + return; + + // We can hoist BI if one branch destination is the successor of the other, + // or both have common successor which we check by seeing if the + // intersection of their successors is non-empty. + // TODO: This could be expanded to allowing branches where both ends + // eventually converge to a single block. + SmallPtrSet<BasicBlock *, 4> TrueDestSucc, FalseDestSucc; + TrueDestSucc.insert(succ_begin(TrueDest), succ_end(TrueDest)); + FalseDestSucc.insert(succ_begin(FalseDest), succ_end(FalseDest)); + BasicBlock *CommonSucc = nullptr; + if (TrueDestSucc.count(FalseDest)) { + CommonSucc = FalseDest; + } else if (FalseDestSucc.count(TrueDest)) { + CommonSucc = TrueDest; + } else { + set_intersect(TrueDestSucc, FalseDestSucc); + // If there's one common successor use that. + if (TrueDestSucc.size() == 1) + CommonSucc = *TrueDestSucc.begin(); + // If there's more than one pick whichever appears first in the block list + // (we can't use the value returned by TrueDestSucc.begin() as it's + // unpredicatable which element gets returned). + else if (!TrueDestSucc.empty()) { + Function *F = TrueDest->getParent(); + auto IsSucc = [&](BasicBlock &BB) { return TrueDestSucc.count(&BB); }; + auto It = std::find_if(F->begin(), F->end(), IsSucc); + assert(It != F->end() && "Could not find successor in function"); + CommonSucc = &*It; + } + } + // The common successor has to be dominated by the branch, as otherwise + // there will be some other path to the successor that will not be + // controlled by this branch so any phi we hoist would be controlled by the + // wrong condition. This also takes care of avoiding hoisting of loop back + // edges. + // TODO: In some cases this could be relaxed if the successor is dominated + // by another block that's been hoisted and we can guarantee that the + // control flow has been replicated exactly. + if (CommonSucc && DT->dominates(BI, CommonSucc)) + HoistableBranches[BI] = CommonSucc; + } + + bool canHoistPHI(PHINode *PN) { + // The phi must have loop invariant operands. + if (!ControlFlowHoisting || !CurLoop->hasLoopInvariantOperands(PN)) + return false; + // We can hoist phis if the block they are in is the target of hoistable + // branches which cover all of the predecessors of the block. + SmallPtrSet<BasicBlock *, 8> PredecessorBlocks; + BasicBlock *BB = PN->getParent(); + for (BasicBlock *PredBB : predecessors(BB)) + PredecessorBlocks.insert(PredBB); + // If we have less predecessor blocks than predecessors then the phi will + // have more than one incoming value for the same block which we can't + // handle. + // TODO: This could be handled be erasing some of the duplicate incoming + // values. + if (PredecessorBlocks.size() != pred_size(BB)) + return false; + for (auto &Pair : HoistableBranches) { + if (Pair.second == BB) { + // Which blocks are predecessors via this branch depends on if the + // branch is triangle-like or diamond-like. + if (Pair.first->getSuccessor(0) == BB) { + PredecessorBlocks.erase(Pair.first->getParent()); + PredecessorBlocks.erase(Pair.first->getSuccessor(1)); + } else if (Pair.first->getSuccessor(1) == BB) { + PredecessorBlocks.erase(Pair.first->getParent()); + PredecessorBlocks.erase(Pair.first->getSuccessor(0)); + } else { + PredecessorBlocks.erase(Pair.first->getSuccessor(0)); + PredecessorBlocks.erase(Pair.first->getSuccessor(1)); + } + } + } + // PredecessorBlocks will now be empty if for every predecessor of BB we + // found a hoistable branch source. + return PredecessorBlocks.empty(); + } + + BasicBlock *getOrCreateHoistedBlock(BasicBlock *BB) { + if (!ControlFlowHoisting) + return CurLoop->getLoopPreheader(); + // If BB has already been hoisted, return that + if (HoistDestinationMap.count(BB)) + return HoistDestinationMap[BB]; + + // Check if this block is conditional based on a pending branch + auto HasBBAsSuccessor = + [&](DenseMap<BranchInst *, BasicBlock *>::value_type &Pair) { + return BB != Pair.second && (Pair.first->getSuccessor(0) == BB || + Pair.first->getSuccessor(1) == BB); + }; + auto It = std::find_if(HoistableBranches.begin(), HoistableBranches.end(), + HasBBAsSuccessor); + + // If not involved in a pending branch, hoist to preheader + BasicBlock *InitialPreheader = CurLoop->getLoopPreheader(); + if (It == HoistableBranches.end()) { + LLVM_DEBUG(dbgs() << "LICM using " << InitialPreheader->getName() + << " as hoist destination for " << BB->getName() + << "\n"); + HoistDestinationMap[BB] = InitialPreheader; + return InitialPreheader; + } + BranchInst *BI = It->first; + assert(std::find_if(++It, HoistableBranches.end(), HasBBAsSuccessor) == + HoistableBranches.end() && + "BB is expected to be the target of at most one branch"); + + LLVMContext &C = BB->getContext(); + BasicBlock *TrueDest = BI->getSuccessor(0); + BasicBlock *FalseDest = BI->getSuccessor(1); + BasicBlock *CommonSucc = HoistableBranches[BI]; + BasicBlock *HoistTarget = getOrCreateHoistedBlock(BI->getParent()); + + // Create hoisted versions of blocks that currently don't have them + auto CreateHoistedBlock = [&](BasicBlock *Orig) { + if (HoistDestinationMap.count(Orig)) + return HoistDestinationMap[Orig]; + BasicBlock *New = + BasicBlock::Create(C, Orig->getName() + ".licm", Orig->getParent()); + HoistDestinationMap[Orig] = New; + DT->addNewBlock(New, HoistTarget); + if (CurLoop->getParentLoop()) + CurLoop->getParentLoop()->addBasicBlockToLoop(New, *LI); + ++NumCreatedBlocks; + LLVM_DEBUG(dbgs() << "LICM created " << New->getName() + << " as hoist destination for " << Orig->getName() + << "\n"); + return New; + }; + BasicBlock *HoistTrueDest = CreateHoistedBlock(TrueDest); + BasicBlock *HoistFalseDest = CreateHoistedBlock(FalseDest); + BasicBlock *HoistCommonSucc = CreateHoistedBlock(CommonSucc); + + // Link up these blocks with branches. + if (!HoistCommonSucc->getTerminator()) { + // The new common successor we've generated will branch to whatever that + // hoist target branched to. + BasicBlock *TargetSucc = HoistTarget->getSingleSuccessor(); + assert(TargetSucc && "Expected hoist target to have a single successor"); + HoistCommonSucc->moveBefore(TargetSucc); + BranchInst::Create(TargetSucc, HoistCommonSucc); + } + if (!HoistTrueDest->getTerminator()) { + HoistTrueDest->moveBefore(HoistCommonSucc); + BranchInst::Create(HoistCommonSucc, HoistTrueDest); + } + if (!HoistFalseDest->getTerminator()) { + HoistFalseDest->moveBefore(HoistCommonSucc); + BranchInst::Create(HoistCommonSucc, HoistFalseDest); + } + + // If BI is being cloned to what was originally the preheader then + // HoistCommonSucc will now be the new preheader. + if (HoistTarget == InitialPreheader) { + // Phis in the loop header now need to use the new preheader. + InitialPreheader->replaceSuccessorsPhiUsesWith(HoistCommonSucc); + if (MSSAU) + MSSAU->wireOldPredecessorsToNewImmediatePredecessor( + HoistTarget->getSingleSuccessor(), HoistCommonSucc, {HoistTarget}); + // The new preheader dominates the loop header. + DomTreeNode *PreheaderNode = DT->getNode(HoistCommonSucc); + DomTreeNode *HeaderNode = DT->getNode(CurLoop->getHeader()); + DT->changeImmediateDominator(HeaderNode, PreheaderNode); + // The preheader hoist destination is now the new preheader, with the + // exception of the hoist destination of this branch. + for (auto &Pair : HoistDestinationMap) + if (Pair.second == InitialPreheader && Pair.first != BI->getParent()) + Pair.second = HoistCommonSucc; + } + + // Now finally clone BI. + ReplaceInstWithInst( + HoistTarget->getTerminator(), + BranchInst::Create(HoistTrueDest, HoistFalseDest, BI->getCondition())); + ++NumClonedBranches; + + assert(CurLoop->getLoopPreheader() && + "Hoisting blocks should not have destroyed preheader"); + return HoistDestinationMap[BB]; + } +}; +} // namespace + +/// 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, MemorySSAUpdater *MSSAU, + ICFLoopSafetyInfo *SafetyInfo, + SinkAndHoistLICMFlags &Flags, + OptimizationRemarkEmitter *ORE) { + // Verify inputs. + assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr && + CurLoop != nullptr && SafetyInfo != nullptr && + "Unexpected input to hoistRegion."); + assert(((CurAST != nullptr) ^ (MSSAU != nullptr)) && + "Either AliasSetTracker or MemorySSA should be initialized."); + + ControlFlowHoister CFH(LI, DT, CurLoop, MSSAU); + + // Keep track of instructions that have been hoisted, as they may need to be + // re-hoisted if they end up not dominating all of their uses. + SmallVector<Instruction *, 16> HoistedInstructions; + + // For PHI hoisting to work we need to hoist blocks before their successors. + // We can do this by iterating through the blocks in the loop in reverse + // post-order. + LoopBlocksRPO Worklist(CurLoop); + Worklist.perform(LI); + bool Changed = false; + for (BasicBlock *BB : Worklist) { + // 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->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'); + if (CurAST) + CurAST->copyValue(&I, C); + // FIXME MSSA: Such replacements may make accesses unoptimized (D51960). + I.replaceAllUsesWith(C); + if (isInstructionTriviallyDead(&I, TLI)) + eraseInstruction(I, *SafetyInfo, CurAST, MSSAU); + 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. + // TODO: It may be safe to hoist if we are hoisting to a conditional block + // and we have accurately duplicated the control flow from the loop header + // to that block. + if (CurLoop->hasLoopInvariantOperands(&I) && + canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, MSSAU, true, &Flags, + ORE) && + isSafeToExecuteUnconditionally( + I, DT, CurLoop, SafetyInfo, ORE, + CurLoop->getLoopPreheader()->getTerminator())) { + hoist(I, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo, + MSSAU, ORE); + HoistedInstructions.push_back(&I); + Changed = true; + 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()); + SafetyInfo->insertInstructionTo(ReciprocalDivisor, I.getParent()); + ReciprocalDivisor->insertBefore(&I); + + auto Product = + BinaryOperator::CreateFMul(I.getOperand(0), ReciprocalDivisor); + Product->setFastMathFlags(I.getFastMathFlags()); + SafetyInfo->insertInstructionTo(Product, I.getParent()); + Product->insertAfter(&I); + I.replaceAllUsesWith(Product); + eraseInstruction(I, *SafetyInfo, CurAST, MSSAU); + + hoist(*ReciprocalDivisor, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), + SafetyInfo, MSSAU, ORE); + HoistedInstructions.push_back(ReciprocalDivisor); + Changed = true; + continue; + } + + auto IsInvariantStart = [&](Instruction &I) { + using namespace PatternMatch; + return I.use_empty() && + match(&I, m_Intrinsic<Intrinsic::invariant_start>()); + }; + auto MustExecuteWithoutWritesBefore = [&](Instruction &I) { + return SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop) && + SafetyInfo->doesNotWriteMemoryBefore(I, CurLoop); + }; + if ((IsInvariantStart(I) || isGuard(&I)) && + CurLoop->hasLoopInvariantOperands(&I) && + MustExecuteWithoutWritesBefore(I)) { + hoist(I, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo, + MSSAU, ORE); + HoistedInstructions.push_back(&I); + Changed = true; + continue; + } + + if (PHINode *PN = dyn_cast<PHINode>(&I)) { + if (CFH.canHoistPHI(PN)) { + // Redirect incoming blocks first to ensure that we create hoisted + // versions of those blocks before we hoist the phi. + for (unsigned int i = 0; i < PN->getNumIncomingValues(); ++i) + PN->setIncomingBlock( + i, CFH.getOrCreateHoistedBlock(PN->getIncomingBlock(i))); + hoist(*PN, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo, + MSSAU, ORE); + assert(DT->dominates(PN, BB) && "Conditional PHIs not expected"); + Changed = true; + continue; + } + } + + // Remember possibly hoistable branches so we can actually hoist them + // later if needed. + if (BranchInst *BI = dyn_cast<BranchInst>(&I)) + CFH.registerPossiblyHoistableBranch(BI); + } + } + + // If we hoisted instructions to a conditional block they may not dominate + // their uses that weren't hoisted (such as phis where some operands are not + // loop invariant). If so make them unconditional by moving them to their + // immediate dominator. We iterate through the instructions in reverse order + // which ensures that when we rehoist an instruction we rehoist its operands, + // and also keep track of where in the block we are rehoisting to to make sure + // that we rehoist instructions before the instructions that use them. + Instruction *HoistPoint = nullptr; + if (ControlFlowHoisting) { + for (Instruction *I : reverse(HoistedInstructions)) { + if (!llvm::all_of(I->uses(), + [&](Use &U) { return DT->dominates(I, U); })) { + BasicBlock *Dominator = + DT->getNode(I->getParent())->getIDom()->getBlock(); + if (!HoistPoint || !DT->dominates(HoistPoint->getParent(), Dominator)) { + if (HoistPoint) + assert(DT->dominates(Dominator, HoistPoint->getParent()) && + "New hoist point expected to dominate old hoist point"); + HoistPoint = Dominator->getTerminator(); + } + LLVM_DEBUG(dbgs() << "LICM rehoisting to " + << HoistPoint->getParent()->getName() + << ": " << *I << "\n"); + moveInstructionBefore(*I, *HoistPoint, *SafetyInfo, MSSAU); + HoistPoint = I; + Changed = true; + } + } + } + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + // Now that we've finished hoisting make sure that LI and DT are still + // valid. +#ifdef EXPENSIVE_CHECKS + if (Changed) { + assert(DT->verify(DominatorTree::VerificationLevel::Fast) && + "Dominator tree verification failed"); + LI->verify(*DT); + } +#endif + + 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(LI->getType()); + + // 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; +} + +namespace { +/// Return true if-and-only-if we know how to (mechanically) both hoist and +/// sink a given instruction out of a loop. Does not address legality +/// concerns such as aliasing or speculation safety. +bool isHoistableAndSinkableInst(Instruction &I) { + // Only these instructions are hoistable/sinkable. + return (isa<LoadInst>(I) || isa<StoreInst>(I) || isa<CallInst>(I) || + isa<FenceInst>(I) || isa<CastInst>(I) || + isa<UnaryOperator>(I) || isa<BinaryOperator>(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 true if all of the alias sets within this AST are known not to +/// contain a Mod, or if MSSA knows thare are no MemoryDefs in the loop. +bool isReadOnly(AliasSetTracker *CurAST, const MemorySSAUpdater *MSSAU, + const Loop *L) { + if (CurAST) { + for (AliasSet &AS : *CurAST) { + if (!AS.isForwardingAliasSet() && AS.isMod()) { + return false; + } + } + return true; + } else { /*MSSAU*/ + for (auto *BB : L->getBlocks()) + if (MSSAU->getMemorySSA()->getBlockDefs(BB)) + return false; + return true; + } +} + +/// Return true if I is the only Instruction with a MemoryAccess in L. +bool isOnlyMemoryAccess(const Instruction *I, const Loop *L, + const MemorySSAUpdater *MSSAU) { + for (auto *BB : L->getBlocks()) + if (auto *Accs = MSSAU->getMemorySSA()->getBlockAccesses(BB)) { + int NotAPhi = 0; + for (const auto &Acc : *Accs) { + if (isa<MemoryPhi>(&Acc)) + continue; + const auto *MUD = cast<MemoryUseOrDef>(&Acc); + if (MUD->getMemoryInst() != I || NotAPhi++ == 1) + return false; + } + } + return true; +} +} + +bool llvm::canSinkOrHoistInst(Instruction &I, AAResults *AA, DominatorTree *DT, + Loop *CurLoop, AliasSetTracker *CurAST, + MemorySSAUpdater *MSSAU, + bool TargetExecutesOncePerLoop, + SinkAndHoistLICMFlags *Flags, + OptimizationRemarkEmitter *ORE) { + // If we don't understand the instruction, bail early. + if (!isHoistableAndSinkableInst(I)) + return false; + + MemorySSA *MSSA = MSSAU ? MSSAU->getMemorySSA() : nullptr; + if (MSSA) + assert(Flags != nullptr && "Flags cannot be null."); + + // 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->hasMetadata(LLVMContext::MD_invariant_load)) + return true; + + if (LI->isAtomic() && !TargetExecutesOncePerLoop) + return false; // Don't risk duplicating unordered loads + + // This checks for an invariant.start dominating the load. + if (isLoadInvariantInLoop(LI, DT, CurLoop)) + return true; + + bool Invalidated; + if (CurAST) + Invalidated = pointerInvalidatedByLoop(MemoryLocation::get(LI), CurAST, + CurLoop, AA); + else + Invalidated = pointerInvalidatedByLoopWithMSSA( + MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(LI)), CurLoop, *Flags); + // 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; + + using namespace PatternMatch; + if (match(CI, m_Intrinsic<Intrinsic::assume>())) + // Assumes don't actually alias anything or throw + return true; + + // 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)) { + // TODO: expand to writeable arguments + for (Value *Op : CI->arg_operands()) + if (Op->getType()->isPointerTy()) { + bool Invalidated; + if (CurAST) + Invalidated = pointerInvalidatedByLoop( + MemoryLocation(Op, LocationSize::unknown(), AAMDNodes()), + CurAST, CurLoop, AA); + else + Invalidated = pointerInvalidatedByLoopWithMSSA( + MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(CI)), CurLoop, + *Flags); + if (Invalidated) + 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. + if (isReadOnly(CurAST, MSSAU, CurLoop)) + return true; + } + + // FIXME: This should use mod/ref information to see if we can hoist or + // sink the call. + + return false; + } else if (auto *FI = dyn_cast<FenceInst>(&I)) { + // Fences alias (most) everything to provide ordering. For the moment, + // just give up if there are any other memory operations in the loop. + if (CurAST) { + auto Begin = CurAST->begin(); + assert(Begin != CurAST->end() && "must contain FI"); + if (std::next(Begin) != CurAST->end()) + // constant memory for instance, TODO: handle better + return false; + auto *UniqueI = Begin->getUniqueInstruction(); + if (!UniqueI) + // other memory op, give up + return false; + (void)FI; // suppress unused variable warning + assert(UniqueI == FI && "AS must contain FI"); + return true; + } else // MSSAU + return isOnlyMemoryAccess(FI, CurLoop, MSSAU); + } else if (auto *SI = dyn_cast<StoreInst>(&I)) { + if (!SI->isUnordered()) + return false; // Don't sink/hoist volatile or ordered atomic store! + + // We can only hoist a store that we can prove writes a value which is not + // read or overwritten within the loop. For those cases, we fallback to + // load store promotion instead. TODO: We can extend this to cases where + // there is exactly one write to the location and that write dominates an + // arbitrary number of reads in the loop. + if (CurAST) { + auto &AS = CurAST->getAliasSetFor(MemoryLocation::get(SI)); + + if (AS.isRef() || !AS.isMustAlias()) + // Quick exit test, handled by the full path below as well. + return false; + auto *UniqueI = AS.getUniqueInstruction(); + if (!UniqueI) + // other memory op, give up + return false; + assert(UniqueI == SI && "AS must contain SI"); + return true; + } else { // MSSAU + if (isOnlyMemoryAccess(SI, CurLoop, MSSAU)) + return true; + // If there are more accesses than the Promotion cap, give up, we're not + // walking a list that long. + if (Flags->NoOfMemAccTooLarge) + return false; + // Check store only if there's still "quota" to check clobber. + if (Flags->LicmMssaOptCounter >= Flags->LicmMssaOptCap) + return false; + // If there are interfering Uses (i.e. their defining access is in the + // loop), or ordered loads (stored as Defs!), don't move this store. + // Could do better here, but this is conservatively correct. + // TODO: Cache set of Uses on the first walk in runOnLoop, update when + // moving accesses. Can also extend to dominating uses. + auto *SIMD = MSSA->getMemoryAccess(SI); + for (auto *BB : CurLoop->getBlocks()) + if (auto *Accesses = MSSA->getBlockAccesses(BB)) { + for (const auto &MA : *Accesses) + if (const auto *MU = dyn_cast<MemoryUse>(&MA)) { + auto *MD = MU->getDefiningAccess(); + if (!MSSA->isLiveOnEntryDef(MD) && + CurLoop->contains(MD->getBlock())) + return false; + // Disable hoisting past potentially interfering loads. Optimized + // Uses may point to an access outside the loop, as getClobbering + // checks the previous iteration when walking the backedge. + // FIXME: More precise: no Uses that alias SI. + if (!Flags->IsSink && !MSSA->dominates(SIMD, MU)) + return false; + } else if (const auto *MD = dyn_cast<MemoryDef>(&MA)) { + if (auto *LI = dyn_cast<LoadInst>(MD->getMemoryInst())) { + (void)LI; // Silence warning. + assert(!LI->isUnordered() && "Expected unordered load"); + return false; + } + // Any call, while it may not be clobbering SI, it may be a use. + if (auto *CI = dyn_cast<CallInst>(MD->getMemoryInst())) { + // Check if the call may read from the memory locattion written + // to by SI. Check CI's attributes and arguments; the number of + // such checks performed is limited above by NoOfMemAccTooLarge. + ModRefInfo MRI = AA->getModRefInfo(CI, MemoryLocation::get(SI)); + if (isModOrRefSet(MRI)) + return false; + } + } + } + + auto *Source = MSSA->getSkipSelfWalker()->getClobberingMemoryAccess(SI); + Flags->LicmMssaOptCounter++; + // If there are no clobbering Defs in the loop, store is safe to hoist. + return MSSA->isLiveOnEntryDef(Source) || + !CurLoop->contains(Source->getBlock()); + } + } + + assert(!I.mayReadOrWriteMemory() && "unhandled aliasing"); + + // We've established mechanical ability and aliasing, it's up to the caller + // to check fault safety + return true; +} + +/// 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->getBlockColors(); + 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, MemorySSAUpdater *MSSAU) { + Instruction *New; + if (auto *CI = dyn_cast<CallInst>(&I)) { + const auto &BlockColors = SafetyInfo->getBlockColors(); + + // Sinking call-sites need to be handled differently from other + // instructions. The cloned call-site needs a funclet bundle operand + // appropriate for its 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"); + + if (MSSAU && MSSAU->getMemorySSA()->getMemoryAccess(&I)) { + // Create a new MemoryAccess and let MemorySSA set its defining access. + MemoryAccess *NewMemAcc = MSSAU->createMemoryAccessInBB( + New, nullptr, New->getParent(), MemorySSA::Beginning); + if (NewMemAcc) { + if (auto *MemDef = dyn_cast<MemoryDef>(NewMemAcc)) + MSSAU->insertDef(MemDef, /*RenameUses=*/true); + else { + auto *MemUse = cast<MemoryUse>(NewMemAcc); + MSSAU->insertUse(MemUse, /*RenameUses=*/true); + } + } + } + + // 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 void eraseInstruction(Instruction &I, ICFLoopSafetyInfo &SafetyInfo, + AliasSetTracker *AST, MemorySSAUpdater *MSSAU) { + if (AST) + AST->deleteValue(&I); + if (MSSAU) + MSSAU->removeMemoryAccess(&I); + SafetyInfo.removeInstruction(&I); + I.eraseFromParent(); +} + +static void moveInstructionBefore(Instruction &I, Instruction &Dest, + ICFLoopSafetyInfo &SafetyInfo, + MemorySSAUpdater *MSSAU) { + SafetyInfo.removeInstruction(&I); + SafetyInfo.insertInstructionTo(&I, Dest.getParent()); + I.moveBefore(&Dest); + if (MSSAU) + if (MemoryUseOrDef *OldMemAcc = cast_or_null<MemoryUseOrDef>( + MSSAU->getMemorySSA()->getMemoryAccess(&I))) + MSSAU->moveToPlace(OldMemAcc, Dest.getParent(), MemorySSA::End); +} + +static Instruction *sinkThroughTriviallyReplaceablePHI( + PHINode *TPN, Instruction *I, LoopInfo *LI, + SmallDenseMap<BasicBlock *, Instruction *, 32> &SunkCopies, + const LoopSafetyInfo *SafetyInfo, const Loop *CurLoop, + MemorySSAUpdater *MSSAU) { + 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, MSSAU); + 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->getBlockColors().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, + MemorySSAUpdater *MSSAU) { +#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] + // + const auto &BlockColors = SafetyInfo->getBlockColors(); + 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, MSSAU, 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. + SafetyInfo->copyColors(NewPred, PredBB); + } + 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, ICFLoopSafetyInfo *SafetyInfo, + MemorySSAUpdater *MSSAU, OptimizationRemarkEmitter *ORE) { + 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 + // unreachable blocks with undef and make all user PHIs trivially replaceable. + 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, MSSAU); + + // 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, MSSAU); + PN->replaceAllUsesWith(New); + eraseInstruction(*PN, *SafetyInfo, nullptr, nullptr); + 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 void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop, + BasicBlock *Dest, ICFLoopSafetyInfo *SafetyInfo, + MemorySSAUpdater *MSSAU, OptimizationRemarkEmitter *ORE) { + LLVM_DEBUG(dbgs() << "LICM hoisting to " << Dest->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. + !SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop)) + I.dropUnknownNonDebugMetadata(); + + if (isa<PHINode>(I)) + // Move the new node to the end of the phi list in the destination block. + moveInstructionBefore(I, *Dest->getFirstNonPHI(), *SafetyInfo, MSSAU); + else + // Move the new node to the destination block, before its terminator. + moveInstructionBefore(I, *Dest->getTerminator(), *SafetyInfo, MSSAU); + + // Apply line 0 debug locations when we are moving instructions to different + // basic blocks because we want to avoid jumpy line tables. + if (const DebugLoc &DL = I.getDebugLoc()) + I.setDebugLoc(DebugLoc::get(0, 0, DL.getScope(), DL.getInlinedAt())); + + if (isa<LoadInst>(I)) + ++NumMovedLoads; + else if (isa<CallInst>(I)) + ++NumMovedCalls; + ++NumHoisted; +} + +/// 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 = + SafetyInfo->isGuaranteedToExecute(Inst, DT, CurLoop); + + 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; + SmallVectorImpl<MemoryAccess *> &MSSAInsertPts; + PredIteratorCache &PredCache; + AliasSetTracker &AST; + MemorySSAUpdater *MSSAU; + LoopInfo &LI; + DebugLoc DL; + int Alignment; + bool UnorderedAtomic; + AAMDNodes AATags; + ICFLoopSafetyInfo &SafetyInfo; + + 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, + SmallVectorImpl<MemoryAccess *> &MSSAIP, PredIteratorCache &PIC, + AliasSetTracker &ast, MemorySSAUpdater *MSSAU, LoopInfo &li, + DebugLoc dl, int alignment, bool UnorderedAtomic, + const AAMDNodes &AATags, ICFLoopSafetyInfo &SafetyInfo) + : LoadAndStorePromoter(Insts, S), SomePtr(SP), PointerMustAliases(PMA), + LoopExitBlocks(LEB), LoopInsertPts(LIP), MSSAInsertPts(MSSAIP), + PredCache(PIC), AST(ast), MSSAU(MSSAU), LI(li), DL(std::move(dl)), + Alignment(alignment), UnorderedAtomic(UnorderedAtomic), AATags(AATags), + SafetyInfo(SafetyInfo) {} + + 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() 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(MaybeAlign(Alignment)); + NewSI->setDebugLoc(DL); + if (AATags) + NewSI->setAAMetadata(AATags); + + if (MSSAU) { + MemoryAccess *MSSAInsertPoint = MSSAInsertPts[i]; + MemoryAccess *NewMemAcc; + if (!MSSAInsertPoint) { + NewMemAcc = MSSAU->createMemoryAccessInBB( + NewSI, nullptr, NewSI->getParent(), MemorySSA::Beginning); + } else { + NewMemAcc = + MSSAU->createMemoryAccessAfter(NewSI, nullptr, MSSAInsertPoint); + } + MSSAInsertPts[i] = NewMemAcc; + MSSAU->insertDef(cast<MemoryDef>(NewMemAcc), true); + // FIXME: true for safety, false may still be correct. + } + } + } + + void replaceLoadWithValue(LoadInst *LI, Value *V) const override { + // Update alias analysis. + AST.copyValue(LI, V); + } + void instructionDeleted(Instruction *I) const override { + SafetyInfo.removeInstruction(I); + AST.deleteValue(I); + if (MSSAU) + MSSAU->removeMemoryAccess(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, + SmallVectorImpl<MemoryAccess *> &MSSAInsertPts, PredIteratorCache &PIC, + LoopInfo *LI, DominatorTree *DT, const TargetLibraryInfo *TLI, + Loop *CurLoop, AliasSetTracker *CurAST, MemorySSAUpdater *MSSAU, + ICFLoopSafetyInfo *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->anyBlockMayThrow()) { + // 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)) { + if (!Load->isUnordered()) + return false; + + SawUnorderedAtomic |= Load->isAtomic(); + SawNotAtomic |= !Load->isAtomic(); + + unsigned InstAlignment = Load->getAlignment(); + if (!InstAlignment) + InstAlignment = + MDL.getABITypeAlignment(Load->getType()); + + // Note that proving a load safe to speculate requires proving + // sufficient alignment at the target location. Proving it guaranteed + // to execute does as well. Thus we can increase our guaranteed + // alignment as well. + if (!DereferenceableInPH || (InstAlignment > Alignment)) + if (isSafeToExecuteUnconditionally(*Load, DT, CurLoop, SafetyInfo, + ORE, Preheader->getTerminator())) { + DereferenceableInPH = true; + Alignment = std::max(Alignment, InstAlignment); + } + } 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; + 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 (SafetyInfo->isGuaranteedToExecute(*UI, DT, CurLoop)) { + 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->getValueOperand()->getType(), + MaybeAlign(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're inserting an atomic load in the preheader, we must be able to + // lower it. We're only guaranteed to be able to lower naturally aligned + // atomics. + auto *SomePtrElemType = SomePtr->getType()->getPointerElementType(); + if (SawUnorderedAtomic && + Alignment < MDL.getTypeStoreSize(SomePtrElemType)) + 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, MSSAInsertPts, PIC, *CurAST, MSSAU, *LI, DL, + Alignment, SawUnorderedAtomic, AATags, *SafetyInfo); + + // 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->getType()->getPointerElementType(), SomePtr, + SomePtr->getName() + ".promoted", Preheader->getTerminator()); + if (SawUnorderedAtomic) + PreheaderLoad->setOrdering(AtomicOrdering::Unordered); + PreheaderLoad->setAlignment(MaybeAlign(Alignment)); + PreheaderLoad->setDebugLoc(DL); + if (AATags) + PreheaderLoad->setAAMetadata(AATags); + SSA.AddAvailableValue(Preheader, PreheaderLoad); + + if (MSSAU) { + MemoryAccess *PreheaderLoadMemoryAccess = MSSAU->createMemoryAccessInBB( + PreheaderLoad, nullptr, PreheaderLoad->getParent(), MemorySSA::End); + MemoryUse *NewMemUse = cast<MemoryUse>(PreheaderLoadMemoryAccess); + MSSAU->insertUse(NewMemUse, /*RenameUses=*/true); + } + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + // Rewrite all the loads in the loop and remember all the definitions from + // stores in the loop. + Promoter.run(LoopUses); + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + // If the SSAUpdater didn't use the load in the preheader, just zap it now. + if (PreheaderLoad->use_empty()) + eraseInstruction(*PreheaderLoad, *SafetyInfo, CurAST, MSSAU); + + 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. +std::unique_ptr<AliasSetTracker> +LoopInvariantCodeMotion::collectAliasInfoForLoop(Loop *L, LoopInfo *LI, + AliasAnalysis *AA) { + std::unique_ptr<AliasSetTracker> CurAST; + 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; + } + std::unique_ptr<AliasSetTracker> InnerAST = std::move(MapI->second); + + if (CurAST) { + // What if InnerLoop was modified by other passes ? + // Once we've incorporated the inner loop's AST into ours, we don't need + // the subloop's anymore. + CurAST->add(*InnerAST); + } else { + CurAST = std::move(InnerAST); + } + LoopToAliasSetMap.erase(MapI); + } + if (!CurAST) + CurAST = std::make_unique<AliasSetTracker>(*AA); + + // Add everything from the sub loops that are no longer directly available. + for (Loop *InnerL : RecomputeLoops) + for (BasicBlock *BB : InnerL->blocks()) + CurAST->add(*BB); + + // And merge in this loop (without anything from inner loops). + for (BasicBlock *BB : L->blocks()) + if (LI->getLoopFor(BB) == L) + CurAST->add(*BB); + + return CurAST; +} + +std::unique_ptr<AliasSetTracker> +LoopInvariantCodeMotion::collectAliasInfoForLoopWithMSSA( + Loop *L, AliasAnalysis *AA, MemorySSAUpdater *MSSAU) { + auto *MSSA = MSSAU->getMemorySSA(); + auto CurAST = std::make_unique<AliasSetTracker>(*AA, MSSA, L); + CurAST->addAllInstructionsInLoopUsingMSSA(); + return CurAST; +} + +/// Simple analysis hook. Clone alias set info. +/// +void LegacyLICMPass::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, + Loop *L) { + auto ASTIt = LICM.getLoopToAliasSetMap().find(L); + if (ASTIt == LICM.getLoopToAliasSetMap().end()) + return; + + ASTIt->second->copyValue(From, To); +} + +/// Simple Analysis hook. Delete value V from alias set +/// +void LegacyLICMPass::deleteAnalysisValue(Value *V, Loop *L) { + auto ASTIt = LICM.getLoopToAliasSetMap().find(L); + if (ASTIt == LICM.getLoopToAliasSetMap().end()) + return; + + ASTIt->second->deleteValue(V); +} + +/// Simple Analysis hook. Delete value L from alias set map. +/// +void LegacyLICMPass::deleteAnalysisLoop(Loop *L) { + if (!LICM.getLoopToAliasSetMap().count(L)) + return; + + LICM.getLoopToAliasSetMap().erase(L); +} + +static bool pointerInvalidatedByLoop(MemoryLocation MemLoc, + AliasSetTracker *CurAST, Loop *CurLoop, + AliasAnalysis *AA) { + // First check to see if any of the basic blocks in CurLoop invalidate *V. + bool isInvalidatedAccordingToAST = CurAST->getAliasSetFor(MemLoc).isMod(); + + if (!isInvalidatedAccordingToAST || !LICMN2Theshold) + return isInvalidatedAccordingToAST; + + // Check with a diagnostic analysis if we can refine the information above. + // This is to identify the limitations of using the AST. + // The alias set mechanism used by LICM has a major weakness in that it + // combines all things which may alias into a single set *before* asking + // modref questions. As a result, a single readonly call within a loop will + // collapse all loads and stores into a single alias set and report + // invalidation if the loop contains any store. For example, readonly calls + // with deopt states have this form and create a general alias set with all + // loads and stores. In order to get any LICM in loops containing possible + // deopt states we need a more precise invalidation of checking the mod ref + // info of each instruction within the loop and LI. This has a complexity of + // O(N^2), so currently, it is used only as a diagnostic tool since the + // default value of LICMN2Threshold is zero. + + // Don't look at nested loops. + if (CurLoop->begin() != CurLoop->end()) + return true; + + int N = 0; + for (BasicBlock *BB : CurLoop->getBlocks()) + for (Instruction &I : *BB) { + if (N >= LICMN2Theshold) { + LLVM_DEBUG(dbgs() << "Alasing N2 threshold exhausted for " + << *(MemLoc.Ptr) << "\n"); + return true; + } + N++; + auto Res = AA->getModRefInfo(&I, MemLoc); + if (isModSet(Res)) { + LLVM_DEBUG(dbgs() << "Aliasing failed on " << I << " for " + << *(MemLoc.Ptr) << "\n"); + return true; + } + } + LLVM_DEBUG(dbgs() << "Aliasing okay for " << *(MemLoc.Ptr) << "\n"); + return false; +} + +static bool pointerInvalidatedByLoopWithMSSA(MemorySSA *MSSA, MemoryUse *MU, + Loop *CurLoop, + SinkAndHoistLICMFlags &Flags) { + // For hoisting, use the walker to determine safety + if (!Flags.IsSink) { + MemoryAccess *Source; + // See declaration of SetLicmMssaOptCap for usage details. + if (Flags.LicmMssaOptCounter >= Flags.LicmMssaOptCap) + Source = MU->getDefiningAccess(); + else { + Source = MSSA->getSkipSelfWalker()->getClobberingMemoryAccess(MU); + Flags.LicmMssaOptCounter++; + } + return !MSSA->isLiveOnEntryDef(Source) && + CurLoop->contains(Source->getBlock()); + } + + // For sinking, we'd need to check all Defs below this use. The getClobbering + // call will look on the backedge of the loop, but will check aliasing with + // the instructions on the previous iteration. + // For example: + // for (i ... ) + // load a[i] ( Use (LoE) + // store a[i] ( 1 = Def (2), with 2 = Phi for the loop. + // i++; + // The load sees no clobbering inside the loop, as the backedge alias check + // does phi translation, and will check aliasing against store a[i-1]. + // However sinking the load outside the loop, below the store is incorrect. + + // For now, only sink if there are no Defs in the loop, and the existing ones + // precede the use and are in the same block. + // FIXME: Increase precision: Safe to sink if Use post dominates the Def; + // needs PostDominatorTreeAnalysis. + // FIXME: More precise: no Defs that alias this Use. + if (Flags.NoOfMemAccTooLarge) + return true; + for (auto *BB : CurLoop->getBlocks()) + if (auto *Accesses = MSSA->getBlockDefs(BB)) + for (const auto &MA : *Accesses) + if (const auto *MD = dyn_cast<MemoryDef>(&MA)) + if (MU->getBlock() != MD->getBlock() || + !MSSA->locallyDominates(MD, MU)) + return true; + return false; +} + +/// 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; +} |