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Diffstat (limited to 'contrib/llvm/lib/Transforms/Scalar/LICM.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Scalar/LICM.cpp | 1014 |
1 files changed, 1014 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/Scalar/LICM.cpp b/contrib/llvm/lib/Transforms/Scalar/LICM.cpp new file mode 100644 index 0000000..f0e6d64 --- /dev/null +++ b/contrib/llvm/lib/Transforms/Scalar/LICM.cpp @@ -0,0 +1,1014 @@ +//===-- 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.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/AliasSetTracker.h" +#include "llvm/Analysis/ConstantFolding.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/ScalarEvolution.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/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/Utils/Local.h" +#include "llvm/Transforms/Utils/LoopUtils.h" +#include "llvm/Transforms/Utils/SSAUpdater.h" +#include <algorithm> +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"); + +static cl::opt<bool> +DisablePromotion("disable-licm-promotion", cl::Hidden, + cl::desc("Disable memory promotion in LICM pass")); + +static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI); +static bool isNotUsedInLoop(const Instruction &I, const Loop *CurLoop); +static bool hoist(Instruction &I, BasicBlock *Preheader); +static bool sink(Instruction &I, const LoopInfo *LI, const DominatorTree *DT, + const Loop *CurLoop, AliasSetTracker *CurAST ); +static bool isGuaranteedToExecute(const Instruction &Inst, + const DominatorTree *DT, + const Loop *CurLoop, + const LICMSafetyInfo *SafetyInfo); +static bool isSafeToExecuteUnconditionally(const Instruction &Inst, + const DominatorTree *DT, + const TargetLibraryInfo *TLI, + const Loop *CurLoop, + const LICMSafetyInfo *SafetyInfo, + const Instruction *CtxI = nullptr); +static bool pointerInvalidatedByLoop(Value *V, uint64_t Size, + const AAMDNodes &AAInfo, + AliasSetTracker *CurAST); +static Instruction *CloneInstructionInExitBlock(const Instruction &I, + BasicBlock &ExitBlock, + PHINode &PN, + const LoopInfo *LI); +static bool canSinkOrHoistInst(Instruction &I, AliasAnalysis *AA, + DominatorTree *DT, TargetLibraryInfo *TLI, + Loop *CurLoop, AliasSetTracker *CurAST, + LICMSafetyInfo *SafetyInfo); + +namespace { + struct LICM : public LoopPass { + static char ID; // Pass identification, replacement for typeid + LICM() : LoopPass(ID) { + initializeLICMPass(*PassRegistry::getPassRegistry()); + } + + bool runOnLoop(Loop *L, LPPassManager &LPM) override; + + /// This transformation requires natural loop information & requires that + /// loop preheaders be inserted into the CFG... + /// + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.setPreservesCFG(); + AU.addRequired<DominatorTreeWrapperPass>(); + AU.addRequired<LoopInfoWrapperPass>(); + AU.addRequiredID(LoopSimplifyID); + AU.addPreservedID(LoopSimplifyID); + AU.addRequiredID(LCSSAID); + AU.addPreservedID(LCSSAID); + AU.addRequired<AliasAnalysis>(); + AU.addPreserved<AliasAnalysis>(); + AU.addPreserved<ScalarEvolution>(); + AU.addRequired<TargetLibraryInfoWrapperPass>(); + } + + using llvm::Pass::doFinalization; + + bool doFinalization() override { + assert(LoopToAliasSetMap.empty() && "Didn't free loop alias sets"); + return false; + } + + private: + AliasAnalysis *AA; // Current AliasAnalysis information + LoopInfo *LI; // Current LoopInfo + DominatorTree *DT; // Dominator Tree for the current Loop. + + TargetLibraryInfo *TLI; // TargetLibraryInfo for constant folding. + + // State that is updated as we process loops. + bool Changed; // Set to true when we change anything. + BasicBlock *Preheader; // The preheader block of the current loop... + Loop *CurLoop; // The current loop we are working on... + AliasSetTracker *CurAST; // AliasSet information for the current loop... + DenseMap<Loop*, AliasSetTracker*> LoopToAliasSetMap; + + /// 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; + }; +} + +char LICM::ID = 0; +INITIALIZE_PASS_BEGIN(LICM, "licm", "Loop Invariant Code Motion", false, false) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) +INITIALIZE_PASS_DEPENDENCY(LoopSimplify) +INITIALIZE_PASS_DEPENDENCY(LCSSA) +INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) +INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) +INITIALIZE_AG_DEPENDENCY(AliasAnalysis) +INITIALIZE_PASS_END(LICM, "licm", "Loop Invariant Code Motion", false, false) + +Pass *llvm::createLICMPass() { return new LICM(); } + +/// 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. +/// +bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) { + if (skipOptnoneFunction(L)) + return false; + + Changed = false; + + // Get our Loop and Alias Analysis information... + LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); + AA = &getAnalysis<AliasAnalysis>(); + DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); + + TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); + + assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form."); + + CurAST = new AliasSetTracker(*AA); + // Collect Alias info from subloops. + for (Loop::iterator LoopItr = L->begin(), LoopItrE = L->end(); + LoopItr != LoopItrE; ++LoopItr) { + Loop *InnerL = *LoopItr; + AliasSetTracker *InnerAST = LoopToAliasSetMap[InnerL]; + assert(InnerAST && "Where is my AST?"); + + // 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; + LoopToAliasSetMap.erase(InnerL); + } + + CurLoop = L; + + // Get the preheader block to move instructions into... + Preheader = L->getLoopPreheader(); + + // Loop over the body of this loop, looking for calls, invokes, and stores. + // Because subloops have already been incorporated into AST, we skip blocks in + // subloops. + // + for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); + I != E; ++I) { + BasicBlock *BB = *I; + if (LI->getLoopFor(BB) == L) // Ignore blocks in subloops. + CurAST->add(*BB); // Incorporate the specified basic block + } + + // Compute loop safety information. + LICMSafetyInfo SafetyInfo; + computeLICMSafetyInfo(&SafetyInfo, CurLoop); + + // 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, CurLoop, + CurAST, &SafetyInfo); + if (Preheader) + Changed |= hoistRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, + CurLoop, CurAST, &SafetyInfo); + + // Now that all loop invariants have been removed from the loop, promote any + // memory references to scalars that we can. + if (!DisablePromotion && (Preheader || L->hasDedicatedExits())) { + SmallVector<BasicBlock *, 8> ExitBlocks; + SmallVector<Instruction *, 8> InsertPts; + PredIteratorCache PIC; + + // Loop over all of the alias sets in the tracker object. + for (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end(); + I != E; ++I) + Changed |= promoteLoopAccessesToScalars(*I, ExitBlocks, InsertPts, + PIC, LI, DT, CurLoop, + CurAST, &SafetyInfo); + + // 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 (Changed) + formLCSSARecursively(*L, *DT, LI, + getAnalysisIfAvailable<ScalarEvolution>()); + } + + // 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!"); + + // Clear out loops state information for the next iteration + CurLoop = nullptr; + Preheader = nullptr; + + // If this loop is nested inside of another one, save the alias information + // for when we process the outer loop. + if (L->getParentLoop()) + LoopToAliasSetMap[L] = CurAST; + else + delete CurAST; + 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, Loop *CurLoop, + AliasSetTracker *CurAST, LICMSafetyInfo *SafetyInfo) { + + // Verify inputs. + assert(N != nullptr && AA != nullptr && LI != nullptr && + DT != nullptr && CurLoop != nullptr && CurAST != nullptr && + SafetyInfo != nullptr && "Unexpected input to sinkRegion"); + + // Set changed as false. + bool Changed = false; + // Get basic block + BasicBlock *BB = N->getBlock(); + // If this subregion is not in the top level loop at all, exit. + if (!CurLoop->contains(BB)) return Changed; + + // We are processing blocks in reverse dfo, so process children first. + const std::vector<DomTreeNode*> &Children = N->getChildren(); + for (unsigned i = 0, e = Children.size(); i != e; ++i) + Changed |= + sinkRegion(Children[i], AA, LI, DT, TLI, CurLoop, CurAST, SafetyInfo); + // 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)) return Changed; + + 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)) { + DEBUG(dbgs() << "LICM deleting dead inst: " << I << '\n'); + ++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. + // + if (isNotUsedInLoop(I, CurLoop) && + canSinkOrHoistInst(I, AA, DT, TLI, CurLoop, CurAST, SafetyInfo)) { + ++II; + Changed |= sink(I, LI, DT, CurLoop, CurAST); + } + } + 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, LICMSafetyInfo *SafetyInfo) { + // Verify inputs. + assert(N != nullptr && AA != nullptr && LI != nullptr && + DT != nullptr && CurLoop != nullptr && CurAST != nullptr && + SafetyInfo != nullptr && "Unexpected input to hoistRegion"); + // Set changed as false. + bool Changed = false; + // Get basic block + BasicBlock *BB = N->getBlock(); + // If this subregion is not in the top level loop at all, exit. + if (!CurLoop->contains(BB)) return Changed; + // 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)) + 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)) { + DEBUG(dbgs() << "LICM folding inst: " << I << " --> " << *C << '\n'); + CurAST->copyValue(&I, C); + CurAST->deleteValue(&I); + I.replaceAllUsesWith(C); + I.eraseFromParent(); + 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, TLI, CurLoop, CurAST, SafetyInfo) && + isSafeToExecuteUnconditionally(I, DT, TLI, CurLoop, SafetyInfo, + CurLoop->getLoopPreheader()->getTerminator())) + Changed |= hoist(I, CurLoop->getLoopPreheader()); + } + + const std::vector<DomTreeNode*> &Children = N->getChildren(); + for (unsigned i = 0, e = Children.size(); i != e; ++i) + Changed |= + hoistRegion(Children[i], AA, LI, DT, TLI, CurLoop, CurAST, SafetyInfo); + return Changed; +} + +/// Computes loop safety information, checks loop body & header +/// for the possiblity of may throw exception. +/// +void llvm::computeLICMSafetyInfo(LICMSafetyInfo * SafetyInfo, Loop * CurLoop) { + assert(CurLoop != nullptr && "CurLoop cant be null"); + BasicBlock *Header = CurLoop->getHeader(); + // Setting default safety values. + SafetyInfo->MayThrow = false; + SafetyInfo->HeaderMayThrow = false; + // Iterate over header and compute dafety info. + for (BasicBlock::iterator I = Header->begin(), E = Header->end(); + (I != E) && !SafetyInfo->HeaderMayThrow; ++I) + SafetyInfo->HeaderMayThrow |= I->mayThrow(); + + SafetyInfo->MayThrow = SafetyInfo->HeaderMayThrow; + // Iterate over loop instructions and compute safety info. + for (Loop::block_iterator BB = CurLoop->block_begin(), + BBE = CurLoop->block_end(); (BB != BBE) && !SafetyInfo->MayThrow ; ++BB) + for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); + (I != E) && !SafetyInfo->MayThrow; ++I) + SafetyInfo->MayThrow |= I->mayThrow(); +} + +/// canSinkOrHoistInst - Return true if the hoister and sinker can handle this +/// instruction. +/// +bool canSinkOrHoistInst(Instruction &I, AliasAnalysis *AA, DominatorTree *DT, + TargetLibraryInfo *TLI, Loop *CurLoop, + AliasSetTracker *CurAST, LICMSafetyInfo *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 hoist volatile/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; + + // Don't hoist loads which have may-aliased stores in loop. + uint64_t Size = 0; + if (LI->getType()->isSized()) + Size = AA->getTypeStoreSize(LI->getType()); + + AAMDNodes AAInfo; + LI->getAAMetadata(AAInfo); + + return !pointerInvalidatedByLoop(LI->getOperand(0), Size, AAInfo, CurAST); + } 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; + + // Handle simple cases by querying alias analysis. + AliasAnalysis::ModRefBehavior Behavior = AA->getModRefBehavior(CI); + if (Behavior == AliasAnalysis::DoesNotAccessMemory) + return true; + if (AliasAnalysis::onlyReadsMemory(Behavior)) { + // 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 (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end(); + I != E; ++I) { + AliasSet &AS = *I; + 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; + + // 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, TLI, 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 isTriviallyReplacablePHI(const PHINode &PN, const Instruction &I) { + for (const Value *IncValue : PN.incoming_values()) + if (IncValue != &I) + return false; + + return true; +} + +/// 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. +/// +static bool isNotUsedInLoop(const Instruction &I, const Loop *CurLoop) { + for (const User *U : I.users()) { + const Instruction *UI = cast<Instruction>(U); + if (const PHINode *PN = dyn_cast<PHINode>(UI)) { + // A PHI node where all of the incoming values are this instruction are + // special -- they can just be RAUW'ed with the instruction and thus + // don't require a use in the predecessor. This is a particular important + // special case because it is the pattern found in LCSSA form. + if (isTriviallyReplacablePHI(*PN, I)) { + if (CurLoop->contains(PN)) + return false; + else + continue; + } + + // Otherwise, PHI node uses occur in predecessor blocks if the incoming + // values. Check for such a use being inside the loop. + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) + if (PN->getIncomingValue(i) == &I) + if (CurLoop->contains(PN->getIncomingBlock(i))) + return false; + + continue; + } + + if (CurLoop->contains(UI)) + return false; + } + return true; +} + +static Instruction *CloneInstructionInExitBlock(const Instruction &I, + BasicBlock &ExitBlock, + PHINode &PN, + const LoopInfo *LI) { + Instruction *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.begin()); + for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) + OpPN->addIncoming(OInst, PN.getIncomingBlock(i)); + *OI = OpPN; + } + return New; +} + +/// 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, const LoopInfo *LI, const DominatorTree *DT, + const Loop *CurLoop, AliasSetTracker *CurAST ) { + DEBUG(dbgs() << "LICM sinking instruction: " << I << "\n"); + bool Changed = false; + if (isa<LoadInst>(I)) ++NumMovedLoads; + else if (isa<CallInst>(I)) ++NumMovedCalls; + ++NumSunk; + Changed = true; + +#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. + while (!I.use_empty()) { + Instruction *User = I.user_back(); + if (!DT->isReachableFromEntry(User->getParent())) { + User->replaceUsesOfWith(&I, UndefValue::get(I.getType())); + continue; + } + // The user must be a PHI node. + PHINode *PN = cast<PHINode>(User); + + BasicBlock *ExitBlock = PN->getParent(); + assert(ExitBlockSet.count(ExitBlock) && + "The LCSSA PHI is not in an exit block!"); + + Instruction *New; + auto It = SunkCopies.find(ExitBlock); + if (It != SunkCopies.end()) + New = It->second; + else + New = SunkCopies[ExitBlock] = + CloneInstructionInExitBlock(I, *ExitBlock, *PN, LI); + + PN->replaceAllUsesWith(New); + PN->eraseFromParent(); + } + + CurAST->deleteValue(&I); + I.eraseFromParent(); + 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, BasicBlock *Preheader) { + DEBUG(dbgs() << "LICM hoisting to " << Preheader->getName() << ": " + << I << "\n"); + // Move the new node to the Preheader, before its terminator. + I.moveBefore(Preheader->getTerminator()); + + 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(const Instruction &Inst, + const DominatorTree *DT, + const TargetLibraryInfo *TLI, + const Loop *CurLoop, + const LICMSafetyInfo *SafetyInfo, + const Instruction *CtxI) { + if (isSafeToSpeculativelyExecute(&Inst, CtxI, DT, TLI)) + return true; + + return isGuaranteedToExecute(Inst, DT, CurLoop, SafetyInfo); +} + +static bool isGuaranteedToExecute(const Instruction &Inst, + const DominatorTree *DT, + const Loop *CurLoop, + const LICMSafetyInfo * SafetyInfo) { + + // We have to check to make sure that the instruction dominates all + // of the exit blocks. If it doesn't, then there is a path out of the loop + // which does not execute this instruction, so we can't hoist it. + + // If the instruction is in the header block for the loop (which is very + // common), it is always guaranteed to dominate the exit blocks. Since this + // is a common case, and can save some work, check it now. + if (Inst.getParent() == CurLoop->getHeader()) + // If there's a throw in the header block, we can't guarantee we'll reach + // Inst. + return !SafetyInfo->HeaderMayThrow; + + // Somewhere in this loop there is an instruction which may throw and make us + // exit the loop. + if (SafetyInfo->MayThrow) + return false; + + // Get the exit blocks for the current loop. + SmallVector<BasicBlock*, 8> ExitBlocks; + CurLoop->getExitBlocks(ExitBlocks); + + // Verify that the block dominates each of the exit blocks of the loop. + for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) + if (!DT->dominates(Inst.getParent(), ExitBlocks[i])) + return false; + + // As a degenerate case, if the loop is statically infinite then we haven't + // proven anything since there are no exit blocks. + if (ExitBlocks.empty()) + return false; + + return true; +} + +namespace { + class LoopPromoter : public LoadAndStorePromoter { + Value *SomePtr; // Designated pointer to store to. + SmallPtrSetImpl<Value*> &PointerMustAliases; + SmallVectorImpl<BasicBlock*> &LoopExitBlocks; + SmallVectorImpl<Instruction*> &LoopInsertPts; + PredIteratorCache &PredCache; + AliasSetTracker &AST; + LoopInfo &LI; + DebugLoc DL; + int Alignment; + 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->begin()); + for (BasicBlock *Pred : PredCache.get(BB)) + PN->addIncoming(I, Pred); + return PN; + } + return V; + } + + public: + LoopPromoter(Value *SP, + ArrayRef<const Instruction *> Insts, + SSAUpdater &S, SmallPtrSetImpl<Value *> &PMA, + SmallVectorImpl<BasicBlock *> &LEB, + SmallVectorImpl<Instruction *> &LIP, PredIteratorCache &PIC, + AliasSetTracker &ast, LoopInfo &li, DebugLoc dl, int alignment, + const AAMDNodes &AATags) + : LoadAndStorePromoter(Insts, S), SomePtr(SP), PointerMustAliases(PMA), + LoopExitBlocks(LEB), LoopInsertPts(LIP), PredCache(PIC), AST(ast), + LI(li), DL(dl), Alignment(alignment), 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); + 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); + } + }; +} // end anon 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(AliasSet &AS, + SmallVectorImpl<BasicBlock*>&ExitBlocks, + SmallVectorImpl<Instruction*>&InsertPts, + PredIteratorCache &PIC, LoopInfo *LI, + DominatorTree *DT, Loop *CurLoop, + AliasSetTracker *CurAST, + LICMSafetyInfo * SafetyInfo) { + // Verify inputs. + assert(LI != nullptr && DT != nullptr && + CurLoop != nullptr && CurAST != nullptr && + SafetyInfo != nullptr && + "Unexpected Input to promoteLoopAccessesToScalars"); + // Initially set Changed status to false. + bool Changed = false; + // 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() || !CurLoop->isLoopInvariant(AS.begin()->getValue())) + return Changed; + + assert(!AS.empty() && + "Must alias set should have at least one pointer element in it!"); + + Value *SomePtr = AS.begin()->getValue(); + BasicBlock * Preheader = CurLoop->getLoopPreheader(); + + // It isn't 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. + // + // It is safe to promote P if all uses are direct load/stores and if at + // least one is guaranteed to be executed. + bool GuaranteedToExecute = false; + + SmallVector<Instruction*, 64> LoopUses; + SmallPtrSet<Value*, 4> PointerMustAliases; + + // We start with an alignment of one and try to find instructions that allow + // us to prove better alignment. + unsigned Alignment = 1; + AAMDNodes AATags; + bool HasDedicatedExits = CurLoop->hasDedicatedExits(); + + // 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 (AliasSet::iterator ASI = AS.begin(), E = AS.end(); ASI != E; ++ASI) { + Value *ASIV = ASI->getValue(); + PointerMustAliases.insert(ASIV); + + // 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 Changed; + + 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 (const LoadInst *load = dyn_cast<LoadInst>(UI)) { + assert(!load->isVolatile() && "AST broken"); + if (!load->isSimple()) + return Changed; + } 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->isSimple()) + return Changed; + // 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 (!HasDedicatedExits || !Preheader) + return Changed; + + // Note that we only check GuaranteedToExecute inside the store case + // so that we do not introduce stores where they did not exist before + // (which would break the LLVM concurrency model). + + // If the alignment of this instruction allows us to specify a more + // restrictive (and performant) alignment and if we are sure this + // instruction will be executed, update the alignment. + // Larger is better, with the exception of 0 being the best alignment. + unsigned InstAlignment = store->getAlignment(); + if ((InstAlignment > Alignment || InstAlignment == 0) && Alignment != 0) + if (isGuaranteedToExecute(*UI, DT, CurLoop, SafetyInfo)) { + GuaranteedToExecute = true; + Alignment = InstAlignment; + } + + if (!GuaranteedToExecute) + GuaranteedToExecute = isGuaranteedToExecute(*UI, DT, + CurLoop, SafetyInfo); + + } else + return Changed; // 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 there isn't a guaranteed-to-execute instruction, we can't promote. + if (!GuaranteedToExecute) + return Changed; + + // Otherwise, this is safe to promote, lets do it! + DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " <<*SomePtr<<'\n'); + Changed = true; + ++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(); + + // Figure out the loop exits and their insertion points, if this is the + // first promotion. + if (ExitBlocks.empty()) { + CurLoop->getUniqueExitBlocks(ExitBlocks); + InsertPts.resize(ExitBlocks.size()); + for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) + InsertPts[i] = ExitBlocks[i]->getFirstInsertionPt(); + } + + // 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, 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()); + 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 Changed; +} + +/// Simple Analysis hook. Clone alias set info. +/// +void LICM::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L) { + AliasSetTracker *AST = LoopToAliasSetMap.lookup(L); + if (!AST) + return; + + AST->copyValue(From, To); +} + +/// Simple Analysis hook. Delete value V from alias set +/// +void LICM::deleteAnalysisValue(Value *V, Loop *L) { + AliasSetTracker *AST = LoopToAliasSetMap.lookup(L); + if (!AST) + return; + + AST->deleteValue(V); +} + +/// Simple Analysis hook. Delete value L from alias set map. +/// +void LICM::deleteAnalysisLoop(Loop *L) { + AliasSetTracker *AST = LoopToAliasSetMap.lookup(L); + if (!AST) + return; + + delete AST; + LoopToAliasSetMap.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; +} + |
