| //===-- 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/BasicAliasAnalysis.h" |
| #include "llvm/Analysis/ConstantFolding.h" |
| #include "llvm/Analysis/GlobalsModRef.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/LoopPass.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/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<AAResultsWrapperPass>(); |
| AU.addPreserved<AAResultsWrapperPass>(); |
| AU.addPreserved<BasicAAWrapperPass>(); |
| AU.addPreserved<GlobalsAAWrapperPass>(); |
| AU.addPreserved<ScalarEvolutionWrapperPass>(); |
| AU.addPreserved<SCEVAAWrapperPass>(); |
| 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(ScalarEvolutionWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(BasicAAWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(SCEVAAWrapperPass) |
| 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<AAResultsWrapperPass>().getAAResults(); |
| 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) { |
| auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>(); |
| formLCSSARecursively(*L, *DT, LI, SEWP ? &SEWP->getSE() : nullptr); |
| } |
| } |
| |
| // 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 possibility 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 safety 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 = I.getModule()->getDataLayout().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. |
| FunctionModRefBehavior Behavior = AA->getModRefBehavior(CI); |
| if (Behavior == FMRB_DoesNotAccessMemory) |
| return true; |
| if (AliasAnalysis::onlyReadsMemory(Behavior)) { |
| // A readonly argmemonly function only reads from memory pointed to by |
| // it's arguments with arbitrary offsets. If we can prove there are no |
| // writes to this memory in the loop, we can hoist or sink. |
| if (AliasAnalysis::onlyAccessesArgPointees(Behavior)) { |
| for (Value *Op : CI->arg_operands()) |
| if (Op->getType()->isPointerTy() && |
| pointerInvalidatedByLoop(Op, MemoryLocation::UnknownSize, |
| AAMDNodes(), CurAST)) |
| return false; |
| return true; |
| } |
| // If this call only reads from memory and there are no writes to memory |
| // in the loop, we can hoist or sink the call as appropriate. |
| bool FoundMod = false; |
| for (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.front()); |
| 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()) { |
| Value::user_iterator UI = I.user_begin(); |
| auto *User = cast<Instruction>(*UI); |
| 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); |
| |
| // Surprisingly, instructions can be used outside of loops without any |
| // exits. This can only happen in PHI nodes if the incoming block is |
| // unreachable. |
| Use &U = UI.getUse(); |
| BasicBlock *BB = PN->getIncomingBlock(U); |
| if (!DT->isReachableFromEntry(BB)) { |
| U = UndefValue::get(I.getType()); |
| continue; |
| } |
| |
| 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()); |
| |
| // Metadata can be dependent on the condition we are hoisting above. |
| // Conservatively strip all metadata on the instruction. |
| I.dropUnknownNonDebugMetadata(); |
| |
| 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->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, 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; |
| } |
| |