| //===- IVUsers.cpp - Induction Variable Users -------------------*- C++ -*-===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements bookkeeping for "interesting" users of expressions |
| // computed from induction variables. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Analysis/IVUsers.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/Analysis/AssumptionCache.h" |
| #include "llvm/Analysis/CodeMetrics.h" |
| #include "llvm/Analysis/LoopAnalysisManager.h" |
| #include "llvm/Analysis/LoopPass.h" |
| #include "llvm/Analysis/ScalarEvolutionExpressions.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/Config/llvm-config.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/Module.h" |
| #include "llvm/IR/Type.h" |
| #include "llvm/InitializePasses.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include <algorithm> |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "iv-users" |
| |
| AnalysisKey IVUsersAnalysis::Key; |
| |
| IVUsers IVUsersAnalysis::run(Loop &L, LoopAnalysisManager &AM, |
| LoopStandardAnalysisResults &AR) { |
| return IVUsers(&L, &AR.AC, &AR.LI, &AR.DT, &AR.SE); |
| } |
| |
| char IVUsersWrapperPass::ID = 0; |
| INITIALIZE_PASS_BEGIN(IVUsersWrapperPass, "iv-users", |
| "Induction Variable Users", false, true) |
| INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) |
| INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass) |
| INITIALIZE_PASS_END(IVUsersWrapperPass, "iv-users", "Induction Variable Users", |
| false, true) |
| |
| Pass *llvm::createIVUsersPass() { return new IVUsersWrapperPass(); } |
| |
| /// isInteresting - Test whether the given expression is "interesting" when |
| /// used by the given expression, within the context of analyzing the |
| /// given loop. |
| static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L, |
| ScalarEvolution *SE, LoopInfo *LI) { |
| // An addrec is interesting if it's affine or if it has an interesting start. |
| if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) { |
| // Keep things simple. Don't touch loop-variant strides unless they're |
| // only used outside the loop and we can simplify them. |
| if (AR->getLoop() == L) |
| return AR->isAffine() || |
| (!L->contains(I) && |
| SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR); |
| // Otherwise recurse to see if the start value is interesting, and that |
| // the step value is not interesting, since we don't yet know how to |
| // do effective SCEV expansions for addrecs with interesting steps. |
| return isInteresting(AR->getStart(), I, L, SE, LI) && |
| !isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI); |
| } |
| |
| // An add is interesting if exactly one of its operands is interesting. |
| if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { |
| bool AnyInterestingYet = false; |
| for (const auto *Op : Add->operands()) |
| if (isInteresting(Op, I, L, SE, LI)) { |
| if (AnyInterestingYet) |
| return false; |
| AnyInterestingYet = true; |
| } |
| return AnyInterestingYet; |
| } |
| |
| // Nothing else is interesting here. |
| return false; |
| } |
| |
| /// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression |
| /// and now we need to decide whether the user should use the preinc or post-inc |
| /// value. If this user should use the post-inc version of the IV, return true. |
| /// |
| /// Choosing wrong here can break dominance properties (if we choose to use the |
| /// post-inc value when we cannot) or it can end up adding extra live-ranges to |
| /// the loop, resulting in reg-reg copies (if we use the pre-inc value when we |
| /// should use the post-inc value). |
| static bool IVUseShouldUsePostIncValue(Instruction *User, Value *Operand, |
| const Loop *L, DominatorTree *DT) { |
| // If the user is in the loop, use the preinc value. |
| if (L->contains(User)) |
| return false; |
| |
| BasicBlock *LatchBlock = L->getLoopLatch(); |
| if (!LatchBlock) |
| return false; |
| |
| // Ok, the user is outside of the loop. If it is dominated by the latch |
| // block, use the post-inc value. |
| if (DT->dominates(LatchBlock, User->getParent())) |
| return true; |
| |
| // There is one case we have to be careful of: PHI nodes. These little guys |
| // can live in blocks that are not dominated by the latch block, but (since |
| // their uses occur in the predecessor block, not the block the PHI lives in) |
| // should still use the post-inc value. Check for this case now. |
| PHINode *PN = dyn_cast<PHINode>(User); |
| if (!PN || !Operand) |
| return false; // not a phi, not dominated by latch block. |
| |
| // Look at all of the uses of Operand by the PHI node. If any use corresponds |
| // to a block that is not dominated by the latch block, give up and use the |
| // preincremented value. |
| for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) |
| if (PN->getIncomingValue(i) == Operand && |
| !DT->dominates(LatchBlock, PN->getIncomingBlock(i))) |
| return false; |
| |
| // Okay, all uses of Operand by PN are in predecessor blocks that really are |
| // dominated by the latch block. Use the post-incremented value. |
| return true; |
| } |
| |
| /// Inspect the specified instruction. If it is a reducible SCEV, recursively |
| /// add its users to the IVUsesByStride set and return true. Otherwise, return |
| /// false. |
| bool IVUsers::AddUsersIfInteresting(Instruction *I) { |
| const DataLayout &DL = I->getModule()->getDataLayout(); |
| |
| // Add this IV user to the Processed set before returning false to ensure that |
| // all IV users are members of the set. See IVUsers::isIVUserOrOperand. |
| if (!Processed.insert(I).second) |
| return true; // Instruction already handled. |
| |
| if (!SE->isSCEVable(I->getType())) |
| return false; // Void and FP expressions cannot be reduced. |
| |
| // IVUsers is used by LSR which assumes that all SCEV expressions are safe to |
| // pass to SCEVExpander. Expressions are not safe to expand if they represent |
| // operations that are not safe to speculate, namely integer division. |
| if (!isa<PHINode>(I) && !isSafeToSpeculativelyExecute(I)) |
| return false; |
| |
| // LSR is not APInt clean, do not touch integers bigger than 64-bits. |
| // Also avoid creating IVs of non-native types. For example, we don't want a |
| // 64-bit IV in 32-bit code just because the loop has one 64-bit cast. |
| uint64_t Width = SE->getTypeSizeInBits(I->getType()); |
| if (Width > 64 || !DL.isLegalInteger(Width)) |
| return false; |
| |
| // Don't attempt to promote ephemeral values to indvars. They will be removed |
| // later anyway. |
| if (EphValues.count(I)) |
| return false; |
| |
| // Get the symbolic expression for this instruction. |
| const SCEV *ISE = SE->getSCEV(I); |
| |
| // If we've come to an uninteresting expression, stop the traversal and |
| // call this a user. |
| if (!isInteresting(ISE, I, L, SE, LI)) |
| return false; |
| |
| SmallPtrSet<Instruction *, 4> UniqueUsers; |
| for (Use &U : I->uses()) { |
| Instruction *User = cast<Instruction>(U.getUser()); |
| if (!UniqueUsers.insert(User).second) |
| continue; |
| |
| // Do not infinitely recurse on PHI nodes. |
| if (isa<PHINode>(User) && Processed.count(User)) |
| continue; |
| |
| // Descend recursively, but not into PHI nodes outside the current loop. |
| // It's important to see the entire expression outside the loop to get |
| // choices that depend on addressing mode use right, although we won't |
| // consider references outside the loop in all cases. |
| // If User is already in Processed, we don't want to recurse into it again, |
| // but do want to record a second reference in the same instruction. |
| bool AddUserToIVUsers = false; |
| if (LI->getLoopFor(User->getParent()) != L) { |
| if (isa<PHINode>(User) || Processed.count(User) || |
| !AddUsersIfInteresting(User)) { |
| LLVM_DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n' |
| << " OF SCEV: " << *ISE << '\n'); |
| AddUserToIVUsers = true; |
| } |
| } else if (Processed.count(User) || !AddUsersIfInteresting(User)) { |
| LLVM_DEBUG(dbgs() << "FOUND USER: " << *User << '\n' |
| << " OF SCEV: " << *ISE << '\n'); |
| AddUserToIVUsers = true; |
| } |
| |
| if (AddUserToIVUsers) { |
| // Okay, we found a user that we cannot reduce. |
| IVStrideUse &NewUse = AddUser(User, I); |
| // Autodetect the post-inc loop set, populating NewUse.PostIncLoops. |
| // The regular return value here is discarded; instead of recording |
| // it, we just recompute it when we need it. |
| const SCEV *OriginalISE = ISE; |
| |
| auto NormalizePred = [&](const SCEVAddRecExpr *AR) { |
| auto *L = AR->getLoop(); |
| bool Result = IVUseShouldUsePostIncValue(User, I, L, DT); |
| if (Result) |
| NewUse.PostIncLoops.insert(L); |
| return Result; |
| }; |
| |
| ISE = normalizeForPostIncUseIf(ISE, NormalizePred, *SE); |
| |
| // PostIncNormalization effectively simplifies the expression under |
| // pre-increment assumptions. Those assumptions (no wrapping) might not |
| // hold for the post-inc value. Catch such cases by making sure the |
| // transformation is invertible. |
| if (OriginalISE != ISE) { |
| const SCEV *DenormalizedISE = |
| denormalizeForPostIncUse(ISE, NewUse.PostIncLoops, *SE); |
| |
| // If we normalized the expression, but denormalization doesn't give the |
| // original one, discard this user. |
| if (OriginalISE != DenormalizedISE) { |
| LLVM_DEBUG(dbgs() |
| << " DISCARDING (NORMALIZATION ISN'T INVERTIBLE): " |
| << *ISE << '\n'); |
| IVUses.pop_back(); |
| return false; |
| } |
| } |
| LLVM_DEBUG(if (SE->getSCEV(I) != ISE) dbgs() |
| << " NORMALIZED TO: " << *ISE << '\n'); |
| } |
| } |
| return true; |
| } |
| |
| IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) { |
| IVUses.push_back(new IVStrideUse(this, User, Operand)); |
| return IVUses.back(); |
| } |
| |
| IVUsers::IVUsers(Loop *L, AssumptionCache *AC, LoopInfo *LI, DominatorTree *DT, |
| ScalarEvolution *SE) |
| : L(L), AC(AC), LI(LI), DT(DT), SE(SE), IVUses() { |
| // Collect ephemeral values so that AddUsersIfInteresting skips them. |
| EphValues.clear(); |
| CodeMetrics::collectEphemeralValues(L, AC, EphValues); |
| |
| // Find all uses of induction variables in this loop, and categorize |
| // them by stride. Start by finding all of the PHI nodes in the header for |
| // this loop. If they are induction variables, inspect their uses. |
| for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) |
| (void)AddUsersIfInteresting(&*I); |
| } |
| |
| void IVUsers::print(raw_ostream &OS, const Module *M) const { |
| OS << "IV Users for loop "; |
| L->getHeader()->printAsOperand(OS, false); |
| if (SE->hasLoopInvariantBackedgeTakenCount(L)) { |
| OS << " with backedge-taken count " << *SE->getBackedgeTakenCount(L); |
| } |
| OS << ":\n"; |
| |
| for (const IVStrideUse &IVUse : IVUses) { |
| OS << " "; |
| IVUse.getOperandValToReplace()->printAsOperand(OS, false); |
| OS << " = " << *getReplacementExpr(IVUse); |
| for (auto PostIncLoop : IVUse.PostIncLoops) { |
| OS << " (post-inc with loop "; |
| PostIncLoop->getHeader()->printAsOperand(OS, false); |
| OS << ")"; |
| } |
| OS << " in "; |
| if (IVUse.getUser()) |
| IVUse.getUser()->print(OS); |
| else |
| OS << "Printing <null> User"; |
| OS << '\n'; |
| } |
| } |
| |
| #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) |
| LLVM_DUMP_METHOD void IVUsers::dump() const { print(dbgs()); } |
| #endif |
| |
| void IVUsers::releaseMemory() { |
| Processed.clear(); |
| IVUses.clear(); |
| } |
| |
| IVUsersWrapperPass::IVUsersWrapperPass() : LoopPass(ID) { |
| initializeIVUsersWrapperPassPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| void IVUsersWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<AssumptionCacheTracker>(); |
| AU.addRequired<LoopInfoWrapperPass>(); |
| AU.addRequired<DominatorTreeWrapperPass>(); |
| AU.addRequired<ScalarEvolutionWrapperPass>(); |
| AU.setPreservesAll(); |
| } |
| |
| bool IVUsersWrapperPass::runOnLoop(Loop *L, LPPassManager &LPM) { |
| auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache( |
| *L->getHeader()->getParent()); |
| auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); |
| auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); |
| auto *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE(); |
| |
| IU.reset(new IVUsers(L, AC, LI, DT, SE)); |
| return false; |
| } |
| |
| void IVUsersWrapperPass::print(raw_ostream &OS, const Module *M) const { |
| IU->print(OS, M); |
| } |
| |
| void IVUsersWrapperPass::releaseMemory() { IU->releaseMemory(); } |
| |
| /// getReplacementExpr - Return a SCEV expression which computes the |
| /// value of the OperandValToReplace. |
| const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const { |
| return SE->getSCEV(IU.getOperandValToReplace()); |
| } |
| |
| /// getExpr - Return the expression for the use. |
| const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const { |
| return normalizeForPostIncUse(getReplacementExpr(IU), IU.getPostIncLoops(), |
| *SE); |
| } |
| |
| static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) { |
| if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) { |
| if (AR->getLoop() == L) |
| return AR; |
| return findAddRecForLoop(AR->getStart(), L); |
| } |
| |
| if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { |
| for (const auto *Op : Add->operands()) |
| if (const SCEVAddRecExpr *AR = findAddRecForLoop(Op, L)) |
| return AR; |
| return nullptr; |
| } |
| |
| return nullptr; |
| } |
| |
| const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const { |
| if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L)) |
| return AR->getStepRecurrence(*SE); |
| return nullptr; |
| } |
| |
| void IVStrideUse::transformToPostInc(const Loop *L) { |
| PostIncLoops.insert(L); |
| } |
| |
| void IVStrideUse::deleted() { |
| // Remove this user from the list. |
| Parent->Processed.erase(this->getUser()); |
| Parent->IVUses.erase(this); |
| // this now dangles! |
| } |