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Diffstat (limited to 'contrib/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp | 722 |
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diff --git a/contrib/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/contrib/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp new file mode 100644 index 000000000000..faa14046b1e3 --- /dev/null +++ b/contrib/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp @@ -0,0 +1,722 @@ +//===-- SimplifyIndVar.cpp - Induction variable simplification ------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements induction variable simplification. It does +// not define any actual pass or policy, but provides a single function to +// simplify a loop's induction variables based on ScalarEvolution. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Utils/SimplifyIndVar.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/ScalarEvolutionExpressions.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" + +using namespace llvm; + +#define DEBUG_TYPE "indvars" + +STATISTIC(NumElimIdentity, "Number of IV identities eliminated"); +STATISTIC(NumElimOperand, "Number of IV operands folded into a use"); +STATISTIC(NumElimRem , "Number of IV remainder operations eliminated"); +STATISTIC( + NumSimplifiedSDiv, + "Number of IV signed division operations converted to unsigned division"); +STATISTIC(NumElimCmp , "Number of IV comparisons eliminated"); + +namespace { + /// This is a utility for simplifying induction variables + /// based on ScalarEvolution. It is the primary instrument of the + /// IndvarSimplify pass, but it may also be directly invoked to cleanup after + /// other loop passes that preserve SCEV. + class SimplifyIndvar { + Loop *L; + LoopInfo *LI; + ScalarEvolution *SE; + DominatorTree *DT; + + SmallVectorImpl<WeakTrackingVH> &DeadInsts; + + bool Changed; + + public: + SimplifyIndvar(Loop *Loop, ScalarEvolution *SE, DominatorTree *DT, + LoopInfo *LI, SmallVectorImpl<WeakTrackingVH> &Dead) + : L(Loop), LI(LI), SE(SE), DT(DT), DeadInsts(Dead), Changed(false) { + assert(LI && "IV simplification requires LoopInfo"); + } + + bool hasChanged() const { return Changed; } + + /// Iteratively perform simplification on a worklist of users of the + /// specified induction variable. This is the top-level driver that applies + /// all simplifications to users of an IV. + void simplifyUsers(PHINode *CurrIV, IVVisitor *V = nullptr); + + Value *foldIVUser(Instruction *UseInst, Instruction *IVOperand); + + bool eliminateIdentitySCEV(Instruction *UseInst, Instruction *IVOperand); + + bool eliminateOverflowIntrinsic(CallInst *CI); + bool eliminateIVUser(Instruction *UseInst, Instruction *IVOperand); + void eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand); + void eliminateIVRemainder(BinaryOperator *Rem, Value *IVOperand, + bool IsSigned); + bool eliminateSDiv(BinaryOperator *SDiv); + bool strengthenOverflowingOperation(BinaryOperator *OBO, Value *IVOperand); + }; +} + +/// Fold an IV operand into its use. This removes increments of an +/// aligned IV when used by a instruction that ignores the low bits. +/// +/// IVOperand is guaranteed SCEVable, but UseInst may not be. +/// +/// Return the operand of IVOperand for this induction variable if IVOperand can +/// be folded (in case more folding opportunities have been exposed). +/// Otherwise return null. +Value *SimplifyIndvar::foldIVUser(Instruction *UseInst, Instruction *IVOperand) { + Value *IVSrc = nullptr; + unsigned OperIdx = 0; + const SCEV *FoldedExpr = nullptr; + switch (UseInst->getOpcode()) { + default: + return nullptr; + case Instruction::UDiv: + case Instruction::LShr: + // We're only interested in the case where we know something about + // the numerator and have a constant denominator. + if (IVOperand != UseInst->getOperand(OperIdx) || + !isa<ConstantInt>(UseInst->getOperand(1))) + return nullptr; + + // Attempt to fold a binary operator with constant operand. + // e.g. ((I + 1) >> 2) => I >> 2 + if (!isa<BinaryOperator>(IVOperand) + || !isa<ConstantInt>(IVOperand->getOperand(1))) + return nullptr; + + IVSrc = IVOperand->getOperand(0); + // IVSrc must be the (SCEVable) IV, since the other operand is const. + assert(SE->isSCEVable(IVSrc->getType()) && "Expect SCEVable IV operand"); + + ConstantInt *D = cast<ConstantInt>(UseInst->getOperand(1)); + if (UseInst->getOpcode() == Instruction::LShr) { + // Get a constant for the divisor. See createSCEV. + uint32_t BitWidth = cast<IntegerType>(UseInst->getType())->getBitWidth(); + if (D->getValue().uge(BitWidth)) + return nullptr; + + D = ConstantInt::get(UseInst->getContext(), + APInt::getOneBitSet(BitWidth, D->getZExtValue())); + } + FoldedExpr = SE->getUDivExpr(SE->getSCEV(IVSrc), SE->getSCEV(D)); + } + // We have something that might fold it's operand. Compare SCEVs. + if (!SE->isSCEVable(UseInst->getType())) + return nullptr; + + // Bypass the operand if SCEV can prove it has no effect. + if (SE->getSCEV(UseInst) != FoldedExpr) + return nullptr; + + DEBUG(dbgs() << "INDVARS: Eliminated IV operand: " << *IVOperand + << " -> " << *UseInst << '\n'); + + UseInst->setOperand(OperIdx, IVSrc); + assert(SE->getSCEV(UseInst) == FoldedExpr && "bad SCEV with folded oper"); + + ++NumElimOperand; + Changed = true; + if (IVOperand->use_empty()) + DeadInsts.emplace_back(IVOperand); + return IVSrc; +} + +/// SimplifyIVUsers helper for eliminating useless +/// comparisons against an induction variable. +void SimplifyIndvar::eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) { + unsigned IVOperIdx = 0; + ICmpInst::Predicate Pred = ICmp->getPredicate(); + if (IVOperand != ICmp->getOperand(0)) { + // Swapped + assert(IVOperand == ICmp->getOperand(1) && "Can't find IVOperand"); + IVOperIdx = 1; + Pred = ICmpInst::getSwappedPredicate(Pred); + } + + // Get the SCEVs for the ICmp operands. + const SCEV *S = SE->getSCEV(ICmp->getOperand(IVOperIdx)); + const SCEV *X = SE->getSCEV(ICmp->getOperand(1 - IVOperIdx)); + + // Simplify unnecessary loops away. + const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent()); + S = SE->getSCEVAtScope(S, ICmpLoop); + X = SE->getSCEVAtScope(X, ICmpLoop); + + ICmpInst::Predicate InvariantPredicate; + const SCEV *InvariantLHS, *InvariantRHS; + + // If the condition is always true or always false, replace it with + // a constant value. + if (SE->isKnownPredicate(Pred, S, X)) { + ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext())); + DeadInsts.emplace_back(ICmp); + DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n'); + } else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X)) { + ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext())); + DeadInsts.emplace_back(ICmp); + DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n'); + } else if (isa<PHINode>(IVOperand) && + SE->isLoopInvariantPredicate(Pred, S, X, L, InvariantPredicate, + InvariantLHS, InvariantRHS)) { + + // Rewrite the comparison to a loop invariant comparison if it can be done + // cheaply, where cheaply means "we don't need to emit any new + // instructions". + + Value *NewLHS = nullptr, *NewRHS = nullptr; + + if (S == InvariantLHS || X == InvariantLHS) + NewLHS = + ICmp->getOperand(S == InvariantLHS ? IVOperIdx : (1 - IVOperIdx)); + + if (S == InvariantRHS || X == InvariantRHS) + NewRHS = + ICmp->getOperand(S == InvariantRHS ? IVOperIdx : (1 - IVOperIdx)); + + auto *PN = cast<PHINode>(IVOperand); + for (unsigned i = 0, e = PN->getNumIncomingValues(); + i != e && (!NewLHS || !NewRHS); + ++i) { + + // If this is a value incoming from the backedge, then it cannot be a loop + // invariant value (since we know that IVOperand is an induction variable). + if (L->contains(PN->getIncomingBlock(i))) + continue; + + // NB! This following assert does not fundamentally have to be true, but + // it is true today given how SCEV analyzes induction variables. + // Specifically, today SCEV will *not* recognize %iv as an induction + // variable in the following case: + // + // define void @f(i32 %k) { + // entry: + // br i1 undef, label %r, label %l + // + // l: + // %k.inc.l = add i32 %k, 1 + // br label %loop + // + // r: + // %k.inc.r = add i32 %k, 1 + // br label %loop + // + // loop: + // %iv = phi i32 [ %k.inc.l, %l ], [ %k.inc.r, %r ], [ %iv.inc, %loop ] + // %iv.inc = add i32 %iv, 1 + // br label %loop + // } + // + // but if it starts to, at some point, then the assertion below will have + // to be changed to a runtime check. + + Value *Incoming = PN->getIncomingValue(i); + +#ifndef NDEBUG + if (auto *I = dyn_cast<Instruction>(Incoming)) + assert(DT->dominates(I, ICmp) && "Should be a unique loop dominating value!"); +#endif + + const SCEV *IncomingS = SE->getSCEV(Incoming); + + if (!NewLHS && IncomingS == InvariantLHS) + NewLHS = Incoming; + if (!NewRHS && IncomingS == InvariantRHS) + NewRHS = Incoming; + } + + if (!NewLHS || !NewRHS) + // We could not find an existing value to replace either LHS or RHS. + // Generating new instructions has subtler tradeoffs, so avoid doing that + // for now. + return; + + DEBUG(dbgs() << "INDVARS: Simplified comparison: " << *ICmp << '\n'); + ICmp->setPredicate(InvariantPredicate); + ICmp->setOperand(0, NewLHS); + ICmp->setOperand(1, NewRHS); + } else + return; + + ++NumElimCmp; + Changed = true; +} + +bool SimplifyIndvar::eliminateSDiv(BinaryOperator *SDiv) { + // Get the SCEVs for the ICmp operands. + auto *N = SE->getSCEV(SDiv->getOperand(0)); + auto *D = SE->getSCEV(SDiv->getOperand(1)); + + // Simplify unnecessary loops away. + const Loop *L = LI->getLoopFor(SDiv->getParent()); + N = SE->getSCEVAtScope(N, L); + D = SE->getSCEVAtScope(D, L); + + // Replace sdiv by udiv if both of the operands are non-negative + if (SE->isKnownNonNegative(N) && SE->isKnownNonNegative(D)) { + auto *UDiv = BinaryOperator::Create( + BinaryOperator::UDiv, SDiv->getOperand(0), SDiv->getOperand(1), + SDiv->getName() + ".udiv", SDiv); + UDiv->setIsExact(SDiv->isExact()); + SDiv->replaceAllUsesWith(UDiv); + DEBUG(dbgs() << "INDVARS: Simplified sdiv: " << *SDiv << '\n'); + ++NumSimplifiedSDiv; + Changed = true; + DeadInsts.push_back(SDiv); + return true; + } + + return false; +} + +/// SimplifyIVUsers helper for eliminating useless +/// remainder operations operating on an induction variable. +void SimplifyIndvar::eliminateIVRemainder(BinaryOperator *Rem, + Value *IVOperand, + bool IsSigned) { + // We're only interested in the case where we know something about + // the numerator. + if (IVOperand != Rem->getOperand(0)) + return; + + // Get the SCEVs for the ICmp operands. + const SCEV *S = SE->getSCEV(Rem->getOperand(0)); + const SCEV *X = SE->getSCEV(Rem->getOperand(1)); + + // Simplify unnecessary loops away. + const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent()); + S = SE->getSCEVAtScope(S, ICmpLoop); + X = SE->getSCEVAtScope(X, ICmpLoop); + + // i % n --> i if i is in [0,n). + if ((!IsSigned || SE->isKnownNonNegative(S)) && + SE->isKnownPredicate(IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, + S, X)) + Rem->replaceAllUsesWith(Rem->getOperand(0)); + else { + // (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n). + const SCEV *LessOne = SE->getMinusSCEV(S, SE->getOne(S->getType())); + if (IsSigned && !SE->isKnownNonNegative(LessOne)) + return; + + if (!SE->isKnownPredicate(IsSigned ? + ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, + LessOne, X)) + return; + + ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ, + Rem->getOperand(0), Rem->getOperand(1)); + SelectInst *Sel = + SelectInst::Create(ICmp, + ConstantInt::get(Rem->getType(), 0), + Rem->getOperand(0), "tmp", Rem); + Rem->replaceAllUsesWith(Sel); + } + + DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n'); + ++NumElimRem; + Changed = true; + DeadInsts.emplace_back(Rem); +} + +bool SimplifyIndvar::eliminateOverflowIntrinsic(CallInst *CI) { + auto *F = CI->getCalledFunction(); + if (!F) + return false; + + typedef const SCEV *(ScalarEvolution::*OperationFunctionTy)( + const SCEV *, const SCEV *, SCEV::NoWrapFlags, unsigned); + typedef const SCEV *(ScalarEvolution::*ExtensionFunctionTy)( + const SCEV *, Type *); + + OperationFunctionTy Operation; + ExtensionFunctionTy Extension; + + Instruction::BinaryOps RawOp; + + // We always have exactly one of nsw or nuw. If NoSignedOverflow is false, we + // have nuw. + bool NoSignedOverflow; + + switch (F->getIntrinsicID()) { + default: + return false; + + case Intrinsic::sadd_with_overflow: + Operation = &ScalarEvolution::getAddExpr; + Extension = &ScalarEvolution::getSignExtendExpr; + RawOp = Instruction::Add; + NoSignedOverflow = true; + break; + + case Intrinsic::uadd_with_overflow: + Operation = &ScalarEvolution::getAddExpr; + Extension = &ScalarEvolution::getZeroExtendExpr; + RawOp = Instruction::Add; + NoSignedOverflow = false; + break; + + case Intrinsic::ssub_with_overflow: + Operation = &ScalarEvolution::getMinusSCEV; + Extension = &ScalarEvolution::getSignExtendExpr; + RawOp = Instruction::Sub; + NoSignedOverflow = true; + break; + + case Intrinsic::usub_with_overflow: + Operation = &ScalarEvolution::getMinusSCEV; + Extension = &ScalarEvolution::getZeroExtendExpr; + RawOp = Instruction::Sub; + NoSignedOverflow = false; + break; + } + + const SCEV *LHS = SE->getSCEV(CI->getArgOperand(0)); + const SCEV *RHS = SE->getSCEV(CI->getArgOperand(1)); + + auto *NarrowTy = cast<IntegerType>(LHS->getType()); + auto *WideTy = + IntegerType::get(NarrowTy->getContext(), NarrowTy->getBitWidth() * 2); + + const SCEV *A = + (SE->*Extension)((SE->*Operation)(LHS, RHS, SCEV::FlagAnyWrap, 0u), + WideTy); + const SCEV *B = + (SE->*Operation)((SE->*Extension)(LHS, WideTy), + (SE->*Extension)(RHS, WideTy), SCEV::FlagAnyWrap, 0u); + + if (A != B) + return false; + + // Proved no overflow, nuke the overflow check and, if possible, the overflow + // intrinsic as well. + + BinaryOperator *NewResult = BinaryOperator::Create( + RawOp, CI->getArgOperand(0), CI->getArgOperand(1), "", CI); + + if (NoSignedOverflow) + NewResult->setHasNoSignedWrap(true); + else + NewResult->setHasNoUnsignedWrap(true); + + SmallVector<ExtractValueInst *, 4> ToDelete; + + for (auto *U : CI->users()) { + if (auto *EVI = dyn_cast<ExtractValueInst>(U)) { + if (EVI->getIndices()[0] == 1) + EVI->replaceAllUsesWith(ConstantInt::getFalse(CI->getContext())); + else { + assert(EVI->getIndices()[0] == 0 && "Only two possibilities!"); + EVI->replaceAllUsesWith(NewResult); + } + ToDelete.push_back(EVI); + } + } + + for (auto *EVI : ToDelete) + EVI->eraseFromParent(); + + if (CI->use_empty()) + CI->eraseFromParent(); + + return true; +} + +/// Eliminate an operation that consumes a simple IV and has no observable +/// side-effect given the range of IV values. IVOperand is guaranteed SCEVable, +/// but UseInst may not be. +bool SimplifyIndvar::eliminateIVUser(Instruction *UseInst, + Instruction *IVOperand) { + if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) { + eliminateIVComparison(ICmp, IVOperand); + return true; + } + if (BinaryOperator *Bin = dyn_cast<BinaryOperator>(UseInst)) { + bool IsSRem = Bin->getOpcode() == Instruction::SRem; + if (IsSRem || Bin->getOpcode() == Instruction::URem) { + eliminateIVRemainder(Bin, IVOperand, IsSRem); + return true; + } + + if (Bin->getOpcode() == Instruction::SDiv) + return eliminateSDiv(Bin); + } + + if (auto *CI = dyn_cast<CallInst>(UseInst)) + if (eliminateOverflowIntrinsic(CI)) + return true; + + if (eliminateIdentitySCEV(UseInst, IVOperand)) + return true; + + return false; +} + +/// Eliminate any operation that SCEV can prove is an identity function. +bool SimplifyIndvar::eliminateIdentitySCEV(Instruction *UseInst, + Instruction *IVOperand) { + if (!SE->isSCEVable(UseInst->getType()) || + (UseInst->getType() != IVOperand->getType()) || + (SE->getSCEV(UseInst) != SE->getSCEV(IVOperand))) + return false; + + // getSCEV(X) == getSCEV(Y) does not guarantee that X and Y are related in the + // dominator tree, even if X is an operand to Y. For instance, in + // + // %iv = phi i32 {0,+,1} + // br %cond, label %left, label %merge + // + // left: + // %X = add i32 %iv, 0 + // br label %merge + // + // merge: + // %M = phi (%X, %iv) + // + // getSCEV(%M) == getSCEV(%X) == {0,+,1}, but %X does not dominate %M, and + // %M.replaceAllUsesWith(%X) would be incorrect. + + if (isa<PHINode>(UseInst)) + // If UseInst is not a PHI node then we know that IVOperand dominates + // UseInst directly from the legality of SSA. + if (!DT || !DT->dominates(IVOperand, UseInst)) + return false; + + if (!LI->replacementPreservesLCSSAForm(UseInst, IVOperand)) + return false; + + DEBUG(dbgs() << "INDVARS: Eliminated identity: " << *UseInst << '\n'); + + UseInst->replaceAllUsesWith(IVOperand); + ++NumElimIdentity; + Changed = true; + DeadInsts.emplace_back(UseInst); + return true; +} + +/// Annotate BO with nsw / nuw if it provably does not signed-overflow / +/// unsigned-overflow. Returns true if anything changed, false otherwise. +bool SimplifyIndvar::strengthenOverflowingOperation(BinaryOperator *BO, + Value *IVOperand) { + + // Fastpath: we don't have any work to do if `BO` is `nuw` and `nsw`. + if (BO->hasNoUnsignedWrap() && BO->hasNoSignedWrap()) + return false; + + const SCEV *(ScalarEvolution::*GetExprForBO)(const SCEV *, const SCEV *, + SCEV::NoWrapFlags, unsigned); + switch (BO->getOpcode()) { + default: + return false; + + case Instruction::Add: + GetExprForBO = &ScalarEvolution::getAddExpr; + break; + + case Instruction::Sub: + GetExprForBO = &ScalarEvolution::getMinusSCEV; + break; + + case Instruction::Mul: + GetExprForBO = &ScalarEvolution::getMulExpr; + break; + } + + unsigned BitWidth = cast<IntegerType>(BO->getType())->getBitWidth(); + Type *WideTy = IntegerType::get(BO->getContext(), BitWidth * 2); + const SCEV *LHS = SE->getSCEV(BO->getOperand(0)); + const SCEV *RHS = SE->getSCEV(BO->getOperand(1)); + + bool Changed = false; + + if (!BO->hasNoUnsignedWrap()) { + const SCEV *ExtendAfterOp = SE->getZeroExtendExpr(SE->getSCEV(BO), WideTy); + const SCEV *OpAfterExtend = (SE->*GetExprForBO)( + SE->getZeroExtendExpr(LHS, WideTy), SE->getZeroExtendExpr(RHS, WideTy), + SCEV::FlagAnyWrap, 0u); + if (ExtendAfterOp == OpAfterExtend) { + BO->setHasNoUnsignedWrap(); + SE->forgetValue(BO); + Changed = true; + } + } + + if (!BO->hasNoSignedWrap()) { + const SCEV *ExtendAfterOp = SE->getSignExtendExpr(SE->getSCEV(BO), WideTy); + const SCEV *OpAfterExtend = (SE->*GetExprForBO)( + SE->getSignExtendExpr(LHS, WideTy), SE->getSignExtendExpr(RHS, WideTy), + SCEV::FlagAnyWrap, 0u); + if (ExtendAfterOp == OpAfterExtend) { + BO->setHasNoSignedWrap(); + SE->forgetValue(BO); + Changed = true; + } + } + + return Changed; +} + +/// Add all uses of Def to the current IV's worklist. +static void pushIVUsers( + Instruction *Def, + SmallPtrSet<Instruction*,16> &Simplified, + SmallVectorImpl< std::pair<Instruction*,Instruction*> > &SimpleIVUsers) { + + for (User *U : Def->users()) { + Instruction *UI = cast<Instruction>(U); + + // Avoid infinite or exponential worklist processing. + // Also ensure unique worklist users. + // If Def is a LoopPhi, it may not be in the Simplified set, so check for + // self edges first. + if (UI != Def && Simplified.insert(UI).second) + SimpleIVUsers.push_back(std::make_pair(UI, Def)); + } +} + +/// Return true if this instruction generates a simple SCEV +/// expression in terms of that IV. +/// +/// This is similar to IVUsers' isInteresting() but processes each instruction +/// non-recursively when the operand is already known to be a simpleIVUser. +/// +static bool isSimpleIVUser(Instruction *I, const Loop *L, ScalarEvolution *SE) { + if (!SE->isSCEVable(I->getType())) + return false; + + // Get the symbolic expression for this instruction. + const SCEV *S = SE->getSCEV(I); + + // Only consider affine recurrences. + const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S); + if (AR && AR->getLoop() == L) + return true; + + return false; +} + +/// Iteratively perform simplification on a worklist of users +/// of the specified induction variable. Each successive simplification may push +/// more users which may themselves be candidates for simplification. +/// +/// This algorithm does not require IVUsers analysis. Instead, it simplifies +/// instructions in-place during analysis. Rather than rewriting induction +/// variables bottom-up from their users, it transforms a chain of IVUsers +/// top-down, updating the IR only when it encounters a clear optimization +/// opportunity. +/// +/// Once DisableIVRewrite is default, LSR will be the only client of IVUsers. +/// +void SimplifyIndvar::simplifyUsers(PHINode *CurrIV, IVVisitor *V) { + if (!SE->isSCEVable(CurrIV->getType())) + return; + + // Instructions processed by SimplifyIndvar for CurrIV. + SmallPtrSet<Instruction*,16> Simplified; + + // Use-def pairs if IV users waiting to be processed for CurrIV. + SmallVector<std::pair<Instruction*, Instruction*>, 8> SimpleIVUsers; + + // Push users of the current LoopPhi. In rare cases, pushIVUsers may be + // called multiple times for the same LoopPhi. This is the proper thing to + // do for loop header phis that use each other. + pushIVUsers(CurrIV, Simplified, SimpleIVUsers); + + while (!SimpleIVUsers.empty()) { + std::pair<Instruction*, Instruction*> UseOper = + SimpleIVUsers.pop_back_val(); + Instruction *UseInst = UseOper.first; + + // Bypass back edges to avoid extra work. + if (UseInst == CurrIV) continue; + + Instruction *IVOperand = UseOper.second; + for (unsigned N = 0; IVOperand; ++N) { + assert(N <= Simplified.size() && "runaway iteration"); + + Value *NewOper = foldIVUser(UseOper.first, IVOperand); + if (!NewOper) + break; // done folding + IVOperand = dyn_cast<Instruction>(NewOper); + } + if (!IVOperand) + continue; + + if (eliminateIVUser(UseOper.first, IVOperand)) { + pushIVUsers(IVOperand, Simplified, SimpleIVUsers); + continue; + } + + if (BinaryOperator *BO = dyn_cast<BinaryOperator>(UseOper.first)) { + if (isa<OverflowingBinaryOperator>(BO) && + strengthenOverflowingOperation(BO, IVOperand)) { + // re-queue uses of the now modified binary operator and fall + // through to the checks that remain. + pushIVUsers(IVOperand, Simplified, SimpleIVUsers); + } + } + + CastInst *Cast = dyn_cast<CastInst>(UseOper.first); + if (V && Cast) { + V->visitCast(Cast); + continue; + } + if (isSimpleIVUser(UseOper.first, L, SE)) { + pushIVUsers(UseOper.first, Simplified, SimpleIVUsers); + } + } +} + +namespace llvm { + +void IVVisitor::anchor() { } + +/// Simplify instructions that use this induction variable +/// by using ScalarEvolution to analyze the IV's recurrence. +bool simplifyUsersOfIV(PHINode *CurrIV, ScalarEvolution *SE, DominatorTree *DT, + LoopInfo *LI, SmallVectorImpl<WeakTrackingVH> &Dead, + IVVisitor *V) { + SimplifyIndvar SIV(LI->getLoopFor(CurrIV->getParent()), SE, DT, LI, Dead); + SIV.simplifyUsers(CurrIV, V); + return SIV.hasChanged(); +} + +/// Simplify users of induction variables within this +/// loop. This does not actually change or add IVs. +bool simplifyLoopIVs(Loop *L, ScalarEvolution *SE, DominatorTree *DT, + LoopInfo *LI, SmallVectorImpl<WeakTrackingVH> &Dead) { + bool Changed = false; + for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) { + Changed |= simplifyUsersOfIV(cast<PHINode>(I), SE, DT, LI, Dead); + } + return Changed; +} + +} // namespace llvm |