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+//===-- 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.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "indvars"
+
+#include "llvm/Instructions.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/IVUsers.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/SimplifyIndVar.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+
+using namespace llvm;
+
+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(NumElimCmp , "Number of IV comparisons eliminated");
+
+namespace {
+ /// SimplifyIndvar - 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;
+ DominatorTree *DT;
+ ScalarEvolution *SE;
+ IVUsers *IU; // NULL for DisableIVRewrite
+ const TargetData *TD; // May be NULL
+
+ SmallVectorImpl<WeakVH> &DeadInsts;
+
+ bool Changed;
+
+ public:
+ SimplifyIndvar(Loop *Loop, ScalarEvolution *SE, LPPassManager *LPM,
+ SmallVectorImpl<WeakVH> &Dead, IVUsers *IVU = NULL) :
+ L(Loop),
+ LI(LPM->getAnalysisIfAvailable<LoopInfo>()),
+ SE(SE),
+ IU(IVU),
+ TD(LPM->getAnalysisIfAvailable<TargetData>()),
+ 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 simplicitions to users of an IV.
+ void simplifyUsers(PHINode *CurrIV, IVVisitor *V = NULL);
+
+ Value *foldIVUser(Instruction *UseInst, Instruction *IVOperand);
+
+ bool eliminateIVUser(Instruction *UseInst, Instruction *IVOperand);
+ void eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand);
+ void eliminateIVRemainder(BinaryOperator *Rem, Value *IVOperand,
+ bool IsSigned);
+ };
+}
+
+/// foldIVUser - 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 = 0;
+ unsigned OperIdx = 0;
+ const SCEV *FoldedExpr = 0;
+ switch (UseInst->getOpcode()) {
+ default:
+ return 0;
+ 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 0;
+
+ // Attempt to fold a binary operator with constant operand.
+ // e.g. ((I + 1) >> 2) => I >> 2
+ if (IVOperand->getNumOperands() != 2 ||
+ !isa<ConstantInt>(IVOperand->getOperand(1)))
+ return 0;
+
+ 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 0;
+
+ D = ConstantInt::get(UseInst->getContext(),
+ APInt(BitWidth, 1).shl(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 0;
+
+ // Bypass the operand if SCEV can prove it has no effect.
+ if (SE->getSCEV(UseInst) != FoldedExpr)
+ return 0;
+
+ 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.push_back(IVOperand);
+ return IVSrc;
+}
+
+/// eliminateIVComparison - 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);
+
+ // 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()));
+ else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X))
+ ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext()));
+ else
+ return;
+
+ DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
+ ++NumElimCmp;
+ Changed = true;
+ DeadInsts.push_back(ICmp);
+}
+
+/// eliminateIVRemainder - 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->getConstant(S->getType(), 1));
+ 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);
+ }
+
+ // Inform IVUsers about the new users.
+ if (IU) {
+ if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0)))
+ IU->AddUsersIfInteresting(I);
+ }
+ DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
+ ++NumElimRem;
+ Changed = true;
+ DeadInsts.push_back(Rem);
+}
+
+/// eliminateIVUser - 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 *Rem = dyn_cast<BinaryOperator>(UseInst)) {
+ bool IsSigned = Rem->getOpcode() == Instruction::SRem;
+ if (IsSigned || Rem->getOpcode() == Instruction::URem) {
+ eliminateIVRemainder(Rem, IVOperand, IsSigned);
+ return true;
+ }
+ }
+
+ // Eliminate any operation that SCEV can prove is an identity function.
+ if (!SE->isSCEVable(UseInst->getType()) ||
+ (UseInst->getType() != IVOperand->getType()) ||
+ (SE->getSCEV(UseInst) != SE->getSCEV(IVOperand)))
+ return false;
+
+ DEBUG(dbgs() << "INDVARS: Eliminated identity: " << *UseInst << '\n');
+
+ UseInst->replaceAllUsesWith(IVOperand);
+ ++NumElimIdentity;
+ Changed = true;
+ DeadInsts.push_back(UseInst);
+ return true;
+}
+
+/// pushIVUsers - 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 (Value::use_iterator UI = Def->use_begin(), E = Def->use_end();
+ UI != E; ++UI) {
+ Instruction *User = cast<Instruction>(*UI);
+
+ // 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 (User != Def && Simplified.insert(User))
+ SimpleIVUsers.push_back(std::make_pair(User, Def));
+ }
+}
+
+/// isSimpleIVUser - 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;
+}
+
+/// simplifyUsers - 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 encouters a clear optimization
+/// opportunitiy.
+///
+/// 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();
+ // Bypass back edges to avoid extra work.
+ if (UseOper.first == 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;
+ }
+ 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 {
+
+/// simplifyUsersOfIV - Simplify instructions that use this induction variable
+/// by using ScalarEvolution to analyze the IV's recurrence.
+bool simplifyUsersOfIV(PHINode *CurrIV, ScalarEvolution *SE, LPPassManager *LPM,
+ SmallVectorImpl<WeakVH> &Dead, IVVisitor *V)
+{
+ LoopInfo *LI = &LPM->getAnalysis<LoopInfo>();
+ SimplifyIndvar SIV(LI->getLoopFor(CurrIV->getParent()), SE, LPM, Dead);
+ SIV.simplifyUsers(CurrIV, V);
+ return SIV.hasChanged();
+}
+
+/// simplifyLoopIVs - Simplify users of induction variables within this
+/// loop. This does not actually change or add IVs.
+bool simplifyLoopIVs(Loop *L, ScalarEvolution *SE, LPPassManager *LPM,
+ SmallVectorImpl<WeakVH> &Dead) {
+ bool Changed = false;
+ for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
+ Changed |= simplifyUsersOfIV(cast<PHINode>(I), SE, LPM, Dead);
+ }
+ return Changed;
+}
+
+/// simplifyIVUsers - Perform simplification on instructions recorded by the
+/// IVUsers pass.
+///
+/// This is the old approach to IV simplification to be replaced by
+/// SimplifyLoopIVs.
+bool simplifyIVUsers(IVUsers *IU, ScalarEvolution *SE, LPPassManager *LPM,
+ SmallVectorImpl<WeakVH> &Dead) {
+ SimplifyIndvar SIV(IU->getLoop(), SE, LPM, Dead);
+
+ // Each round of simplification involves a round of eliminating operations
+ // followed by a round of widening IVs. A single IVUsers worklist is used
+ // across all rounds. The inner loop advances the user. If widening exposes
+ // more uses, then another pass through the outer loop is triggered.
+ for (IVUsers::iterator I = IU->begin(); I != IU->end(); ++I) {
+ Instruction *UseInst = I->getUser();
+ Value *IVOperand = I->getOperandValToReplace();
+
+ if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) {
+ SIV.eliminateIVComparison(ICmp, IVOperand);
+ continue;
+ }
+ if (BinaryOperator *Rem = dyn_cast<BinaryOperator>(UseInst)) {
+ bool IsSigned = Rem->getOpcode() == Instruction::SRem;
+ if (IsSigned || Rem->getOpcode() == Instruction::URem) {
+ SIV.eliminateIVRemainder(Rem, IVOperand, IsSigned);
+ continue;
+ }
+ }
+ }
+ return SIV.hasChanged();
+}
+
+} // namespace llvm
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