//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "indvars"
-
#include "llvm/Transforms/Utils/SimplifyIndVar.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
-#include "llvm/Analysis/IVUsers.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.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(NumElimCmp , "Number of IV comparisons eliminated");
namespace {
- /// SimplifyIndvar - This is a utility for simplifying induction variables
+ /// 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.
Loop *L;
LoopInfo *LI;
ScalarEvolution *SE;
- const DataLayout *DL; // May be NULL
+ DominatorTree *DT;
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),
- DeadInsts(Dead),
- Changed(false) {
- DataLayoutPass *DLP = LPM->getAnalysisIfAvailable<DataLayoutPass>();
- DL = DLP ? &DLP->getDataLayout() : 0;
+ SimplifyIndvar(Loop *Loop, ScalarEvolution *SE, DominatorTree *DT,
+ LoopInfo *LI,SmallVectorImpl<WeakVH> &Dead)
+ : L(Loop), LI(LI), SE(SE), DT(DT), DeadInsts(Dead), Changed(false) {
assert(LI && "IV simplification requires LoopInfo");
}
/// 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);
+ /// 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 eliminateIVUser(Instruction *UseInst, Instruction *IVOperand);
void eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand);
void eliminateIVRemainder(BinaryOperator *Rem, Value *IVOperand,
bool IsSigned);
+ bool strengthenOverflowingOperation(BinaryOperator *OBO, Value *IVOperand);
Instruction *splitOverflowIntrinsic(Instruction *IVUser,
const DominatorTree *DT);
};
}
-/// foldIVUser - Fold an IV operand into its use. This removes increments of an
+/// 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.
/// be folded (in case more folding opportunities have been exposed).
/// Otherwise return null.
Value *SimplifyIndvar::foldIVUser(Instruction *UseInst, Instruction *IVOperand) {
- Value *IVSrc = 0;
+ Value *IVSrc = nullptr;
unsigned OperIdx = 0;
- const SCEV *FoldedExpr = 0;
+ const SCEV *FoldedExpr = nullptr;
switch (UseInst->getOpcode()) {
default:
- return 0;
+ 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 0;
+ 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 0;
+ return nullptr;
IVSrc = IVOperand->getOperand(0);
// IVSrc must be the (SCEVable) IV, since the other operand is const.
// Get a constant for the divisor. See createSCEV.
uint32_t BitWidth = cast<IntegerType>(UseInst->getType())->getBitWidth();
if (D->getValue().uge(BitWidth))
- return 0;
+ return nullptr;
D = ConstantInt::get(UseInst->getContext(),
APInt::getOneBitSet(BitWidth, D->getZExtValue()));
}
// We have something that might fold it's operand. Compare SCEVs.
if (!SE->isSCEVable(UseInst->getType()))
- return 0;
+ return nullptr;
// Bypass the operand if SCEV can prove it has no effect.
if (SE->getSCEV(UseInst) != FoldedExpr)
- return 0;
+ return nullptr;
DEBUG(dbgs() << "INDVARS: Eliminated IV operand: " << *IVOperand
<< " -> " << *UseInst << '\n');
++NumElimOperand;
Changed = true;
if (IVOperand->use_empty())
- DeadInsts.push_back(IVOperand);
+ DeadInsts.emplace_back(IVOperand);
return IVSrc;
}
-/// eliminateIVComparison - SimplifyIVUsers helper for eliminating useless
+/// SimplifyIVUsers helper for eliminating useless
/// comparisons against an induction variable.
void SimplifyIndvar::eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) {
unsigned IVOperIdx = 0;
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))
+ if (SE->isKnownPredicate(Pred, S, X)) {
ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext()));
- else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X))
+ 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()));
- else
+ DeadInsts.emplace_back(ICmp);
+ DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
+ } else if (isa<PHINode>(IVOperand) &&
+ SE->isLoopInvariantPredicate(Pred, S, X, ICmpLoop,
+ 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));
+
+ for (Value *Incoming : cast<PHINode>(IVOperand)->incoming_values()) {
+ if (NewLHS && NewRHS)
+ break;
+
+ 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;
- DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
++NumElimCmp;
Changed = true;
- DeadInsts.push_back(ICmp);
}
-/// eliminateIVRemainder - SimplifyIVUsers helper for eliminating useless
+/// SimplifyIVUsers helper for eliminating useless
/// remainder operations operating on an induction variable.
void SimplifyIndvar::eliminateIVRemainder(BinaryOperator *Rem,
Value *IVOperand,
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));
+ const SCEV *LessOne = SE->getMinusSCEV(S, SE->getOne(S->getType()));
if (IsSigned && !SE->isKnownNonNegative(LessOne))
return;
DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
++NumElimRem;
Changed = true;
- DeadInsts.push_back(Rem);
+ DeadInsts.emplace_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.
+/// 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)) {
}
}
- // Eliminate any operation that SCEV can prove is an identity function.
+ 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.push_back(UseInst);
+ 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);
+
+ 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);
+ 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);
+ if (ExtendAfterOp == OpAfterExtend) {
+ BO->setHasNoSignedWrap();
+ SE->forgetValue(BO);
+ Changed = true;
+ }
+ }
+
+ return Changed;
+}
+
/// \brief Split sadd.with.overflow into add + sadd.with.overflow to allow
/// analysis and optimization.
///
return IVUser;
// Find a branch guarded by the overflow check.
- BranchInst *Branch = 0;
- Instruction *AddVal = 0;
+ BranchInst *Branch = nullptr;
+ Instruction *AddVal = nullptr;
for (User *U : II->users()) {
if (ExtractValueInst *ExtractInst = dyn_cast<ExtractValueInst>(U)) {
if (ExtractInst->getNumIndices() != 1)
"Bad add instruction created from overflow intrinsic.");
AddVal->replaceAllUsesWith(AddInst);
- DeadInsts.push_back(AddVal);
+ DeadInsts.emplace_back(AddVal);
return AddInst;
}
-/// pushIVUsers - Add all uses of Def to the current IV's worklist.
-///
+/// Add all uses of Def to the current IV's worklist.
static void pushIVUsers(
Instruction *Def,
SmallPtrSet<Instruction*,16> &Simplified,
// 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))
+ if (UI != Def && Simplified.insert(UI).second)
SimpleIVUsers.push_back(std::make_pair(UI, Def));
}
}
-/// isSimpleIVUser - Return true if this instruction generates a simple SCEV
+/// 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
return false;
}
-/// simplifyUsers - Iteratively perform simplification on a worklist of users
+/// 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.
+/// 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.
///
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);
void IVVisitor::anchor() { }
-/// simplifyUsersOfIV - Simplify instructions that use this induction variable
+/// 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);
+bool simplifyUsersOfIV(PHINode *CurrIV, ScalarEvolution *SE, DominatorTree *DT,
+ LoopInfo *LI, SmallVectorImpl<WeakVH> &Dead,
+ IVVisitor *V) {
+ SimplifyIndvar SIV(LI->getLoopFor(CurrIV->getParent()), SE, DT, LI, Dead);
SIV.simplifyUsers(CurrIV, V);
return SIV.hasChanged();
}
-/// simplifyLoopIVs - Simplify users of induction variables within this
+/// 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 simplifyLoopIVs(Loop *L, ScalarEvolution *SE, DominatorTree *DT,
+ LoopInfo *LI, 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);
+ Changed |= simplifyUsersOfIV(cast<PHINode>(I), SE, DT, LI, Dead);
}
return Changed;
}
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