//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "indvars"
-
-#include "llvm/Instructions.h"
-#include "llvm/Analysis/Dominators.h"
+#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"
+#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/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;
+#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.
class SimplifyIndvar {
Loop *L;
LoopInfo *LI;
- DominatorTree *DT;
ScalarEvolution *SE;
- const TargetData *TD; // May be NULL
+ const DataLayout *DL; // May be NULL
SmallVectorImpl<WeakVH> &DeadInsts;
public:
SimplifyIndvar(Loop *Loop, ScalarEvolution *SE, LPPassManager *LPM,
- SmallVectorImpl<WeakVH> &Dead, IVUsers *IVU = NULL) :
+ SmallVectorImpl<WeakVH> &Dead, IVUsers *IVU = nullptr) :
L(Loop),
LI(LPM->getAnalysisIfAvailable<LoopInfo>()),
SE(SE),
- TD(LPM->getAnalysisIfAvailable<TargetData>()),
DeadInsts(Dead),
Changed(false) {
+ DataLayoutPass *DLP = LPM->getAnalysisIfAvailable<DataLayoutPass>();
+ DL = DLP ? &DLP->getDataLayout() : nullptr;
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);
+ void simplifyUsers(PHINode *CurrIV, IVVisitor *V = nullptr);
Value *foldIVUser(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(BitWidth, 1).shl(D->getZExtValue()));
+ 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 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');
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;
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,
DeadInsts.push_back(Rem);
}
-/// eliminateIVUser - Eliminate an operation that consumes a simple IV and has
+/// 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,
return true;
}
-/// pushIVUsers - Add all uses of Def to the current IV's worklist.
+/// 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) {
+
+ // Currently we only handle instructions of the form "add <indvar> <value>"
+ // and "sub <indvar> <value>".
+ unsigned Op = BO->getOpcode();
+ if (!(Op == Instruction::Add || Op == Instruction::Sub))
+ return false;
+
+ // If BO is already both nuw and nsw then there is nothing left to do
+ if (BO->hasNoUnsignedWrap() && BO->hasNoSignedWrap())
+ return false;
+
+ IntegerType *IT = cast<IntegerType>(IVOperand->getType());
+ Value *OtherOperand = nullptr;
+ int OtherOperandIdx = -1;
+ if (BO->getOperand(0) == IVOperand) {
+ OtherOperand = BO->getOperand(1);
+ OtherOperandIdx = 1;
+ } else {
+ assert(BO->getOperand(1) == IVOperand && "only other use!");
+ OtherOperand = BO->getOperand(0);
+ OtherOperandIdx = 0;
+ }
+
+ bool Changed = false;
+ const SCEV *OtherOpSCEV = SE->getSCEV(OtherOperand);
+ if (OtherOpSCEV == SE->getCouldNotCompute())
+ return false;
+
+ if (Op == Instruction::Sub) {
+ // If the subtraction is of the form "sub <indvar>, <op>", then pretend it
+ // is "add <indvar>, -<op>" and continue, else bail out.
+ if (OtherOperandIdx != 1)
+ return false;
+
+ OtherOpSCEV = SE->getNegativeSCEV(OtherOpSCEV);
+ }
+
+ const SCEV *IVOpSCEV = SE->getSCEV(IVOperand);
+ const SCEV *ZeroSCEV = SE->getConstant(IVOpSCEV->getType(), 0);
+
+ if (!BO->hasNoSignedWrap()) {
+ // Upgrade the add to an "add nsw" if we can prove that it will never
+ // sign-overflow or sign-underflow.
+
+ const SCEV *SignedMax =
+ SE->getConstant(APInt::getSignedMaxValue(IT->getBitWidth()));
+ const SCEV *SignedMin =
+ SE->getConstant(APInt::getSignedMinValue(IT->getBitWidth()));
+
+ // The addition "IVOperand + OtherOp" does not sign-overflow if the result
+ // is sign-representable in 2's complement in the given bit-width.
+ //
+ // If OtherOp is SLT 0, then for an IVOperand in [SignedMin - OtherOp,
+ // SignedMax], "IVOperand + OtherOp" is in [SignedMin, SignedMax + OtherOp].
+ // Everything in [SignedMin, SignedMax + OtherOp] is representable since
+ // SignedMax + OtherOp is at least -1.
+ //
+ // If OtherOp is SGE 0, then for an IVOperand in [SignedMin, SignedMax -
+ // OtherOp], "IVOperand + OtherOp" is in [SignedMin + OtherOp, SignedMax].
+ // Everything in [SignedMin + OtherOp, SignedMax] is representable since
+ // SignedMin + OtherOp is at most -1.
+ //
+ // It follows that for all values of IVOperand in [SignedMin - smin(0,
+ // OtherOp), SignedMax - smax(0, OtherOp)] the result of the add is
+ // representable (i.e. there is no sign-overflow).
+
+ const SCEV *UpperDelta = SE->getSMaxExpr(ZeroSCEV, OtherOpSCEV);
+ const SCEV *UpperLimit = SE->getMinusSCEV(SignedMax, UpperDelta);
+
+ bool NeverSignedOverflows =
+ SE->isKnownPredicate(ICmpInst::ICMP_SLE, IVOpSCEV, UpperLimit);
+
+ if (NeverSignedOverflows) {
+ const SCEV *LowerDelta = SE->getSMinExpr(ZeroSCEV, OtherOpSCEV);
+ const SCEV *LowerLimit = SE->getMinusSCEV(SignedMin, LowerDelta);
+
+ bool NeverSignedUnderflows =
+ SE->isKnownPredicate(ICmpInst::ICMP_SGE, IVOpSCEV, LowerLimit);
+ if (NeverSignedUnderflows) {
+ BO->setHasNoSignedWrap(true);
+ Changed = true;
+ }
+ }
+ }
+
+ if (!BO->hasNoUnsignedWrap()) {
+ // Upgrade the add computing "IVOperand + OtherOp" to an "add nuw" if we can
+ // prove that it will never unsigned-overflow (i.e. the result will always
+ // be representable in the given bit-width).
+ //
+ // "IVOperand + OtherOp" is unsigned-representable in 2's complement iff it
+ // does not produce a carry. "IVOperand + OtherOp" produces no carry iff
+ // IVOperand ULE (UnsignedMax - OtherOp).
+
+ const SCEV *UnsignedMax =
+ SE->getConstant(APInt::getMaxValue(IT->getBitWidth()));
+ const SCEV *UpperLimit = SE->getMinusSCEV(UnsignedMax, OtherOpSCEV);
+
+ bool NeverUnsignedOverflows =
+ SE->isKnownPredicate(ICmpInst::ICMP_ULE, IVOpSCEV, UpperLimit);
+
+ if (NeverUnsignedOverflows) {
+ BO->setHasNoUnsignedWrap(true);
+ Changed = true;
+ }
+ }
+
+ return Changed;
+}
+
+/// \brief Split sadd.with.overflow into add + sadd.with.overflow to allow
+/// analysis and optimization.
///
+/// \return A new value representing the non-overflowing add if possible,
+/// otherwise return the original value.
+Instruction *SimplifyIndvar::splitOverflowIntrinsic(Instruction *IVUser,
+ const DominatorTree *DT) {
+ IntrinsicInst *II = dyn_cast<IntrinsicInst>(IVUser);
+ if (!II || II->getIntrinsicID() != Intrinsic::sadd_with_overflow)
+ return IVUser;
+
+ // Find a branch guarded by the overflow check.
+ BranchInst *Branch = nullptr;
+ Instruction *AddVal = nullptr;
+ for (User *U : II->users()) {
+ if (ExtractValueInst *ExtractInst = dyn_cast<ExtractValueInst>(U)) {
+ if (ExtractInst->getNumIndices() != 1)
+ continue;
+ if (ExtractInst->getIndices()[0] == 0)
+ AddVal = ExtractInst;
+ else if (ExtractInst->getIndices()[0] == 1 && ExtractInst->hasOneUse())
+ Branch = dyn_cast<BranchInst>(ExtractInst->user_back());
+ }
+ }
+ if (!AddVal || !Branch)
+ return IVUser;
+
+ BasicBlock *ContinueBB = Branch->getSuccessor(1);
+ if (std::next(pred_begin(ContinueBB)) != pred_end(ContinueBB))
+ return IVUser;
+
+ // Check if all users of the add are provably NSW.
+ bool AllNSW = true;
+ for (Use &U : AddVal->uses()) {
+ if (Instruction *UseInst = dyn_cast<Instruction>(U.getUser())) {
+ BasicBlock *UseBB = UseInst->getParent();
+ if (PHINode *PHI = dyn_cast<PHINode>(UseInst))
+ UseBB = PHI->getIncomingBlock(U);
+ if (!DT->dominates(ContinueBB, UseBB)) {
+ AllNSW = false;
+ break;
+ }
+ }
+ }
+ if (!AllNSW)
+ return IVUser;
+
+ // Go for it...
+ IRBuilder<> Builder(IVUser);
+ Instruction *AddInst = dyn_cast<Instruction>(
+ Builder.CreateNSWAdd(II->getOperand(0), II->getOperand(1)));
+
+ // The caller expects the new add to have the same form as the intrinsic. The
+ // IV operand position must be the same.
+ assert((AddInst->getOpcode() == Instruction::Add &&
+ AddInst->getOperand(0) == II->getOperand(0)) &&
+ "Bad add instruction created from overflow intrinsic.");
+
+ AddVal->replaceAllUsesWith(AddInst);
+ DeadInsts.push_back(AddVal);
+ return AddInst;
+}
+
+/// 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);
+ 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 (User != Def && Simplified.insert(User))
- SimpleIVUsers.push_back(std::make_pair(User, Def));
+ 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.
///
while (!SimpleIVUsers.empty()) {
std::pair<Instruction*, Instruction*> UseOper =
SimpleIVUsers.pop_back_val();
+ Instruction *UseInst = UseOper.first;
+
// Bypass back edges to avoid extra work.
- if (UseOper.first == CurrIV) continue;
+ if (UseInst == CurrIV) continue;
+
+ if (V && V->shouldSplitOverflowInstrinsics()) {
+ UseInst = splitOverflowIntrinsic(UseInst, V->getDomTree());
+ if (!UseInst)
+ continue;
+ }
Instruction *IVOperand = UseOper.second;
for (unsigned N = 0; IVOperand; ++N) {
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)
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) {
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