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[IRCE] Fix how IRCE checks for no-sign-overflow.

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IRCE requires the induction variables it handles to not sign-overflow.
The current scheme of checking if sext({X,+,S}) == {sext(X),+,sext(S)}
fails when SCEV simplifies sext(X) too.  After this change we //also//
check no-signed-wrap by looking at the flags set on the SCEVAddRecExpr.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233102 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjoy Das 2015-03-24 19:29:22 +00:00
parent 33a864aae2
commit fe1187ead7
1 changed files with 26 additions and 16 deletions
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42
lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
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@ -707,30 +707,40 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE, BranchProbabilityInfo &BP
}
}
auto IsInductionVar = [&SE](const SCEVAddRecExpr *AR, bool &IsIncreasing) {
if (!AR->isAffine())
return false;
auto HasNoSignedWrap = [&](const SCEVAddRecExpr *AR) {
if (AR->getNoWrapFlags(SCEV::FlagNSW))
return true;
IntegerType *Ty = cast<IntegerType>(AR->getType());
IntegerType *WideTy =
IntegerType::get(Ty->getContext(), Ty->getBitWidth() * 2);
const SCEVAddRecExpr *ExtendAfterOp =
dyn_cast<SCEVAddRecExpr>(SE.getSignExtendExpr(AR, WideTy));
if (ExtendAfterOp) {
const SCEV *ExtendedStart = SE.getSignExtendExpr(AR->getStart(), WideTy);
const SCEV *ExtendedStep =
SE.getSignExtendExpr(AR->getStepRecurrence(SE), WideTy);
bool NoSignedWrap = ExtendAfterOp->getStart() == ExtendedStart &&
ExtendAfterOp->getStepRecurrence(SE) == ExtendedStep;
if (NoSignedWrap)
return true;
}
// We may have proved this when computing the sign extension above.
return AR->getNoWrapFlags(SCEV::FlagNSW) != SCEV::FlagAnyWrap;
};
auto IsInductionVar = [&](const SCEVAddRecExpr *AR, bool &IsIncreasing) {
if (!AR->isAffine())
return false;
// Currently we only work with induction variables that have been proved to
// not wrap. This restriction can potentially be lifted in the future.
const SCEVAddRecExpr *ExtendAfterOp =
dyn_cast<SCEVAddRecExpr>(SE.getSignExtendExpr(AR, WideTy));
if (!ExtendAfterOp)
return false;
const SCEV *ExtendedStart = SE.getSignExtendExpr(AR->getStart(), WideTy);
const SCEV *ExtendedStep =
SE.getSignExtendExpr(AR->getStepRecurrence(SE), WideTy);
bool NoSignedWrap = ExtendAfterOp->getStart() == ExtendedStart &&
ExtendAfterOp->getStepRecurrence(SE) == ExtendedStep;
if (!NoSignedWrap)
if (!HasNoSignedWrap(AR))
return false;
if (const SCEVConstant *StepExpr =