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fix a corner case in delinearization 

handle special cases Step==1, Step==-1, GCD==1, and GCD==-1

llvm-svn: 201868
This commit is contained in:
Sebastian Pop 2014-02-21 18:15:15 +00:00
parent 29026d3e52
commit 64f12d5324
1 changed files with 15 additions and 24 deletions
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39
llvm/lib/Analysis/ScalarEvolution.cpp
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@ -7255,46 +7255,37 @@ SCEVAddRecExpr::delinearize(ScalarEvolution &SE,
DEBUG(dbgs() << "(delinearize: " << *this << "\n");
// Currently we fail to delinearize when the stride of this SCEV is 1. We
// could decide to not fail in this case: we could just return 1 for the size
// of the subscript, and this same SCEV for the access function.
if (Step == One) {
DEBUG(dbgs() << "failed to delinearize " << *this << "\n)\n");
return this;
}
// When the stride of this SCEV is 1, do not compute the GCD: the size of this
// subscript is 1, and this same SCEV for the access function.
const SCEV *Remainder = Zero;
const SCEV *GCD = One;
// Find the GCD and Remainder of the Start and Step coefficients of this SCEV.
const SCEV *Remainder = NULL;
const SCEV *GCD = SCEVGCD::findGCD(SE, Start, Step, &Remainder);
if (Step != One && !Step->isAllOnesValue())
GCD = SCEVGCD::findGCD(SE, Start, Step, &Remainder);
DEBUG(dbgs() << "GCD: " << *GCD << "\n");
DEBUG(dbgs() << "Remainder: " << *Remainder << "\n");
// Same remark as above: we currently fail the delinearization, although we
// can very well handle this special case.
if (GCD == One) {
DEBUG(dbgs() << "failed to delinearize " << *this << "\n)\n");
return this;
}
const SCEV *Quotient = Start;
if (GCD != One && !GCD->isAllOnesValue())
// As findGCD computed Remainder, GCD divides "Start - Remainder." The
// Quotient is then this SCEV without Remainder, scaled down by the GCD. The
// Quotient is what will be used in the next subscript delinearization.
Quotient = SCEVDivision::divide(SE, SE.getMinusSCEV(Start, Remainder), GCD);
// As findGCD computed Remainder, GCD divides "Start - Remainder." The
// Quotient is then this SCEV without Remainder, scaled down by the GCD. The
// Quotient is what will be used in the next subscript delinearization.
const SCEV *Quotient =
SCEVDivision::divide(SE, SE.getMinusSCEV(Start, Remainder), GCD);
DEBUG(dbgs() << "Quotient: " << *Quotient << "\n");
const SCEV *Rem;
const SCEV *Rem = Quotient;
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Quotient))
// Recursively call delinearize on the Quotient until there are no more
// multiples that can be recognized.
Rem = AR->delinearize(SE, Subscripts, Sizes);
else
Rem = Quotient;
// Scale up the canonical induction variable IV by whatever remains from the
// Step after division by the GCD: the GCD is the size of all the sub-array.
if (Step != GCD) {
if (Step != One && !Step->isAllOnesValue() && GCD != One &&
!GCD->isAllOnesValue() && Step != GCD) {
Step = SCEVDivision::divide(SE, Step, GCD);
IV = SE.getMulExpr(IV, Step);
}