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Fix memcheck interval ends for pointers with negative strides

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Summary:
The checking pointer grouping algorithm assumes that the
starts/ends of the pointers are well formed (start <= end).

The runtime memory checking algorithm also assumes this by doing:

 start0 < end1 && start1 < end0

to detect conflicts. This check only works if start0 <= end0 and
start1 <= end1.

This change correctly orders the interval ends by either checking
the stride (if it is constant) or by using min/max SCEV expressions.

Reviewers: anemet, rengolin

Subscribers: rengolin, llvm-commits

Differential Revision: http://reviews.llvm.org/D11149

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242400 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Silviu Baranga
2015-07-16 14:02:58 +00:00
parent 5649b37b0e
commit e4877f25bd
2 changed files with 107 additions and 2 deletions
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20
lib/Analysis/LoopAccessAnalysis.cpp
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@@ -127,9 +127,25 @@ void RuntimePointerChecking::insert(Loop *Lp, Value *Ptr, bool WritePtr,
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Sc);
assert(AR && "Invalid addrec expression");
const SCEV *Ex = SE->getBackedgeTakenCount(Lp);
const SCEV *ScStart = AR->getStart();
const SCEV *ScEnd = AR->evaluateAtIteration(Ex, *SE);
Pointers.emplace_back(Ptr, AR->getStart(), ScEnd, WritePtr, DepSetId, ASId,
Sc);
const SCEV *Step = AR->getStepRecurrence(*SE);
// For expressions with negative step, the upper bound is ScStart and the
// lower bound is ScEnd.
if (const SCEVConstant *CStep = dyn_cast<const SCEVConstant>(Step)) {
if (CStep->getValue()->isNegative())
std::swap(ScStart, ScEnd);
} else {
// Fallback case: the step is not constant, but the we can still
// get the upper and lower bounds of the interval by using min/max
// expressions.
ScStart = SE->getUMinExpr(ScStart, ScEnd);
ScEnd = SE->getUMaxExpr(AR->getStart(), ScEnd);
}
Pointers.emplace_back(Ptr, ScStart, ScEnd, WritePtr, DepSetId, ASId, Sc);
}
bool RuntimePointerChecking::needsChecking(