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...is which. It didn't matter so much when you were simply proving or disproving dependence, but when you compute direction, it's suddenly crucial. The problem is the computation of direction from distance. The code says: if (distance->isZero()) S->Direction = Subscript::EQ; else if (isGT) S->Direction = Subscript::GT; else S->Direction = Subscript::LT; While it looks sensible, it's incorrect. Correct is if (distance->isZero()) S->Direction = Subscript::EQ; else if (isGT) S->Direction = Subscript::LT; // !! else S->Direction = Subscript::GT; // !!...

...much when you were simply proving or disproving > dependence, but when you compute direction, it's suddenly crucial. > > The problem is the computation of direction from distance. The code says: > > if (distance->isZero()) > S->Direction = Subscript::EQ; > else if (isGT) > S->Direction = Subscript::GT; > else > S->Direction = Subscript::LT; > > > While it looks sensible, it's incorrect. Correct is > > > if (distance->isZero()) > S->Direction = Subscript::EQ; > else if (isGT) > S->Direction = Subscript:...

Hi Hal, Preston! Sorry for the delay! Got busy with some offline work. I've worked on my previous code to calculate direction and distance vectors whenever possible (strong SIV, basically). I think the current code is much clearer and would like your opinions on it. I have attached the patch and also pushed to the github repo I mentioned [1]. Thanks! [1]

Gents, I spent some time reading over Sanjoy's patch for LoopDependenceAnalysis. Unfortunately, an early version of these notes escaped; this is the complete review. First off, I agree with his choice to implement the SIV tests. For scientific Fortran, the SIV (and the simpler ZIV) tests cover about 85% of the cases in practice. For C and C++, I expect the percentage will be much higher.