[PATCH] Fix bug 22641

[Sanjoy Das]

> I think the most obvious bug here is my implicit assumption that the step is positive. So we're looking at a post-increment recurrence and calling it PreAR. Maybe we should have a comment about that?

I'm not sure if I understand you -- what does the sign (or
non-zeroness) of step have to do with this transform?  From
AR={S+X,+,X} we constructed PreAR={S,+,X} so isn't PreAR the
pre-increment recurrence for AR irrespective of the sign of X?

-- Sanjoy