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[SCEV] Use nw flag and symbolic iteration count to sharpen ranges of AddRecs

Authored by mkazantsev on Thu, Oct 15, 10:00 PM.

Description

[SCEV] Use nw flag and symbolic iteration count to sharpen ranges of AddRecs

We can sharpen the range of a AddRec if we know that it does not
self-wrap and know the symbolic iteration count in the loop. If we can
evaluate the value of AddRec on the last iteration and prove that at least
one its intermediate value lies between start and end, then no-wrap flag
allows us to conclude that all of them also lie between start and end. So
the estimate of range can be improved to union of ranges of start and end.

Differential Revision: https://reviews.llvm.org/D89381
Reviewed By: efriedma