[PATCH] D106331: [WIP][ScalarEvolution] Try harder to prove overflow in howManyLessThans.

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

The easiest thing here would be if SCEV recorded the flags somewhere... but unfortunately, we don't; when we discover the flags aren't universally applicable, we throw them away.  We could try to construct some sort of side-table, I guess, to provide an API `getNoWrapFlagsWithContext(SCEV*, Instruction*)`.  So basically the same logic as this, but factored away.

One alternative I considered is looking at the nowrap flags of the AddRec "IV - Stride".  We do often manage to deduce nsw/nuw, and if the backedge is taken, it proves Start - Stride doesn't overflow.  But if we're doing that, I'm not sure how we prove the case where the backedge isn't taken.


Repository:
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https://reviews.llvm.org/D106331