[PATCH] D106852: [SCEV] Fix getAddExpr for adding loop invariants into start of some AddRec

[Serguei Katkov via Phabricator via llvm-commits]

skatkov added a comment.

In D106852#2907747 <https://reviews.llvm.org/D106852#2907747>, @efriedma wrote:

> When you're checking for is0thIterationGuaranteed, do you also need to check for abnormal exits from the loop?

This is a good question. If I understand your question correctly you are asking about abnormal exit in outer loop,
before entering the current loop. Probably it is a problem.

> What happens if you just assume is0thIterationGuaranteed is always false?  I'm not sure all this work to try to prove the flags is worth doing.

At least no-one LLVM test is failing. Do you propose to just always say that we cannot guarantee 0th iteration?
I'll update the patch. If it will cause any performance issue we can return to discussion how to detect that 0th iteration is possible.


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