[PATCH] D101291: [IndVars] avoid crash in LFTR when assuming an add recurrence

[Philip Reames via Phabricator via llvm-commits]

reames added a comment.

This patch looks suspiciously like it's fixing a symptom not the cause.  The test case in this review does not reproduce for me.  However, the original reduced case from the mentioned bug does.

Glancing at the SCEV for the original test before the transform shows that both the phi and the add *are* AddRecExprs.  I'd suggest printing the SCEVs at the point of crash to see what might have changed or to better understand how we can match a loop counter - which the example does appear to be - and yet end up with the increment not being an addrec.

Your patch seems like a workaround.  I suspect we'll see other problems if the expected pre-conditions to the LFTR method are not met.

To be clear, I'm not opposing a workaround if this is breaking something badly, I just want to make sure we don't stop at the workaround if there's a deeper issue here.


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https://reviews.llvm.org/D101291