[PATCH] D97495: [SimplifyCFG] avoid illegal phi with both poison and undef

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In D97495#2589631 <https://reviews.llvm.org/D97495#2589631>, @aqjune wrote:

> What about updating redirectValuesFromPredecessorsToPhi to lower conflicting poison to undef?
> We can maintain two sets of incoming BBs, say BBundef and BBpoison that have poison incoming values and undef incoming values.
> At the end of redirectValuesFromPredecessorsToPhi, if BBundef and BBpoison overlaps, there are operands that need to be updated.
> It will keep the transformation enabled.

Yes, we can do better on this, but I suspect it's rare to encounter both poison and undef (and gets more rare as we eliminate more and more undef from IR?).


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