[PATCH] D84220: [IPSCCP] Fix a bug that the "returned" attribute is not cleared when function is optimized to return undef

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

The current definition of "returned" in LangRef is unclear, yes.

In terms of what we actually want, the "must be equal or else instant UB" variation seems more useful than the "must be equal or poison" variation.  With "must be equal or poison", basically the only legal optimization is replacing the result with the argument. The only reason I can think of we wouldn't want the instant UB is if it interacts badly with some significant number of optimizations.  I'm not coming up with anything it could interact badly with off the top of my head, though, and any transform that did have an issue would also interact badly with noundef.


Repository:
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  https://reviews.llvm.org/D84220/new/

https://reviews.llvm.org/D84220