[PATCH] D58560: [AST] Set 'MayAlias' instead of 'MustAlias' in AliasSets for PHI nodes (bugzilla bug#36801)

[Alina Sbirlea via Phabricator via llvm-commits]

asbirlea added a comment.

>   Sure, if the PHI node is inside the loop, we're not optimizing it anyway, but I would expect it isn't uncommon to have a PHI node outside the loop, which this would block optimizing

I'm sorry, I don't really understand what you mean here. What blocked optimizations are you referring to?

> And I'm worried the SSAUpdater usage of ValueIsRAUWd could cause bugs elsewhere.

I agree. Both fixes proposed only address this known bug. There may be other bugs caused by this usage.
I'm not familiar enough with that piece of code to understand other potential bugs, but I think it is reasonable to try to address this issue soon since its a known miscompile.
That code in the SSAUpdater seems to not have changed for 7 years, so if that usage causes other bugs, they're very well hidden...


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