[PATCH] D81806: [DivergenceAnalysis] mark join of divergent loop exits

[Sameer Sahasrabuddhe via Phabricator via llvm-commits]

sameerds added a comment.

In D81806#2094869 <https://reviews.llvm.org/D81806#2094869>, @simoll wrote:

> I am a bit surprised this is necessary. Actually, join divergence in `bb3` should come about as a result of `propagateLoopDivergence` for the `[bb1, bb2]` loop and not immediately because it is a divergent exit.


I am not sure what you mean here. propagateLoopDivergence is calling propagateJoinDivergence ... so doesn't that count as a result of the former?

> Also, a divergent loop exit does not automatically become join divergent, eg:
> 
>   bb1: 
>      %m.uni = <uni>
>      %n.uni = <uni>
>      br <uni>, %bb2, %bb3
>    
>   bb2: [..]
>      br <div>, %bb2, %bb3
>    
>   bb3:
>      %x.uni = phi [%m.uni, %bb2], [%n.uni %bb1]  <-- divergent loop exit that is not join divergent

But here, bb3 is not a join block for the bb2 loop, since there is only one path from the loop exit reaching bb3.


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