[PATCH] D93734: [LoopDeletion] Insert an early exit from dead path in loop
Jonas Paulsson via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Dec 22 16:18:16 PST 2020
jonpa added a comment.
In D93734#2469137 <https://reviews.llvm.org/D93734#2469137>, @jdoerfert wrote:
> The idea is that we have
>
> H:
> %c = ... ; invariant wrt H and L
> br %c, L, B
> B:
> side_effects
> br L
> L:
> br %x, H, Exit
>
> Exit:
> ...
>
> right?
Yes, exactly (could be more blocks than 3, though, of course).
> One of my problems is that this is too tied to the syntax.
How do you mean, exactly?
> Another is that we are not deleting a loop. The former can be addressed later I guess.
>
> Isn't this more related to LoopUnswitch?
> We want to "unswitch the paths that are side-effect free", or something like that.
I thought that if we cannot delete the whole loop we can effectively delete a part of it with an early exit.
LoopUnswitching only works if the condition is loop invariant currently as far as I can see, so I am not sure how simple that would be...
> We could also make it generic by collecting the blocks that are allowed on such a path
> in order to allow different CFGs. But that can be done later as well.
Might be worth a try...
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