[PATCH] D71717: [MachineScheduler] Ignore artificial edges when forming store chains

[Stanislav Mekhanoshin via Phabricator via llvm-commits]

rampitec added a comment.

In D71717#1792285 <https://reviews.llvm.org/D71717#1792285>, @foad wrote:

> > Maybe logic of artificial edges creation needs to be revised instead?
>
> Maybe. I don't really understand this logic. If it is not required for correctness, maybe it should add Weak edges instead of Artificial edges?


AFAIR the logic is to cross-transfer all successors to all successors to prevent any of them to be scheduled inside the cluster. The same for predecessors to prevent any predecessor to be scheduled inside the cluster. But that way we end up with a forest of cross edges.

Also any user transformation may insert artificial edges for any other reason. I do not think we can simple ignore them without removing them.

Maybe what we need instead of cross edges is to have a single post-dominator node which will become a singe predecessor for all successors of the nodes in a cluster. The same is for predecessors, we could just use a single dominator to be a common successor of predecessors. I.e. to have just two guard nodes instead of all of them being guards. I think a first and a last node in a cluster could become such single use guards.


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