[PATCH] D29916: [CGP] Split some critical edges coming out of indirect branches

[Michael Kuperstein via Phabricator via llvm-commits]

mkuper added a comment.

In https://reviews.llvm.org/D29916#675732, @efriedma wrote:

> Would it be possible to split the edges in some less fragile manner?  I mean, in general you can "split" the edge from an indirectbr to a block with exactly one indirectbr predecessor by splitting the other predecessors.


I agree this is fragile in the sense that we need to hit a very specific pattern. But I don't have significantly better ideas.
I could try to generalize this, but I think we'd basically need to run both backward data-flow from the IBRs to make sure they're only fed by addresses from GVs (and at most one GV each), and forward data-flow from the GVs to make sure they aren't potentially written to. I'm not sure this is worth the trouble.

I don't really understand what you mean regarding splitting the other predecessors. I want to avoid having a phi on a block where one of the predecessor blocks on the phi is an indirectbr. I don't see how doing anything to the other incoming edges would help, you'll still end  with this phi, just change the other predecessors. (The reason this matters only when the edge is critical is because if the indirectbr has only one successor, it doesn't matter where the defs end up living.)

Regardless, I'd like to also extend this to split cases where we have several indirectbr predecessors (of this form).


https://reviews.llvm.org/D29916