[PATCH] D69591: Devirtualize a call on alloca without waiting for post inline cleanup and next DevirtSCCRepeatedPass iteration.

[Hiroshi Yamauchi via Phabricator via llvm-commits]

yamauchi added a comment.

An old mailing list thread about a related issue: http://lists.llvm.org/pipermail/llvm-dev/2017-December/thread.html#119598. I checked that this patch also fixes the example cited there: https://godbolt.org/z/BP0jGT

An alternative idea from there is "to pass the value handles to the inliner through CGSCCUpdateResult and let the inliner augment it as the caller gets indirect calls due to inlining."
I think that would work. We can add to the list of indirect calls as we inline and find indirect calls (where this patch calls tryPromoteCall()) and then DevirtSCCRepeatedPass would check if any of the indirect call has become direct after the iteration. This would be a more general and yet precise approach to these cases.

Another from there is to repeat DevirtSCCRepeatedPass until a fix point. I think that would fix these cases, but as the DevirtSCCRepeatedPass termination is based on a heuristic (described above) and currently likely not repeated to a fix point, it may have other broader impact like potentially inlining a lot more, and increasing compile time. To detect a fix point, we'd need some way to communicate that sort of like the above CGSCCUpdateResult approach.


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