[PATCH] D147954: [SimplifyCFG] Merge branch_weights for direct callsites and introduce options to preserve value profile for indirect callsites

[Wenlei He via Phabricator via llvm-commits]

wenlei added a comment.

Just to make sure I understand it correctly. The solution to the issue Teresa raised,

>> In other cases (non-LTO and instrumentation PGO) ICP appears to be performed right after profile annotation.
>
> However, we also perform SimplifyCFG at least once before profile annotation (both sample and instrumentation PGO). Wouldn't we still end up merging indirect calls in some cases too aggressively, because they don't have any profile metadata so we won't know any better? I'm currently testing a change to avoid speculation in SimplifyCFG before profile annotation to avoid doing incorrectly aggressive transformations. We might want to do something similar here too: setPreserveIndirectCallInstWithProfInHoistAndSink(false) for all pre-PGO annotation invocations of SimplifyCFG in PGO compiles.

is to not rely on pre-link vs post-link to decide when to enable/disable hoist/sink for calls, but to check whether calls have target value profile remaining (i.e. ICP yet to happen) so we can always avoid destroying profile for ICP regardless of where simpilifyCFG is run. Is that correct?


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https://reviews.llvm.org/D147954