Is it possible to update the callee node summary after profile annotate (using information from inline instances which are not inlined in early inline)?
David On Mon, Oct 14, 2013 at 2:18 PM, Dehao Chen <de...@google.com> wrote: > On Mon, Oct 14, 2013 at 12:49 PM, Jan Hubicka <hubi...@ucw.cz> wrote: >>> Not for instrumented FDO (not as I know of). But for AutoFDO, this >>> could be a potential risk because some callee is marked unlikely >>> executed simply because they are inlined and eliminated in the O2 >>> binary. But in ipa-inline it will not get inlined because the edge is >>> not hot from cgraph_maybe_hot_edge_p (because callee is >>> UNLIKELY_EXECUTED), while the edge->count is actually hot. >> >> Can't you prevent setting calle to UNLIKELY_EXECUTED in these cases instead? >> It seems that having profile set incorrectly will lead to other problems >> later, too. >> We discussed similar problem with Teresa about the missing profiles for >> comdat, >> basically one should detect these cases as profile being lost and go with >> guessed >> profile. (I believe patch for that was posted, too, and so far it seems >> best approach >> to this issue) > > The current AutoFDO implementation will take all functions that do not > have have profile as normally executed, thus use guessed profile for > it. This is like using profile for truly hot functions, and using O2 > for other functions. This works fine. However, it leads to larger code > size (approximately 10%~20% larger than FDO). > > I'd like to introduce another mode for users who care about both > performance and code size, and can be sure that profile is > representative. In this mode, we will mark all functions without > sample as "unlikely executed". However, because AutoFDO use debug info > (of optimized code) to represent profile, it's possible that some hot > functions (say foo) are inlined and fully eliminated into another hot > function (say bar). So in the profile, bar is cold, and because the > profile for foo::bar is eliminated, bar will not be inlined into foo > before the profile annotation. However, after profile annotate, we can > infer from the bb count that foo->bar is hot, thus it should be > inlined in ipa-inline phase. However, because bar itself is marked > UNLIKELY_EXECUTED, it will not be inlined. > > One possible workaround would be that during rebuild_cgraph_edges, if > we find an edge's callee is unlikely executed, add the edge count to > the callee's count and recalculate callee's frequency. > > Dehao > >> >> Honza
