> On Aug 22, 2021, Jan Hubicka <hubi...@ucw.cz> wrote: > > > OK, thanks for looking into this issue! > > Thanks, I've finally installed it in the trunk. > > > It seems that analye_stmt indeed does not skip debug stmts. It is very > > odd we got so far without hitting build difference. > > Indeed. That got me thinking... The comments state: > > If the statement cannot be analyzed (for any reason), the entire > function cannot be analyzed by modref. > > but the implementation also tests, for every statement: > > || ((!summary || !summary->useful_p (ecf_flags, false)) > && (!summary_lto > || !summary_lto->useful_p (ecf_flags, false)))) > > which means that, if the first stmt of a block doesn't add useful > information to the summary, we give up. Was this really the intent? It is just early exit condition in case we already found enough side effects to give up on any useful info about loads/stores. Summaries are computed from optimistic one (function has no side effects) by becoming more pesimistic as statements are being visited.
So in most cases useful_p is true at the begining of the loop (since we see now loads/stores). I suppose we was hitting the difference because in const functions the summaries can be !useful_p from begining of the loop. I guess it is harmless to process the first statement in that case (if we do not produce debug bootstrap difference) Honza > > -- > Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/ > Free Software Activist GNU Toolchain Engineer > Disinformation flourishes because many people care deeply about injustice > but very few check the facts. Ask me about <https://stallmansupport.org>
