https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118297
--- Comment #6 from Tibor Győri <tiborgyri at gmail dot com> --- (In reply to Andrew Pinski from comment #5) > (In reply to Tibor Győri from comment #4) > > It might even be the case that the current cost model is correct, > > vectorization is indeed sometimes unprofitable. > > But in that case, the issue is how this is communicated to the user, the > > "unsupported outerloop form" message does not feel informative enough. I > > mean it is a trivial loop that will get completely unrolled, right? So in my > > mind that already counts as "supported", but GCC is telling me it is not. > > Well there are 2 different kinds of vectorizer, the SLP and loop based one, > you were looking at the loop one which is saying it is unsupported. That is all true, but I would prefer if the loop vectorizer identified itself in its messages in the optimization report. Eg. prefix the messages with "loop-vect:" or something. Plus, "unsupported" is quite vague. Unsupported how? If I am reading the opt report, it is to figure out how to change my code to help the compiler, so it would be nice if the compiler was more specific. To suggest something actionable, currently this "unsupported outerloop form" message is emitted when any of the three different conditions listed above are met. If each of those conditions were checked separately, they could be given different, more specific missed-optimization messages.
