[Bug target/84280] [6/7/8 Regression] Performance regression in g++-7 with Eigen for non-AVX2 CPUs

["marxin at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84280

--- Comment #18 from Martin Liška <marxin at gcc dot gnu.org> ---
(In reply to Patrik Huber from comment #14)
> It even seems a few percent slower after the FDO stuff. But the `
> -fprofile-use` is a bit weird. If there is no .gcda file, it doesn't
> complain. If you give it a file that doesn't exist (e.g. -fprofile-use=foo),
> then it doesn't complain either. So how can I check whether it really ran
> the FDO?

Yep, maybe having an option that will cause failure would be a good idea.
Anyway, you can use -fdump-ipa-profile and check *.065i.profile file where you
should see something like:

...
Read edge from 0 to 2, count:1
1 edge counts read
...

Note that -fprofile-use=foo tells the compiler to search in *folder* foo for
corresponding gcda files.