[Bug fortran/94841] [10 Regression]527.cam4_r 7.68% regression on Intel Cascadelaker with -O2, 9.57% regression with -Ofast -march=native -funroll-loops -flto

[tkoenig at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94841

Thomas Koenig <tkoenig at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=94788,
                   |                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=93956,
                   |                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=93114
             Status|WAITING                     |RESOLVED

--- Comment #2 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #1)
> Probably the mentioned inefficiency but the fix was a correctness one.

I had to revert the patch because fixing one correctness issue introduced
another one (PR 94788).

> Needs a testcase, fortran folks do not have access to SPEC and the question
> is whether the inefficiency can be fixed for the problematical case(s).

In this particular case, the cause of the inefficiency is clear - creating
a temporary because it is not kown if a pointer returned from a
procedure has a span or not. And if we don't know, we need to do something
about that, such as creating a temporary.

We need to revisit this whole thing for gcc 11, also for PR 93114.

I have some ideas already.  Marking this as fixed in the meantime.