[Bug fortran/106268] New: [suboptimal] Remove unnecessary loops releated to fortran compare to ifort

[Bug fortran/106268] New: [suboptimal] Remove unnecessary loops releated to fortran compare to ifort

[zhongyunde at huawei dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106268

            Bug ID: 106268
           Summary: [suboptimal] Remove unnecessary loops releated to
                    fortran compare to ifort
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zhongyunde at huawei dot com
  Target Milestone: ---

For the kernel inner loop body, gcc generate an loop, while icc doesn't, see
detail in https://godbolt.org/z/G77nKnf8W.
```
    DO i = 1, 10000
      do l = 1, ADM_lall
        rhogw_vm(:,ADM_kmin  ,l) = 0.D0
        rhogw_vm(:,ADM_kmax+1,l) = 0.D0
      enddo
    enddo
```

[Bug fortran/106268] [suboptimal] Remove unnecessary loops releated to fortran compare to ifort

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106268

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |missed-optimization
   Last reconfirmed|                            |2022-07-12
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think ICC elides the outer loop, it does keep the inner loop where GCC
unrolls the inner loop, keeping the outer loop.  There's no "benchmark loop"
elimination in GCC yet, instead we rely on code sinking which, at the moment,
cannot sink the memset calls out of the outer loop.

#include <string.h>
void foo (int *mem, int n)
{
  for (int i = 0; i < 1000; ++i)
    memset (mem, 0, n * sizeof (int));
}

ICC probably manages to elide the loop around the memset here.

[Bug tree-optimization/106268] [suboptimal] Remove unnecessary loops releated to fortran compare to ifort

[zhongyunde at huawei dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106268

--- Comment #2 from vfdff <zhongyunde at huawei dot com> ---
it seems different for the C version, see detail
https://godbolt.org/z/vc1edYKhf

in your above case, the icc also doesn't elide the outer loop.