Hi Thomas,

Following your off-line explanation that the seemingly empty looking
assembly line forces an effective reload from memory, all is now clear.

OK for mainline and for backporting as you see fit.

Thanks for the patch.

Paul


On Sat, 7 Jan 2023 at 15:46, Thomas Koenig via Fortran <fortran@gcc.gnu.org>
wrote:

> Hello world,
>
> this patch fixes Fortran's handling of common subexpression elimination
> across ieee_set_rouding_mode calls.  It does so using a rather big
> hammer, by issuing a memory barrier to force reload from memory
> (and thus a recomputation).
>
> This is a rather big hammer, so if there are more elegant ways
> to fix it, I am very much open to suggestions.
>
> If PR 34678 is fixed, then this solution can also be applied here.
>
> OK for trunk?  How do you feel about a backport?
>
> Best regards
>
>         Thomas
>
> Add memory barrier for calls to ieee_set_rounding_mode.
>
> gcc/fortran/ChangeLog:
>
>          PR fortran/108329
>          * trans-expr.cc (trans_memory_barrier): New functions.
>          (gfc_conv_procedure_call): Insert memory barrier for
>          ieee_set_rounding_mode.
>
> gcc/testsuite/ChangeLog:
>
>          PR fortran/108329
>          * gfortran.dg/rounding_4.f90: New test.



-- 
"If you can't explain it simply, you don't understand it well enough" -
Albert Einstein