On Fri, Mar 10, 2023 at 06:54:10PM +0100, Thomas Koenig via Gcc-patches wrote:
> Hello world, here's the patch that was discussed.
>
> Regression-tested. OK for trunk?
>
> Since this appeared only in gcc13, I see no need for a backport.
> I will also document this in the changes file.
>
> Best regards
>
> Thomas
>
> Set -frapv if -std=legacy is set.
s/frapv/fwrapv/
> Fortran legacy codes sometimes contain linear congruential
> seudorandom number generators. These generators implicitly depend
> on wrapping behavior on integer overflow, which is illegal Fortran,
> but the best they could to at the time.
>
> A gcc13 change exposed this in rnflow, part of the Polyhedron
> benchmark, with -O3. Rather than "regress" on such code, this patch
> enables -fwrapv if -std=legacy is enabled. This allows the benchmark
> to run successfully, and presumably lots of other code as well.
I think it certainly shouldn't overwrite it, it can adjust the default,
but if user asks for -std=legacy -fno-wrapv or
-fno-wrapv -std=legacy, it should honor that.
> gcc/fortran/ChangeLog:
>
> PR fortran/109075
> * options.cc (gfc_handle_option): If -std=legacy is set,
s/ / /
> also set -frwapv.
s/rwapv/wrapv/
> * invoke.texi: Document the change.
> --- a/gcc/fortran/options.cc
> +++ b/gcc/fortran/options.cc
> @@ -797,6 +797,8 @@ gfc_handle_option (size_t scode, const char *arg,
> HOST_WIDE_INT value,
> case OPT_std_legacy:
> set_default_std_flags ();
> gfc_option.warn_std = 0;
> + /* -std=legacy implies -fwapv, but the user can override it. */
> + flag_wrapv = 1;
> break;
>
> case OPT_fshort_enums:
So, I think it should be done later, after option processing, say
in gfc_post_options if it is possible to determine if -std=legacy
has been specified (and not say -std=legacy -std=f2018 etc.),
and using SET_OPTION_IF_UNSET.
Jakub
