Re: [PATCH] c-family: implement -ffp-contract=on

[Richard Biener <richard.guenther@gmail.com>]

On Mon, May 22, 2023 at 5:16 PM Alexander Monakov <amonakov@ispras.ru> wrote:
>
>
> On Mon, 22 May 2023, Richard Biener wrote:
>
> > On Thu, May 18, 2023 at 11:04 PM Alexander Monakov via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> > >
> > > Implement -ffp-contract=on for C and C++ without changing default
> > > behavior (=off for -std=cNN, =fast for C++ and -std=gnuNN).
> >
> > The documentation changes mention the defaults are changed for
> > standard modes, I suppose you want to remove that hunk.
>
> No, the current documentation is incomplete, and that hunk extends it
> to match the current GCC behavior. Should I break it out to a separate
> patch? I see this drive-by fix could look confusing — sorry about that.
>
> > it would be possible to do
> >
> >   *expr_p = build_call_expr_internal (ifn, type, ops[0], ops[1]. ops[2]);
> >   return GS_OK;
> >
> > and not worry about temporary creation and gimplifying of the operands.
> > That would in theory also leave the possibility to do this during
> > genericization instead (and avoid the guard against late invocation of
> > the hook).
>
> Ah, no, I deliberately decided against that, because that way we would go
> via gimplify_arg, which would emit all side effects in *pre_p. That seems
> wrong if arguments had side-effects that should go in *post_p.

Ah, true - that warrants a comment though.

Richard.

>
> Thanks.
> Alexander
>
> > Otherwise it looks OK, but I'll let frontend maintainers have a chance to look
> > as well.
> >
> > Thanks for tackling this long-standing issue.
> > Richard.