Re: Fix recursion discovery in ipa-pure-const

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

On Thu, Nov 11, 2021 at 2:41 PM Jan Hubicka via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi,
> We make self recursive functions as looping of fear of endless recursion.
> This is done correctly for local pure/const and for non-trivial SCCs in
> callgraph, but for trivial SCCs we miss the flag.
>
> I think it is bad decision since infinite recursion will run out of stack,

Note it might not always in case we can eliminate the tail-recursion or avoid
stack use by the recursion by other means.  So I think it is conservatively
correct.

Richard.

> but changing it upsets some testcases and should be done independently.
> So this patch is fixing current behaviour to be consistent.
>
> Bootstrapped/regtested x86_64-linux, comitted.
>
> gcc/ChangeLog:
>
> 2021-11-11  Jan Hubicka  <hubicka@ucw.cz>
>
>         * ipa-pure-const.c (propagate_pure_const): Self recursion is
>         a side effects.
>
> diff --git a/gcc/ipa-pure-const.c b/gcc/ipa-pure-const.c
> index 505ed4f8a3b..64777cd2d91 100644
> --- a/gcc/ipa-pure-const.c
> +++ b/gcc/ipa-pure-const.c
> @@ -1513,6 +1611,9 @@ propagate_pure_const (void)
>               enum pure_const_state_e edge_state = IPA_CONST;
>               bool edge_looping = false;
>
> +             if (e->recursive_p ())
> +               looping = true;
> +
>               if (dump_file && (dump_flags & TDF_DETAILS))
>                 {
>                   fprintf (dump_file, "    Call to %s",