[PATCH] c++: Add std::to_underlying to the set of stdlib functions that are always folded

[Ville Voutilainen]

On Tue, 13 May 2025 at 23:34, Jason Merrill <jason@redhat.com> wrote:
>
> On 5/13/25 4:29 PM, Ville Voutilainen wrote:
> > On Tue, 13 May 2025 at 23:23, Jason Merrill <jason@redhat.com> wrote:
> >>>            /* Check that the return and argument types are sane before
> >>>               folding.  */
> >>> -         if (INDIRECT_TYPE_P (TREE_TYPE (x))
> >>> -             && INDIRECT_TYPE_P (TREE_TYPE (r)))
> >>> +         if (id_equal (DECL_NAME (callee), "to_underlying")
> >>> +             || (INDIRECT_TYPE_P (TREE_TYPE (x))
> >>> +                 && INDIRECT_TYPE_P (TREE_TYPE (r))))
> >>
> >> Maybe instead of INDIRECT_TYPE_P, check ! AGGREGATE_TYPE_P ?  I'm not
> >> sure how much sanity checking we need here, maybe we should just trust
> >> the library.
> >
> > I.. ..don't think AGGREGATE_TYPE_P is right?
>
> I was suggesting *not* AGGREGATE_TYPE_P, because build_nop doesn't work
> for such types.

Ah, yes, got it. I did spot the 'not' but was wondering whether that
covers all the right cases, but for references and enumerators, I
guess
it would.

> > It seems to me that this
> > sanity check is checking that it's a cast between
> > references for the other ones, and that's just unsuitable for
> > to_underlying. I would suggest just removing that sanity
> > check and trusting the library.
>
> That's fine too.

I'll test the attached.
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