[Bug c/116016] enhancement: add __builtin_set_counted_by(P->FAM, COUNT) or equivalent

[isanbard at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116016

--- Comment #21 from Bill Wendling <isanbard at gmail dot com> ---
Another question: Should we allow side-effects in the builtin? I think it would
cause too much pain if we did. If we don't allow it, should it emit a warning
or silently become a no-op?