[Bug fortran/67170] PRE can't hoist out a readonly argument

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67170

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Ok to make the alias-oracle approach more "scalable" we'd need to cache the
fn spec parameter/result bits in the functions PARM/RESULT_DECLs
(thus in tree_decl_common where we have conveniently 24bits left to put
in EAF_* and ERF_* flags).

Now fnspec is a type attribute so I'm not sure we can catch all cases
in the attribute handler or if we need to process each function body
(gimplifying parameters sounds like a good place to me for example).

I still think the FE should simplify the MEs life by doing the copy trick
for all intent-in scalars though.