[Bug rtl-optimization/64081] [5/6/7 Regression] r217827 prevents RTL loop unroll

["law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64081

--- Comment #55 from Jeffrey A. Law <law at redhat dot com> ---
And presumably other calls to get_simple_loop_desc need the more permissive
definition to re-enable loop unrolling.  Ugh.

I think at the least we're going to have to look at each caller of
get_simple_loop_desc and decide if that use is safe with the more permissive
definition.

Hopefully the important one for loop unrolling is safe and we can then look at
how to untangle things a bit.  Perhaps with a boolean indicating if the strict
or permissive definition is needed, or perhaps by storing into the returned
descriptor which definition was used, then the callers decide what to do with
that information, or something along those lines.