[Bug target/89271] [9 Regression] gcc.target/powerpc/vsx-simode2.c stopped working in GCC 9

[amodra at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89271

--- Comment #5 from Alan Modra <amodra at gmail dot com> ---
Created attachment 45760
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=45760&action=edit
Current set of patches

It turns out there is a lot more than just wrong register_move_cost.  This
patchset does fix the PR without introducing too many regressions, but it is a
work in progress.

I have some questions about union register classes:
1) What should register_move_cost return for a union class like GEN_OR_VSX_REGS
and some other class?  Worst case, best case, or doesn't it matter?
2) What should preferred_reload_class return for union classes?
Looking at other ports doesn't shed much light..