[Bug target/92566] New: rs6000_preferred_simd_mode isn't very good

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92566

            Bug ID: 92566
           Summary: rs6000_preferred_simd_mode isn't very good
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: segher at gcc dot gnu.org
  Target Milestone: ---

As mentioned in PR92557, at least we shouldn't return V2DImode for the
vector mode for DImode, if we do not actually support that.