[Bug target/79202] On Power8, consider using vupkhsw/xxpermdi to sign extend an int in a vector register instead of mfvsrwz/mtvsrwa

[meissner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79202

--- Comment #4 from Michael Meissner <meissner at gcc dot gnu.org> ---
Created attachment 40609
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40609&action=edit
Proposed patch to fix the problem.

This patch is believed to fix the following PRs
  * target/79038 (__float128/integer conversions)
  * target/79202 (consider using vupkhsw/xxpermdi to sign extend an int)
  * target/79203 (rework fp conversions to know about -mvsx-small-integer)