[Bug target/81593] Optimize PowerPC vector set from vector extract

[meissner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81593

--- Comment #1 from Michael Meissner <meissner at gcc dot gnu.org> ---
Created attachment 41852
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41852&action=edit
Proposed patch to fix the problem

Checked on power7 big endian and power8 little endian.