[Bug target/96933] rs6000: inefficient code for char/short vec CTOR

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96933

--- Comment #9 from Segher Boessenkool <segher at gcc dot gnu.org> ---
I'm not sure what you mean.

vmrglb merges the vectors
  abcdefghijklmnop
and
  ABCDEFGHIJKLMNOP
to
  iIjJkKlLmMnNoOpP

... ah, I see what you mean I guess.

So, use something else instead?  How about vpku*um?

First vpkudum, xforming
  xxxxxxxAxxxxxxxB
and
  xxxxxxxCxxxxxxxD
into
  xxxAxxxBxxxCxxxD

and then vpkuwum:
  xxxAxxxBxxxCxxxD
and
  xxxExxxFxxxGxxxH
into
  xAxBxCxDxExFxGxH

and finally vpkuhum:
  xAxBxCxDxExFxGxH
and
  xIxJxKxLxMxNxOxP
into
  ABCDEFGHIJKLMNOP

?