[Power9] Add codegen for VSX word insert/extract instructions

This patch corresponds to review:
http://reviews.llvm.org/D20239

It adds exploitation of XXINSERTW and XXEXTRACTUW instructions that
are useful in some cases for inserting and extracting vector elements of
v4[if]32 vectors.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275215 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed