[PowerPC] Improvements for BUILD_VECTOR Vol. 1

This patch corresponds to review:
https://reviews.llvm.org/D25912

This is the first patch in a series of 4 that improve the lowering and combining
for BUILD_VECTOR nodes on PowerPC.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@288152 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed