Make DAGCombiner work on vector bitshifts with constant splat vectors.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204071 91177308-0d34-0410-b5e6-96231b3b80d8
R600: Match sign_extend_inreg to BFE instructions

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204072 91177308-0d34-0410-b5e6-96231b3b80d8