Changes to MIPS SelectionDAG:
* Added nodes VEXTRACT_[SZ]EXT_ELT to represent extract and extend in a single
operation and implemented the DAG combines necessary to fold sign/zero
extends into the extract.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191199 91177308-0d34-0410-b5e6-96231b3b80d8