DAG combine incorrectly optimize (i32 vextract (v4i16 load $addr), c) to

DAG combine incorrectly optimize (i32 vextract (v4i16 load $addr), c) to
(i16 load $addr+c*sizeof(i16)) and replace uses of (i32 vextract) with the
i16 load. It should issue an extload instead: (i32 extload $addr+c*sizeof(i16)).

rdar://11035895

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152675 91177308-0d34-0410-b5e6-96231b3b80d8