Clean up my own mess.

Clean up my own mess.
X86 lowering normalize vector 0 to v4i32. However DAGCombine can fold (sub x, x) -> 0 after legalization. It can create a zero vector of a type that's not expected (e.g. v8i16). We don't want to disable the optimization since leaving a (sub x, x) is really bad. Add isel patterns for other types of vector 0 to ensure correctness. It's highly unlikely to happen other than in bugpoint reduced test cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48279 91177308-0d34-0410-b5e6-96231b3b80d8