[X86] getTargetShuffleInputs - add KnownUndef/Zero output support
[X86] getTargetShuffleInputs - add KnownUndef/Zero output support

Adjust SimplifyDemandedVectorEltsForTargetNode to use the known elts masks instead of recomputing it locally.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@374724 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm