[SelectionDAG] Add ability for computeKnownBits to peek through bitcasts from 'large element' scalar/vector to 'small element' vector.

Extension to D27129 which already supported bitcasts from 'small element' vector to 'large element' scalar/vector types.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@289329 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed