[llvm] [TableGen][Decoder] Decode operands with zero width or all bits known (PR #156358)

[Rahul Joshi via llvm-commits]

jurahul wrote:

The description does not say anything about case 2. Can we say a line or 2 about it as well for completeness? I am guessing the constant bits are passed in as is to the decode function.

https://github.com/llvm/llvm-project/pull/156358