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

[Rahul Joshi via llvm-commits]

jurahul wrote:

> > Would it also make sense to add this comment?
> > ```
> > // Represents a span of bits in the instruction encoding that's based on a span
> > // of bits in an operand's encoding.
> > //
> > // Width is the width of the span.
> > // Base is the starting position of that span in the instruction encoding.
> > // Offset if the starting position of that span in the operand's encoding.
> > // That is, bits {Base + Width - 1, Base} in the instruction encoding form
> > // bits {Offset + Width - 1, Offset} in the operands encoding.
> > struct EncodingField {
> > ```
> > 
> > 
> >     
> >       
> >     
> > 
> >       
> >     
> > 
> >     
> >   
> > If you want to incorporate it here, or I can create a separate PR as well.
> 
> Please create a separate PR and also borrow that comment we discussed so that this PR gets smaller after rebasing.

Sounds good, will do,

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