Getting bit numbers in TableGen interfaces.

Hi,

I have the following code in TableGen language:

bits<32> insn;
bits<4> CRm = {0, 0, 1, 1};
let insn{11-8} = CRm;

Is there a way to get the bit numbers (in this case 11-8, to which a
list of constant bits (`CRm`) is assigned) using `Record` interfaces?
When I iterate bits of `insn`, it doesn’t contain the `VarBitInit` of
`CRm`, because `insn` consists of the `BinInit` objects.

Thanks,
Ivan