[llvm-dev] tablegen generated enums in tablegen

[Chris Sears via llvm-dev]

I'd like to store a tablegen generated enumeration in a record field/value.
Clearly this enumeration isn't available yet so it seems that a code
fragment should be the escape mechanism I need. Looking at the other
backends for examples, I see things like

    [{ return Imm >= 0 && Imm < 64; }]               // promising
    code Requires = [{ {} }];                                 // this looks
like a string
    let Requires = [{ {AArch64::FeatureETE} }].  // which is not promising

So I think that this would look something like:

    int reg_index           = -1;
    ...
    let reg_index = [{ return XX::R8; }];               // or
    let reg_index = [{ {XX::R8} }];

However, then I get errors of the form:

    error: Value 'reg_index' of type 'int' is incompatible with initializer
'[{ {XX::R8} }]' of type 'code'
    error: Value 'reg_index' of type 'int' is incompatible with initializer
'[{ return XX::R8; }]' of type 'code'

Is there a way of doing this? I don't understand TableGen casting but is
that necessary?
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