[llvm-dev] tablegen generated enums in tablegen

[Nicolai Hähnle via llvm-dev]

Hi Chris,

On Sun, Jun 28, 2020 at 9:37 AM Chris Sears via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> 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.

I don't think this is clear at all. Maybe you can explain what you're
trying to do and why simply using the enumeration fails?

[snip]
> 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'

Well, yes. [{ }] is really just more convenient syntax for strings
that are meant to contain code snippets, and you can't assign a string
to an integer :) Those code snippets aren't executed by TableGen,
they're pasted into TableGen-generated C++ and only executed at
runtime.

Why doesn't

    let reg_index = R8;

or whatever work, if R8 is an object known to TableGen?

Cheers,
Nicolai


>
> Is there a way of doing this? I don't understand TableGen casting but is that necessary?
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev



-- 
Lerne, wie die Welt wirklich ist,
aber vergiss niemals, wie sie sein sollte.