[llvm-dev] Manipulating DAGs in TableGen

[Madhur Amilkanthwar via llvm-dev]

On Tue, Oct 13, 2020 at 8:07 PM Paul C. Anagnostopoulos <paul at windfall.com>
wrote:

> Nicolai:
>
> If we have two operators to get and set DAG operator/operands, does it
> make sense to add to more operators to get/set the $names of operands? They
> would still specify the operand by integer index.
>
> At 10/13/2020 10:16 AM, Nicolai Hähnle wrote:
> >On Tue, Oct 13, 2020 at 10:47 AM Madhur Amilkanthwar
> ><madhur13490 at gmail.com> wrote:
> >> What do you guys think about the below enhancements?
> >>
> >> 5. !getdagrestype(dag [, index]) - Returns type of result value. If the
> DAG computes multiple values then return type of 'index'th result.
> >>
> >> 6. !setdagrestype(dag target_dag, type T [, index]) - Set return type
> of target_dag to T. Use of 'index' is as in 5.(Coupled with the existing
> (or enhanced?) foreach construct we can construct multiple DAGs with
> different return types.)
> >>
> >> .7 !setdagchild(dag target_dag, dag new_dag, index) - Set child 'index'
> numbered of target_dag to new_dag. I think this is more or less similar to
> 3 you suggested but I feel it is more convenient and concise.
> >>
> >> 8. !setdagchildcond(dag target_dag, dag new_dag, index, {C++ code}) -
> Similar to 7 above but do it only if the C++ code returns true. This is
> useful to check if the result type of `new_dag` and that of the operand
> type of 'index' child of 'target_dag' are compatible. Users can define
> compatibility using C++ code. For example, it is okay to set dag even if
> there is mismatch between signedness of types.
> >
> >All of these sound like operations that are specific to TableGen
> >backend interpretations of what a DAG means. This discussion is about
> >!ops which are a part of the TableGen frontend, so I don't think any
> >of these apply here.
>

I am not sure why you say so. Isn't 7 and 8 above somewhere similar to
*!con* already offered by the language?  !con allows you to concatenate two
DAGs, 5 allows you to connect two DAGs to form a bigger DAG. You may be
able to achieve the same today with existing the language constructs but I
don't see a concise way to do this.

5 and 6 are subject to debate but since it's a language an addition like
this could be useful.


>Cheers,
> >Nicolai
>
>

-- 
*Disclaimer: Views, concerns, thoughts, questions, ideas expressed in this
mail are of my own and my employer has no take in it. *
Thank You.
Madhur D. Amilkanthwar
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