[llvm-dev] Manipulating DAGs in TableGen

[Paul C. Anagnostopoulos via llvm-dev]

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.
>
>Cheers,
>Nicolai