[Feature Request] Instancing primitives as modules

Convenience feature request.

Right now FIRRTL primitives require a different syntax than instancing Module. Would it be possible to add support for instancing and wiring up primitives like a Module?

Reasoning: our language infrastructure treats primitives like user-defined modules, thus emitting FIRRTL either requires special casing primitive modules or defining wrapped version of primitives as modules.

Are there any downsides to this approach? Presumably one could write a pass that replaces instances of primitive modules using the function-call-style syntax. Or the other way around (the special primitive syntax would then be considered sugar on top of normal module instantiation). Could this affect any FIRRTL passes?

Example:

circuit Example :
  module my_module : 
    input a : UInt
    input b : UInt
    output c : UInt

    inst my_adder of add
    my_adder.in0 <= a
    my_adder.in1 <= b
    c <= my_adder.out

[leonardt]

@azidar thanks, that reasoning makes sense.

[azidar]

I agree with @edwardcwang that probably the best way to do it is to emit a module with an inline annotation or to special case it in the Magma/Coreir backends.

The problem with simply added the inst syntax is that FIRRTL primops are polymorphic in their input/output types. Thus, at declaration of inst my_adder of add, we don’t know the input or output types of my_adder.