Signals with private names

[whitequark]

In some cases it is desirable to create a signal with a name that doesn't show up in the waveform viewer, such as when a signal is created to hold the results of intermediate computations, or to change shape, and it would just add noise. I propose adding a notion of a "private signal name".

I suggest changing naming rules so that Signal(name="") creates a signal with a private name. Such a signal is translated to a private wire in RTLIL (with a $\d+ name), doesn't get displayed in the waveform viewer, and so on.

---

The FSM ongoing signals (not the state signal) should be changed to have private names in the 0.5 milestone.

[tpwrules]

Would this also be the default for some signals generated by Amaranth, or would a user have to create such a private signal explicitly?

[whitequark]

Would this also be the default for some signals generated by Amaranth

Only the ones that are implementation details (currently just with m.FSM() but I think we might have others later).

[tpwrules]

I think this should be straightforward, I will try to cook up an implementation this weekend and update by Monday.

[whitequark]

Thanks!