Scala 3 Cross-Compilation Support

[vighneshiyer]

Cross-compile firrtl for Scala 2.13 and 3. I'm slowing adding the necessary changes to this PR to see when a test breaks.

[ekiwi]

Looks good to me as long as it passes CI

[ekiwi]

The CI needs to also run the Scala 3 version.

[vighneshiyer]

https://github.com/ucb-bar/firrtl2/actions/runs/4931578837/jobs/8813751741?pr=14#step:9:1198

It seems that either there is a regression in yosys, or the constant propagation pass has a real bug that wasn't caught with an old version of yosys. I will run equivalence checking using Jasper to figure out which one.

[ekiwi]

It seems that either there is a regression in yosys, or the constant propagation pass has a real bug that wasn't caught with an old version of yosys. I will run equivalence checking using Jasper to figure out which one.

That is a good idea. I think yosys equivalence checks can be a bit brittle sometimes.

[vighneshiyer]

firrtl_ops.zip

Run jasper with jg -allow_unsupported_OS -no_gui -sec -tcl equiv_check.tcl.

INFO: Verification result is: NOT 'proven'. The designs are NOT equivalent.

There is a bug in the firrtl pass, but I'm not sure where to start debugging it.

[ekiwi]

There is a bug in the firrtl pass, but I'm not sure where to start debugging it.

Can you compare to the firrtl output before you applied your changes? Does that pass with Jasper?

[vighneshiyer]

The firrtl output (Ops_custom.v and Ops_ref.v) before and after I applied my changes is identical. CI also confirms that the equivalence check passed before and after my changes on an old version of yosys, but a new version of yosys catches the non-equivalence.

[ekiwi]

The firrtl output (Ops_custom.v and Ops_ref.v) before and after I applied my changes is identical. CI also confirms that the equivalence check passed before and after my changes on an old version of yosys, but a new version of yosys catches the non-equivalence.

If that is the case then I would suggest that you don't update the yosys version in this PR since the failure is unrelated. Once we land Scala 3 support you can make another PR that updates the yosys version and we can discuss debugging the bug on that PR.

[vighneshiyer]

Sounds good, I reverted the OSS CAD suite version bump, and added Scala 3 to the CI matrix. I expect 2 JSON parser related tests to fail in CI for Scala 3, and we can discuss how to fix those soon.

[vighneshiyer]

Looks like CI hits the 2 JSON-related unittest failures. This seems to be an issue in how json4s handles extraction of generic types (e.g. List). The issue is documented here: json4s/json4s#1035

What do you suggest? Should I try using a different JSON library, or is the surface that touches too large? If there are no/few annotations that use these features, perhaps these specific unittests can be ignored for Scala 3?

[ekiwi]

I removed the JSON tests. I think the feature tested there is rare. Mostly used by Firesim.