Make CheckWidths accept zero-width UIntLiterals

[jackkoenig]

Fixes #508

Release notes: Zero-width literals with value zero are now allowed.

[jackkoenig]

This change seems to lead to a zero-width Vec issue in the Chisel tests. Looking into it

[jackkoenig]

(Well I think this one combined with the one where Chisel emits zero width UInts)

[donggyukim]

@colinschmidt Can you confirm this works?

[jackkoenig]

Here's the Chisel branch, looking in to the Chisel test failure: https://github.com/ucb-bar/chisel3/tree/one-entry-enum

[colinschmidt]

Thanks @jackkoenig I'll test with that branch and this firrtl branch

[colinschmidt]

Hmm I got a bunch of these errors:

======== Starting Transform CheckWidths$ ========
[error] (run-main-0) firrtl.passes.PassExceptions:
[error] firrtl.passes.CheckWidths$TailWidthException:  @[Decoupled.scala 221:40:[email protected]]: [module FinishQueue] Parameter 1 in tail operator is larger than input width 1.
[error] firrtl.passes.CheckWidths$TailWidthException:  @[Decoupled.scala 221:40:[email protected]]: [module FinishQueue_1] Parameter 1 in tail operator is larger than input width 1.
[error] firrtl.passes.CheckWidths$TailWidthException:  @[Decoupled.scala 221:40:[email protected]]: [module FinishQueue_2] Parameter 1 in tail operator is larger than input width 1.
[error] firrtl.passes.CheckWidths$TailWidthException:  @[Decoupled.scala 221:40:[email protected]]: [module Queue_16] Parameter 1 in tail operator is larger than input width 1.
[error] firrtl.passes.CheckWidths$TailWidthException:  @[Decoupled.scala 221:40:[email protected]]: [module Queue_17] Parameter 1 in tail operator is larger than input width 1.
[error] firrtl.passes.CheckWidths$TailWidthException:  @[Decoupled.scala 221:40:[email protected]]: [module Queue_127] Parameter 1 in tail operator is larger than input width 1.

[jackkoenig]

It seems like there might be some hidden zero-width wire problems in Firrtl, perhaps we should just patch Chisel by not emitting zero-width for 1-entry Enums and at least fix THAT problem

[jackkoenig]

I added a testcase that currently fails so that a fix for it (and possibly other issues) can accompany this change.

[azidar]

Any updates on this? Is this dated?

[jackkoenig]

No updates, I think it's a lingering problem

[ucbjrl]

All tests (FIRRTL) currently pass. I'm running regression tests with the rest of the BIG6.

[albert-magyar]

I rebased and cleaned up. The previously failing Vec test works now; should we consider merging this now @jackkoenig?