Print warning when extractor is too wide or narrow

[albertchen-sifive]

Contributor Checklist

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Type of Improvement

• bug fix

API Impact

none

Backend Code Generation Impact

none

Desired Merge Strategy

Squash

Release Notes

Warn when dynamic extract index is too wide or too narrow.

Reviewer Checklist (only modified by reviewer)

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[jackkoenig]

Looks good but I have some comments. I'd also like to see an FAQ page for these errors to tell people how to resolve them (using .pad or a bit extract, or both in the case of a generator where the width may be too large or too small under different circumstances).

[albertchen-sifive]

I noticed that the error message for zero-width extractee is printing twice. once from the dynamic index and then again when it does (this >> x)(0)

[error] src/test/scala/chiselTests/UIntOps.scala:412:18: Cannot extract from zero-width UIntOpsSpec_Anon.in: IO[UInt<0>]
[error] src/test/scala/chiselTests/UIntOps.scala:412:18: Cannot extract from zero-width
[error] There were 2 error(s) during hardware elaboration.

Is it fine to change the message back to just Cannot extract from zero-width so that they dedup?

[mwachs5]

This relates to #2946