Barrel Shifter/Rotater for Vec

[ZenithalHourlyRate]

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• Did you add appropriate documentation in docs/src?
• Did you state the API impact?
• Did you specify the code generation impact?
• Did you request a desired merge strategy?
• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• new feature/API

API Impact

This does not affect the current API.

This adds BarrelShifter API for Vec. This reduces latency when shifting a whole UInt by byte/word instead of by bits. (e.g. aes32esi needs to select one byte among four bytes. This is used in chipsalliance/rocket-chip#2950)

Backend Code Generation Impact

Does this change any generated Verilog? No

Desired Merge Strategy

• Rebase

Release Notes

• Shift/Rotate for Vec is more efficiently now via experimental BarrelShifter API

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels?
• Did you mark the proper milestone (Bug fix: 3.4.x, [small] API extension: 3.5.x, API modification or big change: 3.6.0)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you mark as Please Merge?

[CLAassistant]

All committers have signed the CLA.

[sequencer]

LGTM with some nitpicks on documentation and API decision.
I have been looking forward to a configurable Barrel Shifter implementation to have a fine granular control to dynamic shifting. Thanks @ZenithalHourlyRate

[ekiwi]

I like it, but I am wondering if this should be part of a new chisel3.std package? Since it is a useful functionality to have, but not necessarily part of the core language?

[sequencer]

@ekiwi Agree, I also want this to live in the chisel3.std(I may also wanna move more utils to that package.)

[ZenithalHourlyRate]

Fixed format issue

[sequencer]

@ZenithalHourlyRate I just helped you fix the build.sc and rebased it to master, you may need to tune the build.sbt to make CI happy.

[ZenithalHourlyRate]

@ekiwi Where should I put the test, in integration-tests/src/test/scala/chiselTests/std/ or stdlib/test/scala/chisel3/std ?

[ZenithalHourlyRate]

I tried to put the test in stdlib/test/scala/chisel3/std following #2441, this time both compile and test work for mill

mill chisel3\[_\].stdlib.compile
mill chisel3\[_\].stdlib.test

but for sbt, when I

sbt ++2.13.6 standardLibrary/compile
sbt ++2.13.6 standardLibrary/test

sbt would complain that not found: object chiseltest, it seems that the dependency is missing, but I can find it in build.sbt https://github.com/chipsalliance/chisel3/blob/4a78369a67ad0adfb5e8721f59e6b0b84e690e68/build.sbt#L253

I do not know how to fix this sbt issue. Is there any suggestion on this?

[ZenithalHourlyRate]

This time all compile and test worked for sbt and mill

sbt ++2.13.6 standardLibrary/compile
sbt ++2.13.6 standardLibrary/test
mill chisel3\[_\].stdlib.compile
mill chisel3\[_\].stdlib.test

Test is in stdlib/src/test now

[sequencer]

Small nitpick. Generally LGTM.

[sequencer]

with squash and not backport, if any concerns, we can revert it.