[FIRRTL] Incorrect multbit mux canonicalization
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Description
See https://github.com/llvm/circt/pull/6382#issuecomment-1802466614https://github.com/llvm/circt/pull/6382#issuecomment-1802466614https://github.com/llvm/circt/pull/6382#issuecomment-1802466614
```mlir
firrtl.circuit "UselessIndexBit"{
firrtl.module @UselessIndexBit(in %a: !firrtl.uint<3>, out %b: !firrtl.uint<4>, in %c: !firrtl.uint<4>, in %d: !firrtl.uint<4>, in %e: !firrtl.uint<4>) {
%0 = firrtl.multibit_mux %a, %c, %c, %e, %c, %c, %c : !firrtl.uint<3>, !firrtl.uint<4>
firrtl.strictconnect %b, %0 : !firrtl.uint<4>
}
}
```
Contributor guide
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reading the linked comment on pull request 6382 and reproducing the provided FIRRTL MLIR example involving firrtl.multibit_mux. Determine the expected canonical form from that discussion; done means the example no longer produces the incorrect multibit mux canonicalization.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- cpp
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 25/100