[Comb] i0 in concat is not folded
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Description
```bash
hw.module @top(in %in1 : i2, in %in2 : i0, out out : i2) {
%0 = comb.concat %in1, %in2: i2, i0
hw.output %0 : i2
}
$ circt-opt -canonicalize
hw.module @top(in %in1 : i2, in %in2 : i0, out out : i2) {
%0 = comb.concat %in1, %in2 : i2, i0
hw.output %0 : i2
}
```
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- 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.
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Research direction
Start by reproducing the example with circt-opt -canonicalize and inspect the comb.concat operation involving the i0 input. Trace the canonicalization or folding entry point for comb.concat. Done means the zero-width input is folded away and the shown module is simplified as expected.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- cpp
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100