CXXRTL: assert '!for_debug' failed with `write_cxxrtl -g4`

[jfng]

Version

Yosys 0.38+88 (git sha1 d5934357f, gcc 13.2.1 -fPIC -Os)

On which OS did this happen?

Linux

Reproduction Steps

Create the following repro.il file:

attribute \cxxrtl_blackbox 1
attribute \blackbox 1
module \jtag_model
  wire output 3 \tms
end

module \sim_top
  wire \jtag_tms
  cell \jtag_model \U$0
    connect \tms \jtag_tms
  end
end

Run yosys repro.il -p "write_cxxrtl -g4"

Expected Behavior

A CXXRTL output.

Actual Behavior

ERROR: Assert `!for_debug' failed in backends/cxxrtl/cxxrtl_backend.cc:1522.

[jfng]

This error does not occur with:

• any -O level below 5 (e.g. -O4 -g4)
• any -g level below 4 (e.g. -O6 -g3)

[whitequark]

That looks like a bug in the repro as you're connecting a 3-bit port to a 1-bit wire without any adjustment.

By this I mean that the IR seems invalid to me and a correctly functioning frontend and all of the trusted components (like manually entered IR for blackboxes) should not be generating this IR.

[povik]

That looks like a bug in the repro as you're connecting a 3-bit port to a 1-bit wire without any adjustment.

The 3 happens to refer to the port ID, not the width of the port.

[whitequark]

Oh. I really don't like RTLIL U_U

[whitequark]

I'm not actually sure whether this is valid input for the CXXRTL backend as-is (it might be over-minimized?) but I'd have to investigate why it fails and think about the semantics of this.

[gatecat]

The assert was removed in https://github.com/YosysHQ/yosys/commit/d903f47d41cad38ab80c74095ece198afb947ae7, not sure if the issue is still relevant.

[whitequark]

I think this should be fixed now.