TRELLIS_SLICE unsupported error

[ECP5-PCIe]

Instantiating a TRELLIS_SLICE on the ECP5 as in https://gist.github.com/newhouseb/784cc0c24f8681c3224c15758be5d1b8 results in
ERROR: cell type 'TRELLIS_SLICE' is unsupported
It did work several months ago, was it replaced by a different primitive?

[Mecrisp]

I am also missing TRELLIS_SLICE which I used for implementing a ring oscillator. Is a different LUT4 primitive available instead? A pointer to the currently available primitives would be helpful.

[gatecat]

Following the big split-slice reshuffle, the best option in general is a CCU2C for carries or a LUT4 for LUTs. BEL constraints will work on the latter but are a bit more complex on the former (there might be a way to make it work but that will need some investigation).