OCaml backend broken with > 246 union members

[jrtc27]

In the transition from Sail 1 to 2, 89f9c0e has been lost, and the RISC-V model is close to the limit for the number of non-constant constructors generated by the OCaml backend (for the ast union representing decoded instructions). This is causing issues for the P and V extension development; see riscv/sail-riscv#132 (comment) and riscv/sail-riscv#138 (comment).

[Alasdair]

Should be fixed. I used polymorphic variants like in the commit you linked.

I also tried an alternative approach where I used the last constructor as an overflow constructor, and then generated extra variant types for the overflow cases but it seemed more complex for little benefit, assuming there are no actual issues with using polymorphic variants for this.

[martinberger]

@Alasdair is this fix already being picked up by opam?

[jrtc27]

You will need to opam pin a git clone until a new version is released

[martinberger]

You will need to opam pin a git clone

OK, this is not something we should do with the GitHub actions for the RISCV-Sail model.