Instruction encodings.

[ben-marshall]

Placeholder issue for discussing instruction encodings.

Currently we are waiting for guidance from the foundation for how this process will work.

[grnewell]

Ken Dockser has volunteered to help the TG with the initial proposal for encodings.

[Xinlong-Wu]

hello everyone, Notice that almost all encodings of Instruction in K Ext are located SYSTEM, OP & OP-IMM field in ‘RISC-V base opcode map’. Could you please tell me does it will be changed in the future. Does it possible to change opcode of K Ext into reserved field in ‘RISC-V base opcode map’?

[ben-marshall]

Hi @VincenttttWu

The K extension is currently going through the opcode consistency and review process, meaning there is a chance the opcodes/encodings will change based on the recommendations which come out of that. We are hoping this won't be the case, but it's possible. You should treat the opcodes as if they will change for now.

I'm afraid I don't understand your question about changing the opcode into a reserved field of the base opcode map?

Cheers,
Ben

[Xinlong-Wu]

Cuz I am working for implement MC layer of LLVM for K Ext. So I need to decide should I use a new OPcode variable for K Ext or original one(SYSTEM, OP & OP-IMM etc.). although they have same value in this stage.

Sincerely yours,
Vincent

[ben-marshall]

Hi @VincenttttWu
Ah I see. I'm no LLVM expert so you are the best judge. I expect that whatever the K ext encodings end up being, they will be in an original opcode space like SYSTEM/OP/OP-IMM, since that's the current policy for allocating new instructions. They may change within those spaces, but I highly doubt they will be in a new greenfield / reserved space. I hope that helps?
Cheers,
Ben

[Xinlong-Wu]

Hello @ben-marshall

Sure, it's helps a lot. Thank you. )

Sincerely yours,
Vincent