Re: [RFC] RISC-V: Handle new types in scheduling descriptions

[Edwin Lu <ewlu@rivosinc.com>]

On 10/10/2023 10:11 AM, Jeff Law wrote:
> 
> 
> On 10/9/23 15:02, Edwin Lu wrote:
>> Now that every insn is guaranteed a type, we want to ensure the types are
>> handled by the existing scheduling descriptions.
>>
>> There are 2 approaches I see:
>> 1. Create a new pipeline intended to eventually abort (sifive-7.md)
>> 2. Add the types to an existing pipeline (generic.md)
>>
>> Which approach do we want to go with? If there is a different approach we
>> want to take instead, please let me know as well.
>>
>> Additionally, should types associated with specific extensions
>> (vector, crypto, etc) have specific pipelines dedicated to them?
>>
>>     * config/riscv/generic.md: update pipeline
>>     * config/riscv/sifive-7.md (sifive_7): update pipeline
>>     (sifive_7_other):
> I'd largely expect that we look at an unhandled type and first look to 
> see if its properties roughly fit into an existing define_insn_unit.  If 
> so, just add it to the existing unit.  Otherwise we end up needing to 
> create another unit.
> 
The main types that were added that are not associated with any 
extension would be "trap" type and the "cbo" (cache block operation) 
type. I have added these types to an existing pipeline in the generic.md 
file.

For the vector extension, I don't believe the existing pipelines would 
support those operations. Should I create the pipelines for now?

> What would be really interesting would be to see if we can get the 
> scheduler to indicate that it's trying to schedule an insn that doesn't 
> have a reservation.    ie, our backend tells us if we have an insn with 
> no type, the next step is to see if we have a type with no 
> units/reservations.
> 
> 
> Jeff
> 
Do you happen to have any idea on how to do this or if there are any 
existing mechanisms I should look at? I have been searching around the 
docs to see if there was any way to tell which pipeline (if any) an 
instruction is using when it is not included under a reservation without 
any luck.

Edwin