Re: auto predicating branches

On 2025-04-20 2:44 a.m., Robert Finch wrote:

>
I have several examples where My 66000 with only 32-GPRs compiles
to fewer instructions than RISC-V with 32+32 registers.
>
I have other examples where My 66000 does not need spill/fill code
and RISC-V does, too.
>

>
I like having the extra register files, it is just a personal
programming convenience. It reduces the pressure on the general-purpose
register file.

>
Universal constants also reduces pressure both on ISA on the GPRs, and
on executing instructions.

 Stark uses a four bit code to encode where on the cache line a large constant is located. The assembler just piles them up at the end of the cache line. Sometimes space is wasted if an instruction with a constant will not fit on the cache line. I think it is <6%. It has got to be close to the finagling that RISCV does for larger constants.

>
>
Changing the capital R in RISC into a lower case r ?!?

 Lower case r?
 Been working on predicate logic tonight. Predicate shadow is limited to six instruction due to a limited mask size. Can always code more of the same predicate to skip more instructions.
 I have the code searching the ROB backwards until a predicate instruction is encountered, to determine if there is a predicate. Searching fewer instructions helps. Probably not the cleverest way of doing things, sort of brute force.

Got hung up on the predicate logic and decided to tackle something easier but similar. Having branches automatically convert into predicates when they branch forward a short distance <7 instructions. The instructions are likely already in the pipeline since it is only one or two instruction groups.
Ran into issues with the predicate logic and the LOC were just exploding. Better to work on improving the branches first, predicates might fall out later.