sail-riscv
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riscv
D extension (double precision float) support should be a runtime option
Currently to choose between F support or F&D you need to compile the model differently - using riscv_flen_D.sail or riscv_flen_F.sail.
This is unfortunate because now to support all the different configurations you need to compile a combinatorial explosion of models:
- rv32_F
- rv32_D
- rv64_F
- rv64_D
(and 4 more if you want CHERI models)
It would be better if it was a runtime option (though this may lead to slightly less neat and type-safe code unfortunately).
@Alasdair I wonder if Sail could help here by supporting values that are compile-time constant for Sail, but runtime configurable in the generated code. I.e. instead of this:
type flen : Int = 64
type flenbits = bits(flen)
you'd have
type flen : Int = oneof(32, 64)
type flenbits = bits(flen)
and then it would compile it as if flen could be either 32 or 64 (but it must be constant). Then in the generated C/OCaml code you would be able to set it at runtime (maybe as a parameter to model_init()). This would also help for RV32/RV64.
I guess this is a large amount of work... I'm just thinking aloud. :-)
I have toyed with allowing
// Abstract type, with no value
type flen : Int
// Global constraint
constraint flen in {32, 64}
You could even do something like
type flen : Int
type have_D_ext : Bool
constraint flen in {32, 64} & implies(have_D_ext, flen == 64)
constraint flen in {32, 64}
How hard would this be to implement? Just wondering if I might have a go to save compiling separate RV32 and RV64 models.
A bit tricky as it has an effect throughout the entire compiler.
I had an implementation that went as far as the parser and type system aspects, let me see if I can drag those commits to the present.
There are also a few implementation questions, like whether to allow things like
type abstract('n: Int) : Int
because that makes sense for the type system, but we would need to instantiate that before generating C.
https://github.com/rems-project/sail/tree/abstract_types will build with a lot of warnings and probably fail if you use anything other than --just-check for the time being.