RFC for RVV intrinsic API proposal

[issuehsu]

Hi,
Kai wrote the RFC for RVV intrinsic API proposal based on our current discussion.
Any suggestion and feedback are welcome.

https://github.com/sifive/rvv-intrinsic-doc/blob/master/rvv-intrinsic-rfc.md

[rofirrim]

Thanks @Hsiangkai for putting this RFC together.

I understand that vcopy_v is needed when we want to copy only VL elements of the vector. My understanding is that a plain C assignment would copy it all (so the vector vehaves like a regular value here).

Regarding a question posed by @zakk0610 during our internal discussion, I understand reinterpret intrinsics will allow converting mask types to/from other integer types of LMUL=1. Also I presume reinterpret casts will allow reinterpretation between different types of the same LMUL (e.g. i32m1 and i64m1), won't it?

[kito-cheng]

Oh... in fact SiFive’s Implementation vcopy is same as assignment in C, which is VL aware, the same issue for vector type is pointer dereference vs unit stride load/store, we implement its in VL aware too.

We might need to create a new issue to discuss about the behavior and limitation for vector type.

[Hsiangkai]

If we support C assignment, should we support other C operators for scalable vector types? We should list the supported C operators in the RFC. In addition, what is the operating scope of C operator, VLMAX or vl? In SiFive's implementation, it is vl. The semantics is aligned to intrinsics design without vl argument.

[zakk0610]

I agree we should support " converting mask types to/from other integer types of LMUL=1".
But I could not image why user want to reinterpretation between different types of the same LMUL, it is strange usage.

edited: we could discuss it in https://github.com/sifive/rvv-intrinsic-doc/issues/12

[Hsiangkai]

Oh... in fact SiFive’s Implementation vcopy is same as assignment in C, which is VL aware, the same issue for vector type is pointer dereference vs unit stride load/store, we implement its in VL aware too.

We might need to create a new issue to discuss about the behavior and limitation for vector type.

We could discuss it in https://github.com/sifive/rvv-intrinsic-doc/issues/13.

[Hsiangkai]

We will discuss the RFC in other issues.