stdarch
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rust-lang
RISC-V core::arch?
core::arch is missing RISC-V support, I'm specifically interested in adding support for the equivalent of rdtsc.
This was spun off https://github.com/rust-lang/stdarch/issues/40 It was mentioned there "We generally try to stick to vendor-specified intrinsics" which is an understandable but insurmountably heavy requirement.
IF there isn't a vendor-specified set of intrinsics documented and the vendor accepts to use the ones in stdarch as part of their official documentation the problem goes away.
We are at https://github.com/riscv/rvv-intrinsic-doc/tree/v0.10 now, to be noted that the specification is still changing often https://github.com/riscv-non-isa/rvv-intrinsic-doc/commits/master, but they are getting near to 1.0 now. so either we came up with a way to feed the generator available for aarch64 in an automated way or the churn would kill any number of volunteers.
We should wait for Clang to implement these builtins first, and then hope they use some form of templating that we can reuse.
The current git seems to have them https://github.com/llvm/llvm-project/tree/main/clang/test/CodeGen/RISCV/rvv-intrinsics
We could try adapting Clang's TableGen to emit our intrinsics from the same source file as Clang: https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Basic/riscv_vector.td
The discussion lately seems to focus on the vector extension but that seems unrelated the "rdtsc"-like features that prompted this filing.
I guess we could split the discussion, is the rdtsc-like feature documented somewhere?
We should figure out a way to handle LLVM's vscale in Rust, which Rust team should we consult with on this issue?
You would have to talk to the lang team about that. Scalable vectors are similar to an unsized type in that you can't read/write it directly since it has an unknown size, but on the other hand you can pass it to functions as an argument.
https://github.com/riscv-non-isa/rvv-intrinsic-doc/tree/main/rvv-intrinsic-generator now is public
We have to be careful since I think we could trip in something similar to https://github.com/rust-lang/stdarch/issues/1479 if we take the C intrinsics as-they-are.