Tracking Issue for RISC-V Ratified Extensions Intrinsics

[coastalwhite]

This issue tracks the implementation of all the intrinsics linked to the Ratified RISC-V Extensions. The, not yet stable intrinsics are behind the riscv_ext_intrinsics nightly feature.

Steps

• [ ] Implement all extensions in stdarch
  • [x] Cryptography Extensions Volume I: Scalar & Entropy Source Instructions
  • [ ] Zkr. Entropy source extension
  • [x] Bit-Manipulation
  • [ ] Zicntr and Zihpm
  • [ ] Zicsr
  • [ ] ~Half-Precision~
  • [ ] ~Float in Integer~
  • [ ] Vector Extension
• [ ] Adjust module level documentation
• [ ] Stabilization PR

Unresolved Questions

• ~How to deal with instructions that are already dealt with by LLVM intrinsics and library features (e.g. cpop and u*::count_ones)? Include them or not?~
• Use usize for riscv32 or riscv64 specific intrinsics or use u32 and u64 respectively?
• ~How to deal with intrinsics involving immediate values?~
  1. ~Use the asm_const feature outlined in #93332.~
  2. ~Use the trick described in rust-lang/stdarch#40 and illustrated in _mm_cmpestri.~
• How to deal with CSR registers?
• Can we source titles and descriptions from the specifications? License issues?
• Dealing with the Vector extension is very difficult due to dynamically sized registers (rust-lang/rfcs#3268).

Implementation History

• rust-lang/stdarch#1453. Implements the Zk extension, except Entropy Source and Zkt.
• rust-lang/stdarch#1461. Implements the Zb extension.

• 116485. Stabilizes several RISC-V target features.

[coastalwhite]

Two additional points:

1. Upcoming PRs should use the rustc_legacy_const_generics for immediate values instead.
2. Prefer LLVM intrinsics to assembly. Intrinsics can be found here.

[coastalwhite]

Entropy Source of the Cryptographic Scalar Extension are not implemented in LLVM. Therefore, it should be implemented with inline assembly and is not part of the implemented intrinsics.

[coastalwhite]

Extensions such as Zfinx, Zdinx and Zhinx are all done by LLVM without intrinsics and therefore don't have to be done.