rustc_target: RISC-V: add base I-related important extensions by a4lg · Pull Request #138823 · rust-lang/rust (original) (raw)

Of ratified RISC-V features defined, this commit adds extensions satisfying following criteria:

• Formerly a part of the I extension and splitted thereafter (now ratified as I + Zifencei + Zicsr + Zicntr + Zihpm) or
• Dicoverable from newer versions of the Linux kernel and implemented as a part of std_detect's feature (Zihintpause) and
• Available on LLVM 18.

This is based on the latest ratified ISA Manuals (version 20240411).

LLVM Definitions:

• Zifencei
• Zicsr
• Zicntr
• Zihpm
• Zihintpause

Additional (1):
One of those, Zicsr, is a dependency of many other ISA extensions and this commit adds correct dependencies to Zicsr.

Additional (2):
In RISC-V, G is an abbreviation of following extensions:

• I
• M
• A
• F
• D
• Zicsr (although implied by F)
• Zifencei

and all RISC-V targets with the G abbreviation and targets for Android / VxWorks are updated accordingly.

Note:

Android will require RVA22 (likely RVA22U64) and some more extensions, which is a superset of RV64GC. For VxWorks, all BSPs currently distributed by Wind River are for boards with RV64GC (this commit also updates riscv32-wrs-vxworks though).

This is the version 4.
Ztso in the original proposal is removed on the PR version 2 due to the minimum LLVM version (non-experimental Ztso requires LLVM 19 while minimum LLVM version of Rust is 18). This is not back in PR version 3 and 4 after noticing adding Ztso is possible by checking host LLVM version because PR version 3 introduces compiler target changes (and adding more extensions would complicate the problems; sorry Zihintpause).

Version 4:

• Fixed some commit messages,
• Added Android / VxWorks targets to imply G and
• Added an implication from Zve32x to Zicsr (which makes all vector extension subsets to imply Zicsr)
  since rustc_target: Add more RISC-V vector-related features and use zvl*b target features in vector ABI check #138742 is now merged.

Related:

• Tracking issue for RFC 2045: improving #[target_feature] #44839
  (riscv_target_feature)
• Tracking Issue for RISC-V Ratified Extensions Intrinsics #114544
  (This PR can be a prerequisite of resolving a part of that tracking issue)
• rustc_target: Add more RISC-V vector-related features and use zvl*b target features in vector ABI check #138742
  (Touches the same place and vector extensions depend on Zicsr)

NOT Related but linked:

• Some -Ctarget-features must be restrained on RISCV #132618
  (This PR won't be blocked by this issue since none of those extensions do not change the ABI)

@rustbot r? @Amanieu
@rustbot label +T-compiler +O-riscv +A-target-feature