Compile error on RISC-V due to .insn (llvm<=13 only)

[XieJiSS]

I'd like to create this issue to track the status of compiling .insn i 0x0F, 0, x0, x0, 0x010 directives, as well as pause / fence w,0 (these three are aliases)

Currently with clang 13.0.1, this error occurs when compiling rust:

error: unknown directive
   |
note: instantiated into assembly here
  --> <inline asm>:1:2
   |
1  |     .insn i 0x0F, 0, x0, x0, 0x010
   |     ^

error: could not compile `log` due to previous error

This is introduced by 597b8e8. I'm not saying that the commit itself has issues: rust can use this safely because rust-lang/llvm-project has cherry-picked the upstream commit to support .insn: rust-lang/rust#91528. However, for those using clang v13.0.1 (or, let's say, the unmodified llvm toolchain), they may encounter this issue during compiling. Hence, I create this issue as a explanation as well as tracking the status of llvm support for .insn.

The code should compile fine with clang 14.

[CoelacanthusHex]

In my opinion, the problem is that we are using this feature too early, I'm not saying it's wrong to use a new feature, but since almost downstream and users use rust with vanilla LLVM, we should use this feature when LLVM 14 is released.
A new tag waiting-llvm-release can be added to some pull requests that use unreleased LLVM features, we should check them out when LLVM releases a new major version instead of merging it right away.

[Amanieu]

In general the functions in std::arch are only fully supported when using Rust's custom LLVM fork. Normally this isn't a problem unless you specifically use these intrinsics in user code.

However in this case I would accept a PR to change this to a .word or equivalent since this is preventing Rust itself from compiling.

[luojia65]

The mainstream LLVM has released LLVM 14: https://github.com/llvm/llvm-project/releases/tag/llvmorg-14.0.0 .

[XieJiSS]

Thanks, I'm closing this issue as LLVM 14 can compile rust now