nvc: go back to using default llvm as dependency

[mitchblank]

The restriction on building against llvm@6 (later updated to llvm@7) was introduced by @jnozsc (#54741) However the issue that was referenced was fixed before 1.5.0 was released (nickg/nvc@f48c651) so when homebrew updated to 1.5.0 (#58612) this restriction should probably have been relaxed more than it was.

According to the project's README it is tested with llvm {7,8,9} so at a minimum we should probably bump its dependency to llvm@9. However, this wouldn't be enough to fix the Big Sur bottling issue.

Nothing in the project's build instructions suggests that llvm versions newer than 9.x are to be avoided these days so just switching to our default llvm (currently 11.1) instead. Seems to build and test fine.

cc @nickg, @chenrui333

[nickg]

Nothing in the project's build instructions suggests that llvm versions newer than 9.x are to be avoided these days so just switching to our default llvm (currently 11.1) instead. Seems to build and test fine.

I've tested with 11 and it works fine. Just haven't updated the README.

[SMillerDev]

Does it not work with the macOS provided LLVM?

[mitchblank]

Oh, I didn't realize that we had any formula that used the system llvm (looks like only git-delta and vlmcsd are doing this right now, at least as an explicitly declared uses_from_macos dependency) I can give it a try.

[SMillerDev]

Most of them don't declare it explicitly unless it can't be gcc. (Which would be the default on Linux)

[Bo98]

If it requires stuff like libLLVM then system LLVM won't work. The use of llvm-config suggests to me that may be the case (system LLVM does not have llvm-config).

For things that only need libclang, system LLVM can work - but usually requires extra steps in the build system to find it (since there's no clang-config).

[nickg]

If it requires stuff like libLLVM then system LLVM won't work. The use of llvm-config suggests to me that may be the case (system LLVM does not have llvm-config).

It uses libLLVM for code generation so won't work without that.

[mitchblank]

Yeah, it doesn't seem like llvm API is exposed in any of the SDKs at all, e.g. find /Applications/Xcode.app -name ExecutionEngine.h returns zero results.

@SMillerDev -- could you explain what you want more clearly. Just so we're on the same page, the llvm dependency is not due to the project preferring clang over gcc; this is a project that builds on top of the LLVM compiler framework itself. It doesn't seem that's possible unless we take the llvm formula dependency.

[carlocab]

Thanks, @mitchblank.

[BrewTestBot]

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