[llvm-dev] Clang-12 fails build on MacOS

[Steven Wu via llvm-dev]

The error is basically:
:info:build CMake Error: failed to create symbolic link '/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-12/clang-12/work/build/projects/compiler-rt/lib/builtins/outline_atomic_helpers.dir/outline_atomic_ldadd2_1.S': file already exists

Looks like this is caused by https://reviews.llvm.org/D93178 <https://reviews.llvm.org/D93178>. It seems that when you build multiple arm64 slice (in this case, arm64 and arm64e), the LSE builtin will be generated twice. In the rare case that when two same `cmake -E create_symlink` running at the same time, you get that error. Before the change, it was compiling using clang so you don't get this weird race condition.

You can probably workaround by manually set `DARWIN_osx_BUILTIN_ARCHS` to remove `arm64e` since you don't really need that. At the meantime, can you file a bug report to bugs.llvm.org <http://bugs.llvm.org/>?

Steven


> On Jul 16, 2021, at 12:24 PM, Blumenthal, Uri - 0553 - MITLL via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> It seems there’s a problem with parallel builds, but I don’t really know the cause of the problem. You can see the screen log and the complete build log here: https://trac.macports.org/ticket/63026#comment:5 <https://trac.macports.org/ticket/63026#comment:5>
>  
> iMac Pro (Intel Core i9, 10 cores), MacOS Big Sur 11.4, Xcode-12.5.1, clang-12.0.1.
>  
> It would be great if this problem is resolved.
>  
> Thanks!
> --
> Regards,
> Uri Blumenthal                              Voice: (781) 981-1638 
> Secure Resilient Systems and Technologies   Cell:  (339) 223-5363
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>  
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