LGTM.

@ceseo, you've already confirmed that LLVM_ENABLE_RUNTIMES=flang-rt and check-flang-rt work on AArch64/Linux, right?

Yes, both stage1 and stage2.

After a buildbot master restart flang-aarch64-libcxx (only) stopped working. The error message

/usr/bin/ld: flang-rt/unittests/Runtime/CMakeFiles/RuntimeTests.dir/AccessTest.cpp.o: in function `createTemporaryFile[abi:cxx11](char const*, (anonymous namespace)::AccessType const&)':
AccessTest.cpp:(.text._ZL19createTemporaryFileB5cxx11PKcRKN12_GLOBAL__N_110AccessTypeE+0x194): undefined reference to `llvm::Twine::str[abi:cxx11]() const'
clang++: error: linker command failed with exit code 1 (use -v to see invocation)

indicates an ABI issue. Maybe using the wrong headers or linking the wrong library? The issue should be with LLVM_ENABLE_LIBCXX=ON and probably would affect all LLVM_ENABLE_RUNTIMES.

@antmox FYI for flang-aarch64-libcxx.

I would start by double checking whether the flang-rt tests get built with the host compiler, or the clang that was just built, and what stdlib that/those default to. Also note that this bot does not build libcxx, it uses the host compiler's pre-built version of it.

What could be happening is that the host compiler builds the llvm libraries with libcxx, then the just built clang does not. So the flang-rt test is then trying to combine libstdc++ and libc++.

I'm not sure we want this bot to be building libcxx as well, but just as an experiment, you could also trying adding that to ENABLE_RUNTIMES and getting the just built clang to use that. Another option may be to tell the just built clang where the host's libcxx is.