Implementing a new LLVM based toolchain

[Crivella]

Compilers

• New llvm.py compiler taken from the original clang.py and unifying it with flang
  • Now allows defining a list of unsupported flang compiler options based on the passed LLVM version which will be excluded, from the compiler flags

Toolchains

• LLVMtc: Similar to GCC uses bot GCCcore and SYSTEM as a subtoolchain
• Lfbf equivalent of Gfbf
• Lompi equivalent of Gompi
• LFoss equivalent of Foss
  • Does not have the OpenBLAS child class as in Foss it is used only for toolchains older than 2021.0

TODO

• Extensively investigate+test the comments related to the compiler flags on the old clang.py compiler
• Extensively test interplay of compilations with libstdc++ and possibly libc++
• Interplay between LLVM and CUDA / ROCm
• Possibly have variants of LLVM like ROCm-LLVM work through the same toolchain

[Crivella]

d6fe4f9

Apparently some tests were failing because xlompi is an actual toolchain and the test was using 'x' as an prefix to check that a toolchain with wrong name should not be found

[Thyre]

I honestly don't really like the name LLVMtc. This deviates from the naming we have for GCC & Intel, and even the proposed name for the NVHPC split. In addition, people might be confused by the abbreviation, if they're not familiar with EasyBuild.

Should we go with llvm-compilers, similar to what we have with intel-compilers and nvidia-compilers? We could use this same naming scheme for other toolchains going forward (rocm-compilers, aocc-compilers, ...).

[Crivella]

I am open to suggestions for the naming scheme.

I wanted to go for LLVM but that would conflict with the the EC for LLVM.
I think at the time i thought about renaming LLVM to LLVMcore, but i think that can be confusing toward being an LLVM.so only build without any additional project

[Thyre]

I think using <compiler-name>-compilers as a general rule sounds the best for me. GCC deviates from this, but I don't think we should change this one, given that it's around for basically forever.

But certainly open for other options. Maybe worth discussing in one of the bi-weekly meetings?