Upgrade to Intel LLVM compilers

[DavidHuber-NOAA]

The 'classic' Intel compilers (ifort, icc, and icpc) are now discontinued and the new LLVM compilers (ifx and icx) are the only option starting with version 2024. All supported machines with working versions of the LLVM compilers should be upgraded to the LLVM suite.

[DavidHuber-NOAA]

There are some requirements that may need to be met before we can officially migrate to the LLVM compilers:

• Some NCEPLibs still need to be ported to the LLVM compilers, for instance BUFR: Add IntelLLVM (OneAPI) support NCEPLIBS-bufr#538
• Spack-stack needs to be installed on each system with the LLVM compilers

It is probable that the LLVM compilers will cooperate with 'classic' libraries, so testing can start before these ports/installations are complete. If everything is successful, then a decision should be made if the GSI should run in a mixed environment ('classic' libraries and LLVM executables).

Additionally, WCOSS2 has the following requirements

• Intel 2022 needs to be approved for production by NCO
• (Perhaps separate) the LLVM compilers need to be approved by NCO

[RussTreadon-NOAA]

@DavidHuber-NOAA : what is the status of this issue?

[DavidHuber-NOAA]

I am waiting on an LLVM-compiled spack-stack release. This should come with spack-stack 1.8.0, which is anticipated to be released in August.

[RussTreadon-NOAA]

Got it. This issue can possibly be processed along with GSI issue #662

[GeorgeGayno-NOAA]

I am waiting on an LLVM-compiled spack-stack release. This should come with spack-stack 1.8.0, which is anticipated to be released in August.

The Intel documentation says the LLVM compiler should work with libraries compiled with the 'classic' version. My preliminary UFS_UTILS tests with LLVM on Hercules are using /work/noaa/epic/role-epic/spack-stack/hercules/spack-stack-1.6.0/envs/unified-env/. Everything seems to be working (so far).

Is spack-stack 1.8.0 still targeted for August?

[DavidHuber-NOAA]

Yes, the release branch will be cut and release candidates installed on August 19th. The final installations will be made the first week of September.

[RussTreadon-NOAA]

@DavidHuber-NOAA , what is the status of this issue?

[DavidHuber-NOAA]

I will be tackling this over the next 6 months. Spack-stack 1.8.0 (just released) is proposed to be the last release to be compiled with the classic compilers.

[RussTreadon-NOAA]

Work done in this issue may benefit GSI issue #582. Issue #582 has been closed and may be revisited as work on this issue (#665) moves forward.

[RussTreadon-NOAA]

Got it, @DavidHuber-NOAA . This issue has a longer time horizon.