Replace -xCORE-AVX2 with -mavx2

[dougiesquire]

We currently have -xCORE-AVX2 being set in a few of our SPRs (see below). These flags are CPU restrictive and have prevented users from building our models with Intel compilers on other HPC systems (e.g. NeSI and Archer2). The recommendation from the software transformation team (i.e. @manodeep) is to replace these flags with -mavx2, which will still allow AVX2 instructions but won't prevent running on other CPUs.

We are in the process of replacing -xCORE-AVX2 with -mavx2 where the flag is used in CMake build systems, but some changes to SPRs are also required:

• mom5: in the MakefileBuilder (cmake is default)
• access-mocsy: in the MakefileBuilder (cmake is default)
• cice5: in the MakefileBuilder (cmake exists, but makefile is still default)
• cice4: MakefileBuilder only
• oasis3_mct: MakefileBuilder only

Note, oasis3_mct and cice5 actually set -axCORE-AVX2 which does allow running on different CPUs, but @manodeep still recommends changing to -mavx2.

[dougiesquire]

Note, we also have -xCORE-AVX512 being set in a few SPRs. Mostly these are being set when building ACCESS-ESM1.5 (e.g. in cice4, oasis3_mct, mom5), but I think um7 uses -xCORE-AVX512 for ACCESS-ESM1.6.

Should we change this @manodeep?

[dougiesquire]

I'm finding that replacing -xCORE-AVX2 with -mavx2 in the ACCESS-OM2 stack degrades performance (~12%).

Should we just be removing these flags altogether and letting Spack set the architecture-specific stuff via target

From the Spack docs:

When a spec is installed, Spack matches the compiler being used with the microarchitecture being targeted to inject appropriate optimization flags at compile time. Giving a command such as the following:

spack install zlib target=icelake %gcc@14

will produce compilation lines similar to:

/usr/bin/gcc-14 -march=icelake-client -mtune=icelake-client -c ztest10532.c
/usr/bin/gcc-14 -march=icelake-client -mtune=icelake-client -c -fPIC -O2 ztest10532.
...

where the flags -march=icelake-client -mtune=icelake-client are injected by Spack based on the requested target and compiler.