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v12: Support for Flang 22 #1036

@mathomp4

Description

@mathomp4

With the release of Flang 22.1.0, we can now build MAPL and pass all unit tests. So next up is GEOSgcm.

I'm currently testing this now. At a minimum we need FMS 2025 so I am starting from #933

OS Support

Linux

I can build working flang 22 with my build-llvm-flang script

macOS

I have not been able to get a working flang with build-llvm-flang. macOS is just weird enough. Luckily @cho-m is on the case in Homebrew land (see Homebrew/homebrew-core#269143). I already use their gfortran-15 so I hope they can provide us a nice easy flang in the future! → It's on homebrew!

Performance

I have been able to run. Current performance:

Compiler Model Throughput (d/d) Walltime
ifort 336.261 04:53
GNU 415.782 04:16
Flang 0 348.372 04:52
Flang 1 352.001 04:49
Flang 2 363.181 04:49

Key:

  • Flang 0: -O3 -g
  • Flang 1: -O3 -march=znver2 -g
  • Flang 2: -O3 -march=znver2 -funroll-loops -fstack-arrays -g

Latest flags on GEOS-ESM/ESMA_cmake#517

Changes Needed

All changes here are on top of #933 which has to do with removing MOM5 as at the moment, Flang 22 only works with FMS 2025 which means no more MOM5.

They are:

Need to be released/tagged

MOM5 Removal

Already released/tagged

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