Need for Darwin.llvm build_config

[mathomp4]

Homebrew now has flang 22 which makes it nice and easy to get on macOS.

However, at the moment, ESMF doesn't have a Darwin.llvm.default setup in build_config.

I'm going to try and see if I can get something based on trying to combine Linux.llvm.default and Darwin.gfortranclang.default.

But my fear is I'll need the help of the ESMF Build System Guru @theurich .

[mathomp4]

I do have something...sort of working:

❯ rg 'Found.*tests' makecheck.appleclang-flang-22_openmpi-5.0.10.esmf.log
9422:Found 9070 non-exhaustive multi-processor unit tests, 9052 passed and 18 failed.
10346:Found 51 multi-processor system tests, 51 passed and 0 failed.
10351:Found 51 multi-processor system tests, 51 passed and 0 failed.
10356:Found 9070 non-exhaustive multi-processor unit tests, 9052 passed and 18 failed.

but it is not very generic. I'm working to building MAPL to make sure it works as a more external library.

Once I can say it's not complete garbage, I'll point to my test example

[theurich]

@oehmke and @mathomp4 I think it would be very useful if we could set up LLVM 22 on ESMF's Darwin test system Fairy. Sounds like Homebrew would make that relatively straight forward.

On the other hand I seem to remember that @billsacks set up the configurations on Fairy using Spack. That might give us a more consistent setup? Anyway, having an "in-house" Darwin.llvm.default system would be great. Also of course for nightly testing.

[billsacks]

@theurich - yes, Fairy is set up using Spack, with details here. If it's possible to do this through Spack, that feels much preferable: I have no idea how this spack setup would interact with a homebrew setup.

Let me know if you'd like my involvement in this.

[theurich]

@billsacks thank you for your input. Having you involved in this would be fantastic, since you have done the initial setup on Fairy. Tagging @anntsay for awareness, and also to make final decision on who might be available. Is your thinking that setting up LLVM 22 on Fairy, using Spack, would be quick and painless?

[mathomp4]

It looks like the spack llvm 22.1.0 PR is currently waiting for patch.

As for my attempt (with Claude's help), you can see it here.

The ugliest bits are:

# Dynamically find Flang's lib dir to bypass broken libs.llvm script
FLANG_PREFIX := $(shell brew --prefix flang 2>/dev/null || echo /opt/homebrew/opt/flang)

############################################################
# Link against libesmf.a using the F90 linker front-end
#
ESMF_F90LINKLIBS += -L$(FLANG_PREFIX)/lib -lflang_rt.runtime -lc++

############################################################
# Link against libesmf.a using the C++ linker front-end
#
ESMF_CXXLINKLIBS += -L$(FLANG_PREFIX)/lib -lflang_rt.runtime -lc++ -lm

and for all I know, those are only good for "flang-from-brew". Flang built/retrieved from another way might be different!

But that library does seem...plausible.

[theurich]

It looks like the spack llvm 22.1.0 PR is currently waiting for patch.

Okay certainly will wait for this PR before attempting installation via Spack. Thanks!

[billsacks]

Is your thinking that setting up LLVM 22 on Fairy, using Spack, would be quick and painless?

Hah! No, not at all!

[theurich]

Just an update that spack/spack-packages#3551 is merged!