Clang -O4 Build Fails H5Tconv.c

[hyoklee]

Please check the new _Float16 code with the highest optimization levels for all compilers.

  "___truncxfhf2", referenced from:
      _H5T__conv_ldouble__Float16 in H5Tconv.c.o
ld: symbol(s) not found for architecture x86_64

See also: https://my.cdash.org/viewBuildError.php?buildid=2524289

[jhendersonHDF]

Was clang installed with homebrew on that machine? See JuliaLang/julia#52067 which is almost certainly related.

[hyoklee]

I'm using built-in Apple /usr/bin/clang.

[chenrui333]

@jhendersonHDF I am still seeing the build failure with the 12 builds (full build log, https://github.com/Homebrew/homebrew-core/actions/runs/8973996030/job/24648320497), can I get some help on it?

relates to Homebrew/homebrew-core#170959

[jhendersonHDF]

Hi @chenrui333,

several versions of AppleClang have been problematic due to having the type and macros for _Float16 support while (I believe) having an issue with the version of compiler-rt used. If you're not necessarily interested in _Float16 support, it can be disabled with the configure option --disable-nonstandard-feature-float16 (Autotools) or -DHDF5_ENABLE_NONSTANDARD_FEATURE_FLOAT16=OFF (CMake). Otherwise, we can see if we can come up with a configure time check that will fully catch this on MacOS 12. I believe we were only using homebrew to install ninja on the MacOS 12 GitHub runner at the time this was tested, so there may be some differences between what was being tested.

While this particular GitHub issue dealt with compile failures in the library's main source code, it looks like your configure logs show that the library correctly picked up and built in _Float16 support without failing any of the configure checks I added, but then fails when compiling the test code. I'm not sure why that would be.