[tblis] stochastic TBLIS/BLIS build failures

[evaleev]

stochastic failures
https://github.com/TAPPorg/reference-implementation/actions/runs/21034404114/job/60478289558#step:10:64
https://github.com/TAPPorg/reference-implementation/actions/runs/21034404114/job/60481589441#step:10:64
and subsequent successes (upon simple rerun)
https://github.com/TAPPorg/reference-implementation/actions/runs/21034404114/job/60483956098#step:10:81

seems to be due to BLIS' make/autotools(?)-based build happening inside TBLIS CMake harness. Maybe timestamp corruption? @devinamatthews any ideas? Does BLIS have a CMake harness?

P.S. interestingly, the successful build builds blis after tblis sources and produces different messages
https://github.com/TAPPorg/reference-implementation/actions/runs/21034404114/job/60483956098#step:10:91
this is likely unexpressed dependencies issue in BLIS or (less likely) TBLIS, perhaps can be worked around by disabling parallel build?

[chillenb]

This error looks like BLIS configure isn’t detecting the compiler vendor. Somehow this only causes the build to fail when the runner is skx (not zen3). For the same reason, there are also warnings about pragma omp simd because the -fopenmp-simd flag was not passed.

I think it can be fixed by adding CC=/usr/bin/gcc-14 to the CI, like here:
https://github.com/chillenb/reference-implementation/blob/b0022a3e3fa5688aca3fc8499e3b89f95ad74e47/.github/workflows/cmake.yml

[evaleev]

@chillenb thanks for the tip. It seems the problem then is that tblis's CMake harness should "forward" CMake variables like CMAKE_C_COMPILER to BLIS build harness somehow. Needing to set CC env var globally is unexpected.

[chillenb]

After some digging, I found that:

• CMake and BLIS's configure are both seeing the same C compiler; they're both /usr/bin/cc.
• BLIS configure detects the C compiler version by running $CC --version
• On Ubuntu 24.04, /usr/bin/cc --version prints: cc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
• This version string does not contain "gcc", so BLIS configure thinks it's not GCC
• ... leading to compilation failure on skx runners

The reason that setting CC=/usr/bin/gcc-14 works: it contains "gcc" as a substring.

tblis's CMAKE harness should, in principle, be passing CMAKE_C_COMPILER to BLIS more explicitly. This accidentally works right now thanks to the old behavior of CMP0132, which sets the environment variable CC on first configure.

More importantly, the compiler vendor detection in BLIS's configure script should be fixed!

[devinamatthews]

Yes if there is a better suggestion for something to grep for in the cc case please raise an issue (or PR) for blis.