> Yes, atlas has a bunch of compiler variants. I would love for most or all of 
> them to go away. But part of atlas needs fortran so it needs to deal with 
> that at least. And I believe Vince argued that for atlas and other 
> performance-critical scientific software it is beneficial to be able to try 
> different compilers to get the absolute best performance. I'm not sure who 
> actually has time to do that however. Also, atlas already builds itself 
> multiple times with different compiler options to get best performance, which 
> is why building atlas takes so long.

This is mainly historical now. Clang has gone a long way from what it was two 
years ago and can now outperform GCC on most kernels. But modern clang versions 
are not available on all platforms (10.5 PPC). Besides, fortran is still 
required for Atlas as long as you decide to build the  BLAS/LAPACK interface, 
which almost all other ports depend on. The idea of keeping multiple gcc 
variants was to avoid  the installation of a fresh copy of GCC in case the 
version the user had installed and the one Atlas required weren't the same, 
knowing that the version number is nowhere near to be important as long as the 
fortran compiler is available (it's just to build the API).

I just wish llvm had a fortran front-end to avoid this mess. And, needless to 
say, I'll welcome any suggestion to improve the layout of the port.

Vincent


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