Changing default compiler for Atlas from gcc47 to clang-3.3 on AVX capable machines

[Vincent Habchi]

Folks,

as you may know, I am conducting a major overhaul of the Atlas port. And, as part of the preliminary tests, I am happy to disclose that clang-mp-3.3 (3/2013) compiles Atlas with AVX support and, given the proper optimization flags (e.g. -fvectorize -fslp-vectorize) seems to achieve on par or better performance than the reference GCC implementation. This means that happy owners of AVX machines will be – eventually – able to break from the GCC hegemony and almost double the performance of their x86_64 implementation.

Since no gcc version on MacOS will ever be able to compile AVX assembly or generate AVX code, I was thinking about:

- Either warning owners of AVX machines that they should use clang-mp-3.3 to squeeze the most of their CPU;
- Or making clang-mp-3.3 the default compiler for those computers.

What is your opinion?

Vincent