[Gretl-devel] gretl AVX issue

Dear Dirk and Johannes, I'm appealing to you as the packagers who have shown the greatest interest in gretl over the years. I think you both know about the "gretl AVX" issue, but then I'm sure you have lots of things to think about so let me briefly restate it, as a lead-up to asking your opinion. Since version 1.9.14 of November 2013, gretl's configure script has by default checked the build host for support for the SSE2 and AVX instruction sets, and has enabled these instructions if they're supported. However, there are configure switches available to disable each: --disable-sse2 --disable-avx The current default is fine for individuals building gretl for their own use, but not necessarily fine for packagers. SSE2 is not much of a issue, I think -- it has been in Intel CPUs since 2001 and AMD CPUs since 2003. AVX, on the other hand, can be a problem. It has been in new Intel CPUs since Q1 of 2011 and AMD CPUs since Q3 of 2011, so there are still plenty of PCs out there that don't support AVX. So here's the key point: If you build gretl on an AVX host without using the --disable-avx flag with configure, you'll get a binary that will not run on a non-AVX machine (it will crash with "Illegal instruction" on start-up). And we're seeing this happen in userland. How do you think we should handle this? Do you reckon we should revise our configure script to enable AVX only if it's explicitly requested? Or is it enough if packagers are aware on the issue? One more question: since we're getting nasty reports from people with non-AVX machines on both Debian-derived distros and Fedora, we need to do something about it soon. How would you feel about making available new non-AVX builds of recent gretl? (It seems that packagers sometimes put out a second build of given sources, though I don't know the usual criteria for doing that.) Allin