GCC 4.5.2 at the SAT Competition’13

(Note update below)

Just a short note. All MiniSat-derived SAT solvers might give wrong results during the competition. No, MiniSat doesn’t have a bug. GCC has a giant bug. Vegard reported this years ago — I personally put about 12h tracking it down, posted it to the CryptoMiniSat mailing list, and Vegard took it up, stripped it down and reported it.

This is a well-known bug, there is a thread about it on the MiniSat mailing list and I personally asked the competition organizers back in 2011 not to use the 4.5.2(or .3?) they wanted to use. I used to have code to check for this bug (there is a handy check attached to the bug report), but I removed it, though maybe I should add it back. It’s fixed in 4.5.4+, still present in 4.5.3 where Vegard&me found it. I hope I will be able to convince the organisers this time around, too :) By the way, the option you need to pass to gcc to avoid the bug is “-fno-tree-pre” — though of course this turns off an optimisation and so slows down the final executable.

Update: The organisers decided to move to gcc 4.8.0. This is very good news. They also note that the speed of the solvers is better, which is also very good news. I am happy I contributed to this welcome improvement and I hope it doesn’t cause any delays or inconveniences to anyone.