I noticed a big performance regression with zdoom compiled with GCC 6 in release mode. When I load Ancient Aliens map29, just the starting area is so slow that each frame is separated by around 1 sec and half, while with GCC 5 and less the frame rate is more or less 15 fps. It's even slower than debug mode.
I hope somebody can help with the real issue (could be a compiler regression, indeed!). Using Ubuntu 16.04 x86_64.