On 18/04/2018 23:55, Jack Stalnaker wrote: > Yeah, I realize it's a difficult question with no example. It would be > quite difficult to chop out a chunk of the code showing the 5x slowdown, > though, I think. I was probing for something big or obvious I may have > missed, or some known issue with the later versions, since this is so > dramatic, and since the only thing that has changed is the compiler. The > compilation options are minimal. I'm using -g -Og, and that's it. I have > tried a release build with some finer tuning, but that doesn't show much > improvement. A 5x slowdown sounds like SIMD-vs-integer code, for embarrassingly-parallel source (auto-vectorized vs scalar). Although, I think GCC is just now getting some auto-vectorization caps, and it is almost certain it did not in 4.8 o_O As Marc points out, you should test with -O2 instead of -Og Regards.
