Got Gromacs 4.5.4 compiled without -ipa (-march=auto -O3 -OPT:Ofast -fno-math-errno -ffast-math). I was hoping that the conclusions will be straightforward, but they're not:
- some parts of the code get up to 15% speedup;
- in other parts of the code there's a horrible slowdown, up to 2.5x;
- I get occasional segfaults.