https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63503
--- Comment #23 from Evandro <e.menezes at samsung dot com> --- (In reply to Wilco from comment #22) > Unrolling alone isn't good enough in sum reductions. As I mentioned before, > GCC doesn't enable any of the useful loop optimizations by default. So add > -fvariable-expansion-in-unroller to get a good speedup with unrolling. Again > these are all generic GCC issues. Adding -fvariable-expansion-in-unroller when using -funroll-loops results in practically the same code being emitted.
