------- Comment #2 from xinliangli at gmail dot com 2008-02-25 21:36 ------- (In reply to comment #1) > (In reply to comment #0) > > It is beneficial to unroll reduction loop (and split the reduction target) > > to > > reduce dependence height due to recurrence, but GCC does not perform such > > optimization (-O3 -fno-tree-vectorize) > > it does, if you use -fvariable-expansion-in-unroller -funroll-loops > (this splits the reduction target into 2 accumulators. For more agressive > spiltting you can use --param max-variable-expansions-in-unrolle=[n]) >
Thanks, it is good to know the option. It would be good to tune the default behavior of the optimizer so that better out of box performance can be achieved. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35343
