http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49795
--- Comment #3 from vincenzo Innocente <vincenzo.innocente at cern dot ch> 2011-07-20 12:32:21 UTC --- my actual code looks more like this void loop() { for (int i=0; i!=N; ++i) { d[i]=a[i]+b[i]; if (c[i]<0) d[i] = -d[i]; } } where d[i] IS written unconditionally (and does not vectorize either)