https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84777
Bug ID: 84777 Summary: -Os inhibits all vectorization Product: gcc Version: 8.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: linux at carewolf dot com Target Milestone: --- Neither the command-line flag -ftree-loop-vectorize nor -fopenmp combined with "#pragma omp simd" works when -Os is active. It seems that it when specified manually vectorization should be work even in -Os mode. I can almost see why -ftree-loop-vectorize wouldn't work, which is why I tried the manual marking of loops to vectorize, but the latter didn't work either. I would suggest documenting this behavior and fix at least vectorizing manually marked loops.