When using all O3 flags without -ftree-vectorize, all work good. So, I think there is a trouble which can be determined by testing this option on sys-libs/zlib - package.
-- Summary: -ftree-vectorize and zlib: firefox crashes with segmentation faults on start Product: gcc Version: 4.4.2 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: mecareful at gmail dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42513