Without aliasing information some passes and cleanups cannot be scheduled early. See http://gcc.gnu.org/ml/gcc-patches/2007-02/msg01176.html
-- Summary: Need to run may-alias early in IPA Product: gcc Version: 4.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization AssignedTo: dnovillo at gcc dot gnu dot org ReportedBy: dnovillo at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30791