See http://gcc.gnu.org/ml/gcc/2005-08/msg00284.html. IMHO it's currently only working for Linux. Given the author has claimed a big performance boost with this patch, I guess it should be ported mingw32 since it's also an i386 host.
-- Summary: FTZ/DAZ for SSE should be ported to mingw32 Product: gcc Version: 4.1.1 Status: UNCONFIRMED Severity: enhancement Priority: P3 Component: target AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: zuxy dot meng at gmail dot com GCC build triplet: mingw32 GCC host triplet: mingw32 GCC target triplet: mingw32 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29498