If you use -O2 -ftree-vectorize -msse5 (or now -O3 -msse5), the compiler generates an insn not found message, because there is a typo in i386.c.
-- Summary: SSE5 vectorized SI->DI conversions broken Product: gcc Version: 4.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: michael dot meissner at amd dot com GCC build triplet: x86_64-pc-gnu-linux GCC host triplet: x86_64-pc-gnu-linux GCC target triplet: x86_64-pc-gnu-linux http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33524