http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48227
Summary: "rep ret" generated for -march=core2 Product: gcc Version: 4.5.4 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target AssignedTo: unassig...@gcc.gnu.org ReportedBy: zuxy.m...@gmail.com gcc 4.5 will use "rep; ret" for K8, Athlon, AMDFam10, Core2, and generic. Looking into the change history, we can see that gcc has padded returns for Core2 ever since Core2 support was added here: http://gcc.gnu.org/ml/gcc-patches/2006-11/msg00860.html It is suspected that Vlad just copied the generic tunings for Core2, and didn't notice that there was no particular reason to pad returns for Core2.