We should renable the this flag at least at -O3 and above. See PR 15023 for why it was disabled, every problem except for the compiler time issue was a latent target bug.
-- Summary: [4.0/4.1 Regression] flag_rename_registers is not enabled at -O3 or above Product: gcc Version: 4.0.1 Status: UNCONFIRMED Severity: normal Priority: P2 Component: rtl-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: pinskia at gcc dot gnu dot org CC: gcc-bugs at gcc dot gnu dot org BugsThisDependsOn: 15023 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22208