http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51766
Bug #: 51766 Summary: [4.7 regression] sync_fetch_and_xxx atomicity Classification: Unclassified Product: gcc Version: 4.7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end AssignedTo: unassig...@gcc.gnu.org ReportedBy: d...@gcc.gnu.org During the C++11 memory model conversion, expand_builtin_sync_operation was updated. __sync_fetch_and_xxx and __sync_xxx_and_fetch now invoke expand_atomic_fetch_op with MEMMODEL_SEQUENTIAL_CST. return expand_atomic_fetch_op (target, mem, val, code, MEMMODEL_SEQ_CST, after); This has changed the memory model semantics of the builtins and causes the rs6000/POWER architecture to emit a heavy-weight "sync" instruction instead of a light-weight "lwsync" instruction, which is a regression.