The codegen differences introduced by free_alng_data can be promptly exposed using -fcompare-debug=-g0.
Two such errors are known to me, on x86_64-linux-gnu native bootstrap: ada/einfo.adb fails -fcompare-debug=-g0 because boolean_type_node is modified. http://gcc.gnu.org/ml/gcc-patches/2009-11/msg00414.html has details. tree.c fails -fcompare-debug=-g0 because declaration UIDs go out of sync when local declarations of types are removed in free_lang_data_in_block(). http://gcc.gnu.org/ml/gcc-patches/2009-11/msg00457.html has details. -- Summary: flag_gtoggle in free_lang_data hides -fcompare-debug errors Product: gcc Version: 4.5.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: lto AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: aoliva at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42088