http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51005
Bug #: 51005 Summary: -ftree-tail-merge slows down compilation of 20001226-1.c Classification: Unclassified Product: gcc Version: 4.7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization AssignedTo: unassig...@gcc.gnu.org ReportedBy: vr...@gcc.gnu.org Reported by David Miller in http://gcc.gnu.org/ml/gcc-patches/2011-10/msg02780.html: ... My check-gcc runs are completely dominated by the time it takes to test compile.exp=20001226-1.c [...] Unfortunately, at -O2 this testcase causes exponential cost problems which are beyond my skills to fix. Specifically, tail_merge_optimize() applies it's clusters and iterate_fix_dominators() hits the worst case O(n) complexity of et_splay for a CFG structured like this. :-/ %38 of the compilation time is spent in et_splay(). ...