Hi, force_edge_cold can be more aggressive about propagating zero counts. Honza
Bootstrapped/regtested x86_64-linux, will commit it later today. * predict.c (force_edge_cold): Handle declaring edges impossible more aggresively. Index: predict.c =================================================================== --- predict.c (revision 249244) +++ predict.c (working copy) @@ -3968,6 +3968,7 @@ force_edge_cold (edge e, bool impossible profile_count old_count = e->count; int old_probability = e->probability; int prob_scale = REG_BR_PROB_BASE; + bool uninitialized_exit = false; /* If edge is already improbably or cold, just return. */ if (e->probability <= (impossible ? PROB_VERY_UNLIKELY : 0) @@ -3978,6 +3979,8 @@ force_edge_cold (edge e, bool impossible { if (e2->count.initialized_p ()) count_sum += e2->count; + else + uninitialized_exit = true; prob_sum += e2->probability; } @@ -3989,7 +3992,7 @@ force_edge_cold (edge e, bool impossible = MIN (e->probability, impossible ? 0 : PROB_VERY_UNLIKELY); if (impossible) e->count = profile_count::zero (); - if (old_probability) + else if (old_probability) e->count = e->count.apply_scale (e->probability, old_probability); else e->count = e->count.apply_scale (1, REG_BR_PROB_BASE); @@ -4016,6 +4019,34 @@ force_edge_cold (edge e, bool impossible else { e->probability = REG_BR_PROB_BASE; + if (e->src->count == profile_count::zero ()) + return; + if (count_sum == profile_count::zero () && !uninitialized_exit + && impossible) + { + bool found = false; + for (gimple_stmt_iterator gsi = gsi_start_bb (e->src); + !gsi_end_p (gsi); gsi_next (&gsi)) + { + if (stmt_can_terminate_bb_p (gsi_stmt (gsi))) + { + found = true; + break; + } + } + if (!found) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, + "Making bb %i impossible and dropping count to 0.\n", + e->src->index); + e->count = profile_count::zero (); + e->src->count = profile_count::zero (); + FOR_EACH_EDGE (e2, ei, e->src->preds) + force_edge_cold (e2, impossible); + return; + } + } /* If we did not adjusting, the source basic block has no likely edeges leaving other direction. In that case force that bb cold, too.