diff options
Diffstat (limited to 'gcc/predict.c')
| -rw-r--r-- | gcc/predict.c | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/gcc/predict.c b/gcc/predict.c index 31c5565..396e150 100644 --- a/gcc/predict.c +++ b/gcc/predict.c @@ -3249,3 +3249,99 @@ report_predictor_hitrates (void) loop_optimizer_finalize (); } +/* Force edge E to be cold. + If IMPOSSIBLE is true, for edge to have count and probability 0 otherwise + keep low probability to represent possible error in a guess. This is used + i.e. in case we predict loop to likely iterate given number of times but + we are not 100% sure. + + This function locally updates profile without attempt to keep global + consistency which can not be reached in full generality without full profile + rebuild from probabilities alone. Doing so is not necessarily a good idea + because frequencies and counts may be more realistic then probabilities. + + In some cases (such as for elimination of early exits during full loop + unrolling) the caller can ensure that profile will get consistent + afterwards. */ + +void +force_edge_cold (edge e, bool impossible) +{ + gcov_type count_sum = 0; + int prob_sum = 0; + edge_iterator ei; + edge e2; + gcov_type old_count = e->count; + int old_probability = e->probability; + gcov_type gcov_scale = REG_BR_PROB_BASE; + int prob_scale = REG_BR_PROB_BASE; + + /* If edge is already improbably or cold, just return. */ + if (e->probability <= impossible ? PROB_VERY_UNLIKELY : 0 + && (!impossible || !e->count)) + return; + FOR_EACH_EDGE (e2, ei, e->src->succs) + if (e2 != e) + { + count_sum += e2->count; + prob_sum += e2->probability; + } + + /* If there are other edges out of e->src, redistribute probabilitity + there. */ + if (prob_sum) + { + e->probability + = MIN (e->probability, impossible ? 0 : PROB_VERY_UNLIKELY); + if (old_probability) + e->count = RDIV (e->count * e->probability, old_probability); + else + e->count = MIN (e->count, impossible ? 0 : 1); + + if (count_sum) + gcov_scale = RDIV ((count_sum + old_count - e->count) * REG_BR_PROB_BASE, + count_sum); + prob_scale = RDIV ((REG_BR_PROB_BASE - e->probability) * REG_BR_PROB_BASE, + prob_sum); + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Making edge %i->%i %s by redistributing " + "probability to other edges.\n", + e->src->index, e->dest->index, + impossible ? "imposisble" : "cold"); + FOR_EACH_EDGE (e2, ei, e->src->succs) + if (e2 != e) + { + e2->count = RDIV (e2->count * gcov_scale, REG_BR_PROB_BASE); + e2->probability = RDIV (e2->probability * prob_scale, + REG_BR_PROB_BASE); + } + } + /* If all edges out of e->src are unlikely, the basic block itself + is unlikely. */ + else + { + e->probability = REG_BR_PROB_BASE; + + /* If we did not adjusting, the source basic block has no likely edeges + leaving other direction. In that case force that bb cold, too. + This in general is difficult task to do, but handle special case when + BB has only one predecestor. This is common case when we are updating + after loop transforms. */ + if (!prob_sum && !count_sum && single_pred_p (e->src) + && e->src->frequency > (impossible ? 0 : 1)) + { + int old_frequency = e->src->frequency; + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Making bb %i %s.\n", e->src->index, + impossible ? "imposisble" : "cold"); + e->src->frequency = MIN (e->src->frequency, impossible ? 0 : 1); + e->src->count = e->count = RDIV (e->src->count * e->src->frequency, + old_frequency); + force_edge_cold (single_pred_edge (e->src), impossible); + } + else if (dump_file && (dump_flags & TDF_DETAILS) + && maybe_hot_bb_p (cfun, e->src)) + fprintf (dump_file, "Giving up on making bb %i %s.\n", e->src->index, + impossible ? "imposisble" : "cold"); + } +} |