Hi.
This patch is a reaction to Jason's commit where he introduced new C++
attributes.
First I would like to align cold/hot to __builtin_expect, so I adjusted
probability
and made the predictors first match predictors.
Second I fixed how we consider the predictors in switch statements, so that
we can correctly predict situation in predict-3.
Honza is fine with the patch, I'll install it later if there are no objections.
Survives tests and bootstrap on xc86_64-linux-gnu.
Martin
gcc/ChangeLog:
2018-11-29 Martin Liska
* predict.c (set_even_probabilities): Include also
unlikely_count in calculation.
(combine_predictions_for_bb): Consider also HOT and
COLD labels predictions.
* predict.def (PRED_HOT_LABEL): Move it just after
__builtin_expect_with_probability predictor.
(PRED_COLD_LABEL): Likewise.
gcc/testsuite/ChangeLog:
2018-11-29 Martin Liska
* g++.dg/predict-2.C: New test.
* g++.dg/predict-3.C: New test.
* g++.dg/predict-4.C: New test.
* gcc.dg/tree-ssa/attr-hotcold-2.c: Adjust test-case.
---
gcc/predict.c | 15 ---
gcc/predict.def| 15 ---
gcc/testsuite/g++.dg/predict-2.C | 16
gcc/testsuite/g++.dg/predict-3.C | 17 +
gcc/testsuite/g++.dg/predict-4.C | 17 +
gcc/testsuite/gcc.dg/tree-ssa/attr-hotcold-2.c | 4 ++--
6 files changed, 72 insertions(+), 12 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/predict-2.C
create mode 100644 gcc/testsuite/g++.dg/predict-3.C
create mode 100644 gcc/testsuite/g++.dg/predict-4.C
diff --git a/gcc/predict.c b/gcc/predict.c
index 5ad252c2d39..81dbb67da4e 100644
--- a/gcc/predict.c
+++ b/gcc/predict.c
@@ -878,11 +878,18 @@ set_even_probabilities (basic_block bb,
profile_probability prob
= profile_probability::from_reg_br_prob_base (p);
profile_probability remainder = prob.invert ();
+ remainder -= profile_probability::very_unlikely ()
+ .apply_scale (unlikely_count, 1);
+ int count = nedges - unlikely_count - 1;
+ gcc_assert (count >= 0);
+ profile_probability even = remainder.apply_scale (1, count);
if (prediction->ep_edge == e)
e->probability = prob;
+ else if (unlikely_edges != NULL && unlikely_edges->contains (e))
+ e->probability = profile_probability::very_unlikely ();
else
- e->probability = remainder.apply_scale (1, nedges - 1);
+ e->probability = even;
}
else
e->probability = profile_probability::never ();
@@ -1217,10 +1224,12 @@ combine_predictions_for_bb (basic_block bb, bool dry_run)
if (preds)
for (pred = *preds; pred; pred = pred->ep_next)
{
- if (pred->ep_probability <= PROB_VERY_UNLIKELY)
+ if (pred->ep_probability <= PROB_VERY_UNLIKELY
+ || pred->ep_predictor == PRED_COLD_LABEL)
unlikely_edges.add (pred->ep_edge);
if (pred->ep_probability >= PROB_VERY_LIKELY
- || pred->ep_predictor == PRED_BUILTIN_EXPECT)
+ || pred->ep_predictor == PRED_BUILTIN_EXPECT
+ || pred->ep_predictor == PRED_HOT_LABEL)
likely_edges.add (pred);
}
diff --git a/gcc/predict.def b/gcc/predict.def
index e2a56f95955..27d0e4dc6f9 100644
--- a/gcc/predict.def
+++ b/gcc/predict.def
@@ -78,6 +78,14 @@ DEF_PREDICTOR (PRED_BUILTIN_EXPECT_WITH_PROBABILITY,
"__builtin_expect_with_probability", PROB_UNINITIALIZED,
PRED_FLAG_FIRST_MATCH)
+/* Branches to hot labels are likely. */
+DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (90),
+ PRED_FLAG_FIRST_MATCH)
+
+/* Branches to cold labels are extremely unlikely. */
+DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", HITRATE (90),
+ PRED_FLAG_FIRST_MATCH)
+
/* Use number of loop iterations guessed by the contents of the loop. */
DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations",
PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH)
@@ -171,13 +179,6 @@ DEF_PREDICTOR (PRED_LOOP_GUARD, "loop guard", HITRATE (73), 0)
DEF_PREDICTOR (PRED_LOOP_GUARD_WITH_RECURSION, "loop guard with recursion",
HITRATE (85), 0)
-/* Branches to hot labels are likely. */
-DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (85), 0)
-
-/* Branches to cold labels are extremely unlikely. */
-DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", PROB_VERY_LIKELY,
- PRED_FLAG_FIRST_MATCH)
-
/* The following predictors are used in Fortran. */
/* Branch leading to an integer overflow are extremely unlikely. */
diff --git a/gcc/testsuite/g++.dg/predict-2.C b/gcc/testsuite/g++.dg/predict-2.C
new file mode 100644
index 000..1e0ac1d2c48
--- /dev/null
+++ b/gcc/testsuite/g++.dg/predict-2.C
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-profile_estimate -std=c++11" } */
+
+int a, b, c;
+
+void
+bar()
+{
+ if (a == 123)
+[[likely]] c = 5;
