https://gcc.gnu.org/g:4ba4165d66b18d7c5b8af02ecdf38bfa0690c106
commit r15-4017-g4ba4165d66b18d7c5b8af02ecdf38bfa0690c106
Author: Richard Biener <rguent...@suse.de>
Date: Thu Sep 26 11:43:21 2024 +0200
tree-optimiztation/114855 - profile prediction slowness
The testcase in PR114855 shows profile prediction to evaluate
the same SSA def via expr_expected_value for each condition or
switch in a function. The following patch caches the expected
value (and probability/predictor) for each visited SSA def,
also protecting against recursion and thus obsoleting the visited
bitmap. This reduces the time spent in branch prediction from
1.2s to 0.3s, though callgrind which was how I noticed this
seems to be comparatively very much happier about the change than
this number suggests.
PR tree-optimization/114855
* predict.cc (ssa_expected_value): New global.
(expr_expected_value): Do not take bitmap.
(expr_expected_value_1): Likewise. Use ssa_expected_value
to cache results for a SSA def.
(tree_predict_by_opcode): Adjust.
(tree_estimate_probability): Manage ssa_expected_value.
(tree_guess_outgoing_edge_probabilities): Likewise.
Diff:
---
gcc/predict.cc | 117 ++++++++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 91 insertions(+), 26 deletions(-)
diff --git a/gcc/predict.cc b/gcc/predict.cc
index f611161f4aa0..affa037371ca 100644
--- a/gcc/predict.cc
+++ b/gcc/predict.cc
@@ -517,6 +517,16 @@ struct edge_prediction {
static hash_map<const_basic_block, edge_prediction *> *bb_predictions;
+/* Global cache for expr_expected_value. */
+
+struct expected_value
+{
+ tree val;
+ enum br_predictor predictor;
+ HOST_WIDE_INT probability;
+};
+static hash_map<int_hash<unsigned, 0>, expected_value> *ssa_expected_value;
+
/* Return true if the one of outgoing edges is already predicted by
PREDICTOR. */
@@ -2356,14 +2366,14 @@ guess_outgoing_edge_probabilities (basic_block bb)
combine_predictions_for_insn (BB_END (bb), bb);
}
-static tree expr_expected_value (tree, bitmap, enum br_predictor *predictor,
+static tree expr_expected_value (tree, enum br_predictor *predictor,
HOST_WIDE_INT *probability);
/* Helper function for expr_expected_value. */
static tree
expr_expected_value_1 (tree type, tree op0, enum tree_code code,
- tree op1, bitmap visited, enum br_predictor *predictor,
+ tree op1, enum br_predictor *predictor,
HOST_WIDE_INT *probability)
{
gimple *def;
@@ -2401,8 +2411,19 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
def = SSA_NAME_DEF_STMT (op0);
/* If we were already here, break the infinite cycle. */
- if (!bitmap_set_bit (visited, SSA_NAME_VERSION (op0)))
- return NULL;
+ bool existed_p;
+ expected_value *res
+ = &ssa_expected_value->get_or_insert (SSA_NAME_VERSION (op0),
+ &existed_p);
+ if (existed_p)
+ {
+ *probability = res->probability;
+ *predictor = res->predictor;
+ return res->val;
+ }
+ res->val = NULL_TREE;
+ res->predictor = *predictor;
+ res->probability = *probability;
if (gphi *phi = dyn_cast <gphi *> (def))
{
@@ -2443,7 +2464,7 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
continue;
}
HOST_WIDE_INT probability2;
- tree new_val = expr_expected_value (arg, visited, &predictor2,
+ tree new_val = expr_expected_value (arg, &predictor2,
&probability2);
/* If we know nothing about value, give up. */
if (!new_val)
@@ -2477,6 +2498,11 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
*predictor = PRED_COMBINED_VALUE_PREDICTIONS_PHI;
*probability = MIN (p1, p2);
}
+
+ res = ssa_expected_value->get (SSA_NAME_VERSION (op0));
+ res->val = val;
+ res->predictor = *predictor;
+ res->probability = *probability;
return val;
}
if (is_gimple_assign (def))
@@ -2484,11 +2510,19 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
if (gimple_assign_lhs (def) != op0)
return NULL;
- return expr_expected_value_1 (TREE_TYPE (gimple_assign_lhs (def)),
- gimple_assign_rhs1 (def),
- gimple_assign_rhs_code (def),
- gimple_assign_rhs2 (def),
- visited, predictor, probability);
+ tree val = expr_expected_value_1 (TREE_TYPE (gimple_assign_lhs (def)),
+ gimple_assign_rhs1 (def),
+ gimple_assign_rhs_code (def),
+ gimple_assign_rhs2 (def),
+ predictor, probability);
+ if (val)
+ {
+ res = ssa_expected_value->get (SSA_NAME_VERSION (op0));
+ res->val = val;
+ res->predictor = *predictor;
+ res->probability = *probability;
+ }
+ return val;
}
if (is_gimple_call (def))
@@ -2511,7 +2545,11 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
if (*predictor == PRED_BUILTIN_EXPECT)
*probability
= HITRATE (param_builtin_expect_probability);
- return gimple_call_arg (def, 1);
+ val = gimple_call_arg (def, 1);
+ res->val = val;
+ res->predictor = *predictor;
+ res->probability = *probability;
+ return val;
}
return NULL;
}
@@ -2524,7 +2562,11 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
to value ranges. This makes predictor to assume that
malloc always returns (size_t)1 which is not the same
as returning non-NULL. */
- return fold_convert (type, boolean_true_node);
+ tree val = fold_convert (type, boolean_true_node);
+ res->val = val;
+ res->predictor = *predictor;
+ res->probability = *probability;
+ return val;
}
if (DECL_BUILT_IN_CLASS (decl) == BUILT_IN_NORMAL)
@@ -2541,7 +2583,11 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
*predictor = PRED_BUILTIN_EXPECT;
*probability
= HITRATE (param_builtin_expect_probability);
- return gimple_call_arg (def, 1);
+ val = gimple_call_arg (def, 1);
+ res->val = val;
+ res->predictor = *predictor;
+ res->probability = *probability;
+ return val;
}
case BUILT_IN_EXPECT_WITH_PROBABILITY:
{
@@ -2550,7 +2596,12 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
return NULL;
val = gimple_call_arg (def, 0);
if (TREE_CONSTANT (val))
- return val;
+ {
+ res->val = val;
+ res->predictor = *predictor;
+ res->probability = *probability;
+ return val;
+ }
/* Compute final probability as:
probability * REG_BR_PROB_BASE. */
tree prob = gimple_call_arg (def, 2);
@@ -2579,7 +2630,11 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
"probability %qE is outside "
"the range [0.0, 1.0]", prob);
- return gimple_call_arg (def, 1);
+ val = gimple_call_arg (def, 1);
+ res->val = val;
+ res->predictor = *predictor;
+ res->probability = *probability;
+ return val;
}
case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_N:
@@ -2598,6 +2653,9 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
/* Assume that any given atomic operation has low contention,
and thus the compare-and-swap operation succeeds. */
*predictor = PRED_COMPARE_AND_SWAP;
+ res->val = boolean_true_node;
+ res->predictor = *predictor;
+ res->probability = *probability;
return boolean_true_node;
case BUILT_IN_REALLOC:
case BUILT_IN_GOMP_REALLOC:
@@ -2605,7 +2663,10 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
*predictor = PRED_MALLOC_NONNULL;
/* FIXME: This is wrong and we need to convert the logic
to value ranges. */
- return fold_convert (type, boolean_true_node);
+ res->val = fold_convert (type, boolean_true_node);
+ res->predictor = *predictor;
+ res->probability = *probability;
+ return res->val;
default:
break;
}
@@ -2626,7 +2687,7 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
if (TREE_CODE (op0) != INTEGER_CST)
{
/* See if expected value of op0 is good enough to determine the
result. */
- nop0 = expr_expected_value (op0, visited, predictor, probability);
+ nop0 = expr_expected_value (op0, predictor, probability);
if (nop0
&& (res = fold_build2 (code, type, nop0, op1)) != NULL
&& TREE_CODE (res) == INTEGER_CST)
@@ -2645,7 +2706,7 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
if (TREE_CODE (op1) != INTEGER_CST)
{
/* See if expected value of op1 is good enough to determine the
result. */
- nop1 = expr_expected_value (op1, visited, &predictor2, &probability2);
+ nop1 = expr_expected_value (op1, &predictor2, &probability2);
if (nop1
&& (res = fold_build2 (code, type, op0, nop1)) != NULL
&& TREE_CODE (res) == INTEGER_CST)
@@ -2700,7 +2761,7 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
if (get_gimple_rhs_class (code) == GIMPLE_UNARY_RHS)
{
tree res;
- op0 = expr_expected_value (op0, visited, predictor, probability);
+ op0 = expr_expected_value (op0, predictor, probability);
if (!op0)
return NULL;
res = fold_build1 (code, type, op0);
@@ -2720,8 +2781,7 @@ expr_expected_value_1 (tree type, tree op0, enum
tree_code code,
implementation. */
static tree
-expr_expected_value (tree expr, bitmap visited,
- enum br_predictor *predictor,
+expr_expected_value (tree expr, enum br_predictor *predictor,
HOST_WIDE_INT *probability)
{
enum tree_code code;
@@ -2736,8 +2796,7 @@ expr_expected_value (tree expr, bitmap visited,
extract_ops_from_tree (expr, &code, &op0, &op1);
return expr_expected_value_1 (TREE_TYPE (expr),
- op0, code, op1, visited, predictor,
- probability);
+ op0, code, op1, predictor, probability);
}
@@ -2781,8 +2840,7 @@ tree_predict_by_opcode (basic_block bb)
if (gswitch *sw = dyn_cast <gswitch *> (stmt))
{
tree index = gimple_switch_index (sw);
- tree val = expr_expected_value (index, auto_bitmap (),
- &predictor, &probability);
+ tree val = expr_expected_value (index, &predictor, &probability);
if (val && TREE_CODE (val) == INTEGER_CST)
{
edge e = find_taken_edge_switch_expr (sw, val);
@@ -2807,7 +2865,7 @@ tree_predict_by_opcode (basic_block bb)
op1 = gimple_cond_rhs (stmt);
cmp = gimple_cond_code (stmt);
type = TREE_TYPE (op0);
- val = expr_expected_value_1 (boolean_type_node, op0, cmp, op1, auto_bitmap
(),
+ val = expr_expected_value_1 (boolean_type_node, op0, cmp, op1,
&predictor, &probability);
if (val && TREE_CODE (val) == INTEGER_CST)
{
@@ -3215,6 +3273,8 @@ tree_estimate_probability (bool dry_run)
determine_unlikely_bbs ();
bb_predictions = new hash_map<const_basic_block, edge_prediction *>;
+ ssa_expected_value = new hash_map<int_hash<unsigned, 0>, expected_value>;
+
tree_bb_level_predictions ();
record_loop_exits ();
@@ -3232,6 +3292,8 @@ tree_estimate_probability (bool dry_run)
delete bb_predictions;
bb_predictions = NULL;
+ delete ssa_expected_value;
+ ssa_expected_value = NULL;
if (!dry_run
&& profile_status_for_fn (cfun) != PROFILE_READ)
@@ -3245,12 +3307,15 @@ void
tree_guess_outgoing_edge_probabilities (basic_block bb)
{
bb_predictions = new hash_map<const_basic_block, edge_prediction *>;
+ ssa_expected_value = new hash_map<int_hash<unsigned, 0>, expected_value>;
tree_estimate_probability_bb (bb, true);
combine_predictions_for_bb (bb, false);
if (flag_checking)
bb_predictions->traverse<void *, assert_is_empty> (NULL);
delete bb_predictions;
bb_predictions = NULL;
+ delete ssa_expected_value;
+ ssa_expected_value = NULL;
}
/* Filter function predicate that returns true for a edge predicate P
