Profiling revealed that sat_hasher::equal accounts for nearly 40% of
compile time in some cmcstl2 tests.
This patch eliminates this bottleneck by caching the ATOMIC_CONSTRs
returned by normalize_atom. This in turn allows us to replace the
expensive atomic_constraints_identical_p check in sat_hasher::equal
with cheap pointer equality, with no loss in cache hit rate.
With this patch, compile time for the cmcstl2 test
test/algorithm/set_symmetric_difference4.cpp drops from 19s to 11s with
an --enable-checking=release compiler.
gcc/cp/ChangeLog:
* constraint.cc (atom_cache): Define this deletable hash_table.
(normalize_atom): Use it to cache ATOMIC_CONSTRs when not
generating diagnostics.
(sat_hasher::hash): Use htab_hash_pointer instead of
hash_atomic_constraint.
(sat_hasher::equal): Test for pointer equality instead of
atomic_constraints_identical_p.
* cp-tree.h (struct atom_hasher): Moved and renamed from ...
* logic.cc (struct constraint_hash): ... here.
(clause::m_set): Adjust accordingly.
---
gcc/cp/constraint.cc | 27 ++++++++++++++++++++++++---
gcc/cp/cp-tree.h | 15 +++++++++++++++
gcc/cp/logic.cc | 17 +----------------
3 files changed, 40 insertions(+), 19 deletions(-)
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index c871a8ab86a..613ced26e2b 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -710,6 +710,10 @@ normalize_concept_check (tree check, tree args, norm_info
info)
return normalize_expression (def, subst, info);
}
+/* Used by normalize_atom to cache ATOMIC_CONSTRs. */
+
+static GTY((deletable)) hash_table<atom_hasher> *atom_cache;
+
/* The normal form of an atom depends on the expression. The normal
form of a function call to a function concept is a check constraint
for that concept. The normal form of a reference to a variable
@@ -729,7 +733,19 @@ normalize_atom (tree t, tree args, norm_info info)
/* Build a new info object for the atom. */
tree ci = build_tree_list (t, info.context);
- return build1 (ATOMIC_CONSTR, ci, map);
+ tree atom = build1 (ATOMIC_CONSTR, ci, map);
+ if (!info.generate_diagnostics ())
+ {
+ /* Cache the ATOMIC_CONSTRs that we return, so that sat_hasher::equal
+ later can cheaply compare two atoms using just pointer equality. */
+ if (!atom_cache)
+ atom_cache = hash_table<atom_hasher>::create_ggc (31);
+ tree *slot = atom_cache->find_slot (atom, INSERT);
+ if (*slot)
+ return *slot;
+ *slot = atom;
+ }
+ return atom;
}
/* Returns the normal form of an expression. */
@@ -2294,13 +2310,18 @@ struct sat_hasher : ggc_ptr_hash<sat_entry>
{
static hashval_t hash (sat_entry *e)
{
- hashval_t value = hash_atomic_constraint (e->constr);
+ /* Since normalize_atom caches the ATOMIC_CONSTRs it returns,
+ we can assume pointer-based identity for fast hashing and
+ comparison. Even if this assumption is violated, that's
+ okay, we'll just get a cache miss. */
+ hashval_t value = htab_hash_pointer (e->constr);
return iterative_hash_template_arg (e->args, value);
}
static bool equal (sat_entry *e1, sat_entry *e2)
{
- if (!atomic_constraints_identical_p (e1->constr, e2->constr))
+ /* As in sat_hasher::hash. */
+ if (e1->constr != e2->constr)
return false;
return template_args_equal (e1->args, e2->args);
}
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 26852f6f2e3..eda4c56b406 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7835,6 +7835,21 @@ extern hashval_t iterative_hash_constraint (tree,
hashval_t);
extern hashval_t hash_atomic_constraint (tree);
extern void diagnose_constraints (location_t, tree, tree);
+/* A structural hasher for ATOMIC_CONSTRs. */
+
+struct atom_hasher : default_hash_traits<tree>
+{
+ static hashval_t hash (tree t)
+ {
+ return hash_atomic_constraint (t);
+ }
+
+ static bool equal (tree t1, tree t2)
+ {
+ return atomic_constraints_identical_p (t1, t2);
+ }
+};
+
/* in logic.cc */
extern bool subsumes (tree, tree);
diff --git a/gcc/cp/logic.cc b/gcc/cp/logic.cc
index 194b743192d..6701488bc1c 100644
--- a/gcc/cp/logic.cc
+++ b/gcc/cp/logic.cc
@@ -47,21 +47,6 @@ along with GCC; see the file COPYING3. If not see
#include "toplev.h"
#include "type-utils.h"
-/* Hash functions for atomic constrains. */
-
-struct constraint_hash : default_hash_traits<tree>
-{
- static hashval_t hash (tree t)
- {
- return hash_atomic_constraint (t);
- }
-
- static bool equal (tree t1, tree t2)
- {
- return atomic_constraints_identical_p (t1, t2);
- }
-};
-
/* A conjunctive or disjunctive clause.
Each clause maintains an iterator that refers to the current
@@ -219,7 +204,7 @@ struct clause
}
std::list<tree> m_terms; /* The list of terms. */
- hash_set<tree, false, constraint_hash> m_set; /* The set of atomic
constraints. */
+ hash_set<tree, false, atom_hasher> m_set; /* The set of atomic constraints.
*/
iterator m_current; /* The current term. */
};
--
2.29.2.154.g7f7ebe054a
