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c++: Hash placeholder constraint in ctp_hasher

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This patch addresses a difference between the hash function and the equality
function for canonical types of template parameters (ctp_hasher). The equality
function uses comptypes (typeck.cc) (with COMPARE_STRUCTURAL) and checks
constraint equality for two auto nodes (typeck.cc:1586), while the hash
function ignores it (pt.cc:4528). This leads to hash collisions that can be
avoided by using `hash_placeholder_constraint` (constraint.cc:1150).

Note that due to the proper handling of hash collisions (hash-table.h:1059),
there is no test case that can distinguish the current implementation from the
proposed one.

	* constraint.cc (hash_placeholder_constraint): Rename to
	iterative_hash_placeholder_constraint.
	(iterative_hash_placeholder_constraint): Rename from
	hash_placeholder_constraint and add the initial val argument.
	* cp-tree.h (hash_placeholder_constraint): Rename to
	iterative_hash_placeholder_constraint.
	(iterative_hash_placeholder_constraint): Renamed from
	hash_placeholder_constraint and add the initial val argument.
	* pt.cc (struct ctp_hasher): Updated to use
	iterative_hash_placeholder_constraint in the case of a valid placeholder
	constraint.
	(auto_hash::hash): Reflect the renaming of hash_placeholder_constraint to
	iterative_hash_placeholder_constraint.
This commit is contained in:
Seyed Sajad Kahani 2024-07-18 16:01:32 +01:00 committed by Jason Merrill
parent 02cc849474
commit 0f8261eae0
3 changed files with 10 additions and 5 deletions
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4
gcc/cp/constraint.cc
View File

@ -1689,13 +1689,13 @@ equivalent_placeholder_constraints (tree c1, tree c2)
/* Return a hash value for the placeholder ATOMIC_CONSTR C. */
hashval_t
hash_placeholder_constraint (tree c)
iterative_hash_placeholder_constraint (tree c, hashval_t val)
{
tree t, a;
placeholder_extract_concept_and_args (c, t, a);
/* Like hash_tmpl_and_args, but skip the first argument. */
hashval_t val = iterative_hash_object (DECL_UID (t), 0);
val = iterative_hash_object (DECL_UID (t), val);
for (int i = TREE_VEC_LENGTH (a)-1; i > 0; --i)
val = iterative_hash_template_arg (TREE_VEC_ELT (a, i), val);

2
gcc/cp/cp-tree.h
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@ -8581,7 +8581,7 @@ extern tree_pair finish_type_constraints (tree, tree, tsubst_flags_t);
extern tree build_constrained_parameter (tree, tree, tree = NULL_TREE);
extern void placeholder_extract_concept_and_args (tree, tree&, tree&);
extern bool equivalent_placeholder_constraints (tree, tree);
extern hashval_t hash_placeholder_constraint (tree);
extern hashval_t iterative_hash_placeholder_constraint (tree, hashval_t);
extern bool deduce_constrained_parameter (tree, tree&, tree&);
extern tree resolve_constraint_check (tree);
extern tree check_function_concept (tree);

9
gcc/cp/pt.cc
View File

@ -4500,7 +4500,12 @@ struct ctp_hasher : ggc_ptr_hash<tree_node>
val = iterative_hash_object (TEMPLATE_TYPE_LEVEL (t), val);
val = iterative_hash_object (TEMPLATE_TYPE_IDX (t), val);
if (TREE_CODE (t) == TEMPLATE_TYPE_PARM)
val = iterative_hash_template_arg (CLASS_PLACEHOLDER_TEMPLATE (t), val);
{
val
= iterative_hash_template_arg (CLASS_PLACEHOLDER_TEMPLATE (t), val);
if (tree c = NON_ERROR (PLACEHOLDER_TYPE_CONSTRAINTS (t)))
val = iterative_hash_placeholder_constraint (c, val);
}
if (TREE_CODE (t) == BOUND_TEMPLATE_TEMPLATE_PARM)
val = iterative_hash_template_arg (TYPE_TI_ARGS (t), val);
--comparing_specializations;
@ -29581,7 +29586,7 @@ auto_hash::hash (tree t)
if (tree c = NON_ERROR (PLACEHOLDER_TYPE_CONSTRAINTS (t)))
/* Matching constrained-type-specifiers denote the same template
parameter, so hash the constraint. */
return hash_placeholder_constraint (c);
return iterative_hash_placeholder_constraint (c, 0);
else
/* But unconstrained autos are all separate, so just hash the pointer. */
return iterative_hash_object (t, 0);