c++: Hash placeholder constraint in ctp_hasher

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.

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 5472cc51b8ad9b465f64a8fdc5a2b2d668e334c9..afd5435cc3ed93f329719b09f2039040bf843f43 100644 (file)
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -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);

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index c6f102564ce0d6230e50dd9e0169e4b6cc3e74d1..609d8941cf72ffbe1397b0b390cc188102635dee 100644 (file)
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -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);

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 057797f213f5529656a49845826de9925b4dbe5f..108e929b8ee6cd9348c0699f0a028a3cf2c90540 100644 (file)
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -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);