c++: constrained variable template issues [PR98486]

This fixes some issues with constrained variable templates:

  - Constraints aren't checked when explicitly specializing a variable
    template.
  - Constraints aren't attached to a static data member template at
    parse time.
  - Constraints don't get propagated when (partially) instantiating a
    static data member template, so we need to make sure to look up
    constraints using the most general template during satisfaction.

	PR c++/98486

gcc/cp/ChangeLog:

	* constraint.cc (get_normalized_constraints_from_decl): Always
	look up constraints using the most general template.
	* decl.c (grokdeclarator): Set constraints on a static data
	member template.
	* pt.c (determine_specialization): Check constraints on a
	variable template.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-var-templ1.C: New test.
	* g++.dg/cpp2a/concepts-var-templ1a.C: New test.
	* g++.dg/cpp2a/concepts-var-templ1b.C: New test.

1 files changed, 5 insertions, 3 deletions

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 1aaf1e2..2896efd 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -918,20 +918,22 @@ get_normalized_constraints_from_decl (tree d, bool diag = false)
       tmpl = most_general_template (tmpl);
   }
 
+  d = tmpl ? tmpl : decl;
+
   /* If we're not diagnosing errors, use cached constraints, if any.  */
   if (!diag)
-    if (tree *p = hash_map_safe_get (normalized_map, tmpl))
+    if (tree *p = hash_map_safe_get (normalized_map, d))
       return *p;
 
   tree norm = NULL_TREE;
-  if (tree ci = get_constraints (decl))
+  if (tree ci = get_constraints (d))
     {
       push_access_scope_guard pas (decl);
       norm = get_normalized_constraints_from_info (ci, tmpl, diag);
     }
 
   if (!diag)
-    hash_map_safe_put<hm_ggc> (normalized_map, tmpl, norm);
+    hash_map_safe_put<hm_ggc> (normalized_map, d, norm);
 
   return norm;
 }