c++: normalizing ttp constraints [PR115656]

Here we normalize the constraint same_as<T, bool> for the first
time during ttp coercion of B / UU, specifically constraint subsumption
checking.  During this normalization the set of in-scope template
parameters i.e. current_template_parms is empty, which we rely on
during normalization of the ttp constraints since we pass in_decl=NULL_TREE
to norm_info.  And this tricks the satisfaction cache into thinking that
the satisfaction value of same_as<T, bool> is independent of its template
parameters, and we incorrectly conflate the satisfaction value with
T = bool vs T = long and accept the specialization A<long, B>.

Since is_compatible_template_arg rewrites the ttp's constraints to
be in terms of the argument template's parameters, and since it's
the only caller of weakly_subsumes, the latter funcion can instead
pass in_decl=tmpl to avoid relying on current_template_parms.  This
patch implements this, and in turns renames weakly_subsumes to
ttp_subsumes to reflect that this predicate is now hardcoded for this
one caller.

	PR c++/115656

gcc/cp/ChangeLog:

	* constraint.cc (weakly_subsumes): Pass in_decl=tmpl to
	get_normalized_constraints_from_info.  Rename to ...
	(ttp_subsumes): ... this.
	* cp-tree.h (weakly_subsumes): Rename to ...
	(ttp_subsumes): ... this.
	* pt.cc (is_compatible_template_arg): Adjust after renaming.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-ttp7.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 8cc5e21..3939132 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -8482,7 +8482,7 @@ is_compatible_template_arg (tree parm, tree arg, tree args)
         return false;
     }
 
-  return weakly_subsumes (parm_cons, arg);
+  return ttp_subsumes (parm_cons, arg);
 }
 
 // Convert a placeholder argument into a binding to the original