[gcc r12-8601] c++: non-dep call with empty TYPE_BINFO [PR105758]

[Patrick Palka]

https://gcc.gnu.org/g:4ebc9fef1ac36f353866c66b398e9bd0f1c2ed3d

commit r12-8601-g4ebc9fef1ac36f353866c66b398e9bd0f1c2ed3d
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue May 31 16:49:08 2022 -0400

    c++: non-dep call with empty TYPE_BINFO [PR105758]
    
    Here the out-of-line definition of Z<T>::z causes duplicate_decls to
    change z's type from using the primary template type Z<T> (which is also
    the type of the injected class name) to the implicit instantiation Z<T>,
    and this latter type lacks a TYPE_BINFO (although its TYPE_CANONICAL was
    set by a special case in lookup_template_class to point to the former).
    
    Later, when processing the non-dependent call z->foo(0), build_over_call
    relies on the object argument's TYPE_BINFO to build the templated form
    for this call, which fails because the object argument type has empty
    TYPE_BINFO due to the above.
    
    It seems weird that the implicit instantiation Z<T> doesn't have the
    same TYPE_BINFO as the primary template type Z<T>, despite them being
    proclaimed equivalent via TYPE_CANONICAL.  So I tried also setting
    TYPE_BINFO in the special case in lookup_template_class, but that led to
    some problems with constrained partial specializations of the form Z<T>.
    I'm not sure what, if anything, we ought to do about the subtle
    differences between these two versions of the same type.
    
    Fortunately it seems we don't need to rely on TYPE_BINFO at all in
    build_over_call here -- the z_candidate struct already contains the
    exact binfos we need to rebuild the BASELINK for the templated form.
    
            PR c++/105758
    
    gcc/cp/ChangeLog:
    
            * call.cc (build_over_call): Use z_candidate::conversion_path
            and ::access_path instead of TYPE_BINFO when building the
            BASELINK for the templated form.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/template/non-dependent24.C: New test.
    
    (cherry picked from commit 4f84f12066953186cce4328b7f178d3daa2fe96e)

Diff:
---
 gcc/cp/call.cc                                  |  4 ++--
 gcc/testsuite/g++.dg/template/non-dependent24.C | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index af92a961000..dafcdb08acb 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -9248,8 +9248,8 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
 	}
       else
 	{
-	  tree binfo = TYPE_BINFO (TREE_TYPE (first_arg));
-	  callee = build_baselink (binfo, binfo, fn, NULL_TREE);
+	  callee = build_baselink (cand->conversion_path, cand->access_path,
+				   fn, NULL_TREE);
 	  callee = build_min (COMPONENT_REF, TREE_TYPE (fn),
 			      first_arg, callee, NULL_TREE);
 	}
diff --git a/gcc/testsuite/g++.dg/template/non-dependent24.C b/gcc/testsuite/g++.dg/template/non-dependent24.C
new file mode 100644
index 00000000000..0ddc75c78ee
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent24.C
@@ -0,0 +1,19 @@
+// PR c++/105758
+
+struct A {
+  void foo(int);
+};
+
+template<class>
+struct Z : A {
+  static Z *z;
+  void bar();
+};
+
+template<class T>
+Z<T> *Z<T>::z;
+
+template<class T>
+void Z<T>::bar() {
+  z->foo(0);
+}