[PR90916] ICE in retrieve specialization

https://gcc.gnu.org/ml/gcc-patches/2020-01/msg00809.html
	PR c++/90916
	* pt.c (retrieve_specialization): Get the TI from the decl or the
	classtype as appropriate.

gcc/cp/ChangeLog

+2020-01-14  Nathan Sidwell  <nathan@acm.org>
+
+	PR c++/90916
+	* pt.c (retrieve_specialization): Get the TI from the decl or the
+	classtype as appropriate.
+
 2020-01-14  David Malcolm  <dmalcolm@redhat.com>
 
 	* cp-gimplify.c (source_location_table_entry_hash::empty_zero_p):

gcc/cp/pt.c

@@ -1252,11 +1252,16 @@ retrieve_specialization (tree tmpl, tree args, hashval_t hash)
       for (ovl_iterator iter (fns); iter; ++iter)
 	{
 	  tree fn = *iter;
-	  if (DECL_TEMPLATE_INFO (fn) && DECL_TI_TEMPLATE (fn) == tmpl
-	      /* using-declarations can add base methods to the method vec,
-		 and we don't want those here.  */
-	      && DECL_CONTEXT (fn) == class_specialization)
-	    return fn;
+	  if (tree ti = (TREE_CODE (fn) == TYPE_DECL && !TYPE_DECL_ALIAS_P (fn)
+			 ? TYPE_TEMPLATE_INFO (TREE_TYPE (fn))
+			 : DECL_TEMPLATE_INFO (fn)))
+	    if (TI_TEMPLATE (ti) == tmpl
+		/* using-declarations can bring in a different
+		   instantiation of tmpl as a member of a different
+		   instantiation of tmpl's class.  We don't want those
+		   here.  */
+		&& DECL_CONTEXT (fn) == class_specialization)
+	      return fn;
 	}
       return NULL_TREE;
     }

gcc/testsuite/g++.dg/template/pr90916.C

+// PR c++/90916 ICE in retrieve_specialization
+
+template <typename> struct S
+{
+  struct A;
+  struct f A ();
+};
+template class S <int>;