c++: alias of alias tmpl with dependent attrs [PR115897]

As a follow-up to r15-2047-g7954bb4fcb6fa8, we also need to consider
dependent attributes when recursing into a non-template alias that names
a dependent alias template specialization (and so STF_STRIP_DEPENDENT
is set), otherwise in the first testcase below we undesirably strip B
all the way to T instead of to A<T>.

We also need to move the typedef recursion case of strip_typedefs up to
get checked before the compound type recursion cases.  Otherwise for C
below (which ultimately aliases T*) we end up stripping it to T* instead
of to A<T*> because the POINTER_TYPE recursion dominates the typedef
recursion.  It also means we issue an unexpected extra error in the
third testcase below.

Ideally we would also want to consider dependent attributes on
non-template aliases, so that we accept the second testcase below, but
making that work correctly would require broader changes to e.g.
structural_comptypes.

	PR c++/115897

gcc/cp/ChangeLog:

	* tree.cc (strip_typedefs): Move up the typedef recursion case.
	Never strip a dependent alias template-id that has dependent
	attributes.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/alias-decl-78.C: New test.
	* g++.dg/cpp0x/alias-decl-79.C: New test.
	* g++.dg/cpp0x/alias-decl-pr92206-1a.C: New test.

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

4 files changed, 110 insertions, 22 deletions

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 250239e..f2001ac 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -1607,11 +1607,32 @@ strip_typedefs (tree t, bool *remove_attributes /* = NULL */,
   if (t == TYPE_CANONICAL (t))
     return t;
 
-  if (!(flags & STF_STRIP_DEPENDENT)
-      && dependent_alias_template_spec_p (t, nt_opaque))
-    /* DR 1558: However, if the template-id is dependent, subsequent
-       template argument substitution still applies to the template-id.  */
-    return t;
+  if (typedef_variant_p (t))
+    {
+      if ((flags & STF_USER_VISIBLE)
+	  && !user_facing_original_type_p (t))
+	return t;
+
+      if (alias_template_specialization_p (t, nt_opaque))
+	{
+	  if (dependent_alias_template_spec_p (t, nt_opaque)
+	      && (!(flags & STF_STRIP_DEPENDENT)
+		  || any_dependent_type_attributes_p (DECL_ATTRIBUTES
+						      (TYPE_NAME (t)))))
+	    /* DR 1558: However, if the template-id is dependent, subsequent
+	       template argument substitution still applies to the template-id.  */
+	    return t;
+	}
+      else
+	/* If T is a non-template alias or typedef, we can assume that
+	   instantiating its definition will hit any substitution failure,
+	   so we don't need to retain it here as well.  */
+	flags |= STF_STRIP_DEPENDENT;
+
+      result = strip_typedefs (DECL_ORIGINAL_TYPE (TYPE_NAME (t)),
+			       remove_attributes, flags);
+      goto stripped;
+    }
 
   switch (TREE_CODE (t))
     {
@@ -1805,23 +1826,9 @@ strip_typedefs (tree t, bool *remove_attributes /* = NULL */,
     }
 
   if (!result)
-    {
-      if (typedef_variant_p (t))
-	{
-	  if ((flags & STF_USER_VISIBLE)
-	      && !user_facing_original_type_p (t))
-	    return t;
-	  /* If T is a non-template alias or typedef, we can assume that
-	     instantiating its definition will hit any substitution failure,
-	     so we don't need to retain it here as well.  */
-	  if (!alias_template_specialization_p (t, nt_opaque))
-	    flags |= STF_STRIP_DEPENDENT;
-	  result = strip_typedefs (DECL_ORIGINAL_TYPE (TYPE_NAME (t)),
-				   remove_attributes, flags);
-	}
-      else
-	result = TYPE_MAIN_VARIANT (t);
-    }
+    result = TYPE_MAIN_VARIANT (t);
+
+stripped:
   /*gcc_assert (!typedef_variant_p (result)
 	      || dependent_alias_template_spec_p (result, nt_opaque)
 	      || ((flags & STF_USER_VISIBLE)
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-78.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-78.C
new file mode 100644
index 0000000..a52c062
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-78.C
@@ -0,0 +1,34 @@
+// PR c++/115897
+// { dg-do compile { target c++11 } }
+
+template<class T, class U>
+struct is_same { static constexpr bool value = __is_same(T, U); };
+
+#if __cpp_variable_templates
+template<class T, class U>
+constexpr bool is_same_v = __is_same(T, U);
+#endif
+
+template<class T>
+using A [[gnu::vector_size(16)]] = T;
+
+template<class T>
+void f() {
+  using B = A<T>;
+  static_assert(!is_same<T, B>::value, "");
+#if __cpp_variable_templates
+  static_assert(!is_same_v<T, B>, "");
+#endif
+};
+
+template<class T>
+void g() {
+  using C = A<T*>;
+  static_assert(!is_same<T*, C>::value, "");
+#if __cpp_variable_templates
+  static_assert(!is_same_v<T*, C>, "");
+#endif
+};
+
+template void f<float>();
+template void g<float>();
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-79.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-79.C
new file mode 100644
index 0000000..e0f0747
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-79.C
@@ -0,0 +1,37 @@
+// PR c++/115897
+// { dg-do compile { target c++11 } }
+
+template<class T, class U>
+struct is_same { static constexpr bool value = __is_same(T, U); };
+
+#if __cpp_variable_templates
+template<class T, class U>
+constexpr bool is_same_v = __is_same(T, U);
+#endif
+
+template<class T> struct A;
+
+template<class T>
+void f() {
+  using B [[gnu::vector_size(16)]] = T;
+  static_assert(!is_same<T, B>::value, "");        // { dg-bogus "" "" { xfail *-*-* } }
+  static_assert(!is_same<A<T>, A<B>>::value, "");  // { dg-bogus "" "" { xfail *-*-* } }
+#if __cpp_variable_templates
+  static_assert(!is_same_v<T, B>, "");             // { dg-bogus "" "" { xfail c++14 } }
+  static_assert(!is_same_v<A<T>, A<B>>, "");       // { dg-bogus "" "" { xfail c++14 } }
+#endif
+};
+
+template<class T>
+void g() {
+  using C [[gnu::vector_size(16)]] = T*;
+  static_assert(!is_same<T*, C>::value, "");       // { dg-bogus "" "" { xfail *-*-* } }
+  static_assert(!is_same<A<T*>, A<C>>::value, ""); // { dg-bogus "" "" { xfail *-*-* } }
+#if __cpp_variable_templates
+  static_assert(!is_same_v<T*, C>, "");            // { dg-bogus "" "" { xfail c++14 } }
+  static_assert(!is_same_v<A<T*>, A<C>>, "");      // { dg-bogus "" "" { xfail c++14 } }
+#endif
+};
+
+template void f<float>();
+template void g<float>();
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-pr92206-1a.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-pr92206-1a.C
new file mode 100644
index 0000000..09781f6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-pr92206-1a.C
@@ -0,0 +1,10 @@
+// A version of alias-decl-pr92206-1.C where alias2 is a compound type.
+// { dg-require-effective-target c++11 }
+
+template<typename> struct A {};
+template<typename T1, typename T2 = typename T1::value> using alias1 = A<T1>;
+template<typename T> class B {
+  using alias2 = alias1<A<T>>*; // { dg-error {no type named 'value'} }
+  A<alias2> a; // { dg-bogus {no type named 'value'} }
+};
+B<int> b;