c++: Avoid ICE with dependent attribute on type.

We previously happened to accept this testcase, but never actually did
anything useful with the attribute.  The patch for PR86379 stopped using
TREE_TYPE as USING_DECL_SCOPE, so 'using A::b' no longer had TREE_TYPE set,
so the language-independent decl_attributes started crashing on it.

GNU attributes are more flexible in their placement than C++11 attributes,
so if we encounter a dependent GNU attribute that syntactically appertains
to a type rather than the declaration as a whole, move it to the
declaration; that's almost certainly what the user meant, anyway.

gcc/cp/ChangeLog
2020-04-27  Jason Merrill  <jason@redhat.com>

	PR c++/90750
	PR c++/79585
	* decl.c (grokdeclarator): Move dependent attribute to decl.
	* decl2.c (splice_template_attributes): No longer static.

gcc/cp/ChangeLog

+2020-04-27  Jason Merrill  <jason@redhat.com>
+
+	PR c++/90750
+	PR c++/79585
+	* decl.c (grokdeclarator): Move dependent attribute to decl.
+	* decl2.c (splice_template_attributes): No longer static.
+
 2020-04-27  Patrick Palka  <ppalka@redhat.com>
 
 	PR c++/94772

gcc/cp/cp-tree.h

@@ -6626,6 +6626,7 @@ extern tree grokfield (const cp_declarator *, cp_decl_specifier_seq *,
 		       tree, bool, tree, tree);
 extern tree grokbitfield (const cp_declarator *, cp_decl_specifier_seq *,
 			  tree, tree, tree);
+extern tree splice_template_attributes		(tree *, tree);
 extern bool any_dependent_type_attributes_p	(tree);
 extern tree cp_reconstruct_complex_type		(tree, tree);
 extern bool attributes_naming_typedef_ok	(tree);

gcc/cp/decl.c

@@ -11937,9 +11937,13 @@ grokdeclarator (const cp_declarator *declarator,
 	    attr_flags |= (int) ATTR_FLAG_FUNCTION_NEXT;
 	  if (declarator->kind == cdk_array)
 	    attr_flags |= (int) ATTR_FLAG_ARRAY_NEXT;
+	  /* Assume that any attributes that get applied late to templates will
+	     DTRT when applied to the declaration as a whole.  */
+	  tree late_attrs = splice_template_attributes (&attrs, type);
 	  returned_attrs = decl_attributes (&type,
 					    chainon (returned_attrs, attrs),
 					    attr_flags);
+	  returned_attrs = chainon (late_attrs, returned_attrs);
 	}
 
       inner_declarator = declarator->declarator;

gcc/cp/decl2.c

@@ -1228,7 +1228,7 @@ is_late_template_attribute (tree attr, tree decl)
    the declaration itself is dependent, so all attributes should be applied
    at instantiation time.  */
 
-static tree
+tree
 splice_template_attributes (tree *attr_p, tree decl)
 {
   tree *p = attr_p;

gcc/testsuite/g++.dg/ext/attr-type1.C

+// PR c++/90750
+// { dg-do compile { target c++11 } }
+
+template <typename> struct S
+{
+  static const int b = 64;
+};
+
+template <typename a> struct T: S<a>
+{
+  using A = S<a>;
+  using A::b;
+  char* __attribute__((aligned(b))) c;
+};
+
+T<int> t;
+
+#define SA(X) static_assert (X,#X)
+SA (alignof(T<int>) == S<int>::b);

gcc/testsuite/g++.dg/warn/Wunused-var-26.C

@@ -47,10 +47,10 @@ template <class T>
 void f_var_type_unused ()
 {
   // The variable's type is marked unused.
-  T* UNUSED t = new T;   // { dg-bogus "unused variable" "bug 79585" { xfail *-*-* } }
+  T* UNUSED t = new T;   // { dg-bogus "unused variable" "bug 79585" }
 
   typedef T U;
-  U* UNUSED u = new U;   // { dg-bogus "unused variable" "bug 79585" { xfail *-*-* } }
+  U* UNUSED u = new U;   // { dg-bogus "unused variable" "bug 79585" }
 
   typedef T UNUSED U;
   U v = U ();   // { dg-bogus "unused variable" "bug 79585" }