C++ PATCH for variable templates in pack expansions

[Jason Merrill]

Looking at the concepts work led me to notice this bug: we weren't 
finding packs used only in variable template-ids.

Tested x86_64-pc-linux-gnu, applying to trunk.
commit 29ae93b90171f5202ec1de7507b77d09b2dff643
Author: Jason Merrill <ja...@redhat.com>
Date:   Fri Jul 10 15:27:11 2015 -0400
    	* pt.c (find_parameter_packs_r): Handle variable templates.
    	(variable_template_specialization_p): New.
    	* cp-tree.h: Declare it.

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index d383612..8450e9b 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -5771,6 +5771,7 @@ extern bool reregister_specialization		(tree, tree, tree);
 extern tree instantiate_non_dependent_expr	(tree);
 extern tree instantiate_non_dependent_expr_sfinae (tree, tsubst_flags_t);
 extern tree instantiate_non_dependent_expr_internal (tree, tsubst_flags_t);
+extern bool variable_template_specialization_p  (tree);
 extern bool alias_type_or_template_p            (tree);
 extern bool alias_template_specialization_p     (const_tree);
 extern bool dependent_alias_template_spec_p     (const_tree);
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 63907ce..8c72a61 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -3245,6 +3245,13 @@ find_parameter_packs_r (tree *tp, int *walk_subtrees, void* data)
 			ppd, ppd->visited);
 	  *walk_subtrees = 0;
 	}
+      else if (variable_template_specialization_p (t))
+	{
+	  cp_walk_tree (&DECL_TI_ARGS (t),
+			find_parameter_packs_r,
+			ppd, ppd->visited);
+	  *walk_subtrees = 0;
+	}
       break;
 
     case BASES:
@@ -5351,6 +5358,17 @@ instantiate_non_dependent_expr (tree expr)
   return instantiate_non_dependent_expr_sfinae (expr, tf_error);
 }
 
+/* True iff T is a specialization of a variable template.  */
+
+bool
+variable_template_specialization_p (tree t)
+{
+  if (!VAR_P (t) || !DECL_LANG_SPECIFIC (t) || !DECL_TEMPLATE_INFO (t))
+    return false;
+  tree tmpl = DECL_TI_TEMPLATE (t);
+  return variable_template_p (tmpl);
+}
+
 /* Return TRUE iff T is a type alias, a TEMPLATE_DECL for an alias
    template declaration, or a TYPE_DECL for an alias declaration.  */
 
diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ33.C b/gcc/testsuite/g++.dg/cpp1y/var-templ33.C
new file mode 100644
index 0000000..53c6db2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/var-templ33.C
@@ -0,0 +1,20 @@
+// Test for variable templates in pack expansion
+// { dg-do compile { target c++14 } }
+
+template <int I> const int Val = I;
+
+constexpr int f () { return 0; }
+template <class T, class ...Ts>
+constexpr int f(T t, Ts... ts)
+{
+  return t + f(ts...);
+}
+
+template <int... Is>
+constexpr int g()
+{
+  return f(Val<Is>...);
+}
+
+#define SA(X) static_assert((X),#X)
+SA((g<1,2,3,4>() == 1+2+3+4));