C++ PATCH for c++/71630 (extern variable template)

[Jason Merrill]

instantiate_decl's setting of pattern_defined never got adjusted for
variable templates; it was still checking DECL_IN_AGGR_P to decide
whether a static data member temploid is defined, which doesn't make
sense for namespace-scope variable templates.

Tested x86_64-pc-linux-gnu, applying to trunk, 5, 6.

commit 735ad45cb16c7703e1f5ec427c24b6809adb8ebb
Author: Jason Merrill <ja...@redhat.com>
Date:   Thu Jul 21 17:06:42 2016 -0400

        PR c++/71630 - extern variable template
    
        * pt.c (instantiate_decl): Fix pattern_defined for namespace scope
        variable templates.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index d7f3808..5e29d99 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -21853,7 +21853,10 @@ instantiate_decl (tree d, int defer_ok,
   else
     {
       deleted_p = false;
-      pattern_defined = ! DECL_IN_AGGR_P (code_pattern);
+      if (DECL_CLASS_SCOPE_P (code_pattern))
+       pattern_defined = ! DECL_IN_AGGR_P (code_pattern);
+      else
+       pattern_defined = ! DECL_EXTERNAL (code_pattern);
     }
 
   /* We may be in the middle of deferred access check.  Disable it now.  */
diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ53.C 
b/gcc/testsuite/g++.dg/cpp1y/var-templ53.C
new file mode 100644
index 0000000..3e30d67
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/var-templ53.C
@@ -0,0 +1,10 @@
+// PR c++/71630
+// { dg-do compile { target c++14 } }
+
+template <class T>
+extern T pi;
+
+int main()
+{
+  return pi<int>;
+}