C++ PATCH for c++/84665, ICE with array of empty class

[Jason Merrill]

Another place we need to use fold_non_dependent_expr so that constant
evaluation happens in non-template context.

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

commit 1f7ec60303854ae6c79034223aba5ad996b86843
Author: Jason Merrill <ja...@redhat.com>
Date:   Thu Apr 5 10:46:27 2018 -0400

            PR c++/84665 - ICE with array of empty class.
    
            * decl2.c (cp_check_const_attributes): Use fold_non_dependent_expr.

diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
index 6078fb668a7..b0bf8241f71 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -1416,7 +1416,7 @@ cp_check_const_attributes (tree attributes)
 	{
 	  tree expr = TREE_VALUE (arg);
 	  if (EXPR_P (expr))
-	    TREE_VALUE (arg) = maybe_constant_value (expr);
+	    TREE_VALUE (arg) = fold_non_dependent_expr (expr);
 	}
     }
 }
diff --git a/gcc/testsuite/g++.dg/ext/attr-noinline-4.C b/gcc/testsuite/g++.dg/ext/attr-noinline-4.C
new file mode 100644
index 00000000000..27c7ae80fec
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/attr-noinline-4.C
@@ -0,0 +1,10 @@
+// PR c++/84665
+
+struct S {} a[1];
+
+template <int N>
+void
+foo ()
+{
+  __attribute__ ((noinline (a[0]))) int c = 0; // { dg-error "wrong number of arguments" }
+}