PR c++/72766 - ICE with VLA

	* constexpr.c (cxx_eval_pointer_plus_expression): Check constancy
	of nelts.
	* cp-gimplify.c (cp_fully_fold): Only maybe_constant_value in
	C++11 and up.

From-SVN: r238957

gcc/cp/ChangeLog

+2016-08-01  Jason Merrill  <jason@redhat.com>
+
+	PR c++/72766
+	* constexpr.c (cxx_eval_pointer_plus_expression): Check constancy
+	of nelts.
+	* cp-gimplify.c (cp_fully_fold): Only maybe_constant_value in
+	C++11 and up.
+
 2016-07-30 Martin Sebor  <msebor@redhat.com>
 
 	PR c++/60760

gcc/cp/constexpr.c

@@ -3581,6 +3581,10 @@ cxx_eval_pointer_plus_expression (const constexpr_ctx *ctx, tree t,
       tree type = TREE_TYPE (op00);
       t = fold_convert_loc (loc, ssizetype, TREE_OPERAND (op00, 1));
       tree nelts = array_type_nelts_top (TREE_TYPE (TREE_OPERAND (op00, 0)));
+      nelts = cxx_eval_constant_expression (ctx, nelts, false, non_constant_p,
+					    overflow_p);
+      if (*non_constant_p)
+	return NULL_TREE;
       /* Don't fold an out-of-bound access.  */
       if (!tree_int_cst_le (t, nelts))
 	return NULL_TREE;

gcc/cp/cp-gimplify.c

@@ -1967,7 +1967,8 @@ cp_fully_fold (tree x)
     return x;
   /* FIXME cp_fold ought to be a superset of maybe_constant_value so we don't
      have to call both.  */
-  x = maybe_constant_value (x);
+  if (cxx_dialect >= cxx11)
+    x = maybe_constant_value (x);
   return cp_fold (x);
 }
 

gcc/testsuite/g++.dg/ext/vla16.C

+// PR c++/72766
+// { dg-options "-Wno-vla" }
+
+long fn1() {
+  const int a = fn1();
+  int b[a];
+  int c = *(&b[0] + sizeof(0));
+}