re PR c++/69496 ([C++ 14] ICE on VLA in constexpr function)

	PR c++/69496
	* constexpr.c (cxx_eval_array_reference): Evaluate the number of
	elements of the array.

	* g++.dg/ext/constexpr-vla1.C: New test.

From-SVN: r232875

gcc/cp/ChangeLog

+2016-01-27  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/69496
+	* constexpr.c (cxx_eval_array_reference): Evaluate the number of
+	elements of the array.
+
 2016-01-26  Jason Merrill  <jason@redhat.com>
 
 	PR c++/68949

gcc/cp/constexpr.c

@@ -1846,7 +1846,12 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree t,
 
   if (!found)
     {
-      if (tree_int_cst_lt (index, array_type_nelts_top (TREE_TYPE (ary))))
+      tree nelts = array_type_nelts_top (TREE_TYPE (ary));
+      /* For VLAs, the number of elements won't be an integer constant.  */
+      nelts = cxx_eval_constant_expression (ctx, nelts, false, non_constant_p,
+					    overflow_p);
+      VERIFY_CONSTANT (nelts);
+      if (tree_int_cst_lt (index, nelts))
 	{
 	  if (TREE_CODE (ary) == CONSTRUCTOR
 	      && CONSTRUCTOR_NO_IMPLICIT_ZERO (ary))

gcc/testsuite/ChangeLog

+2016-01-27  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/69496
+	* g++.dg/ext/constexpr-vla1.C: New test.
+
 2016-01-20  Christian Bruel  <christian.bruel@st.com>
 
 	PR target/69245

gcc/testsuite/g++.dg/ext/constexpr-vla1.C

+// PR c++/69496
+// { dg-do compile { target c++14 } }
+
+constexpr int
+fn_ok (int n)
+{
+    __extension__ int a[n] = { };
+    int z = 0;
+
+    for (unsigned i = 0; i < sizeof (a) / sizeof (int); ++i)
+      z += a[i];
+
+    return z;
+}
+
+
+constexpr int
+fn_not_ok (int n)
+{
+    __extension__ int a[n] = { };
+    int z = 0;
+
+    for (unsigned i = 0; i < sizeof (a); ++i)
+      z += a[i];
+
+    return z;
+}
+
+constexpr int n1 = fn_ok (3);
+constexpr int n2 = fn_not_ok (3); // { dg-error "array subscript out of bound" }