re PR c++/79655 (ICE on invalid c++ code in cxx_eval_store_expression in cp/constexpr.c:3464)

	PR c++/79655
	* constexpr.c (cxx_eval_array_reference): Diagnose negative subscript.

	* g++.dg/cpp1y/constexpr-79655.C: New test.

From-SVN: r245636

gcc/cp/ChangeLog

 2017-02-21  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/79655
+	* constexpr.c (cxx_eval_array_reference): Diagnose negative subscript.
+
 	PR c++/79639
 	* constexpr.c (cxx_eval_store_expression): If *valp is a PTRMEM_CST,
 	call cplus_expand_constant on it first.

gcc/cp/constexpr.c

@@ -2263,9 +2263,10 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree t,
   nelts = cxx_eval_constant_expression (ctx, nelts, false, non_constant_p,
 					overflow_p);
   VERIFY_CONSTANT (nelts);
-  if (lval
-      ? !tree_int_cst_le (index, nelts)
-      : !tree_int_cst_lt (index, nelts))
+  if ((lval
+       ? !tree_int_cst_le (index, nelts)
+       : !tree_int_cst_lt (index, nelts))
+      || tree_int_cst_sgn (index) < 0)
     {
       diag_array_subscript (ctx, ary, index);
       *non_constant_p = true;

gcc/testsuite/ChangeLog

 2017-02-21  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/79655
+	* g++.dg/cpp1y/constexpr-79655.C: New test.
+
 	PR c++/79639
 	* g++.dg/cpp1y/constexpr-79639.C: New test. 
 

gcc/testsuite/g++.dg/cpp1y/constexpr-79655.C

+// PR c++/79655
+// { dg-do compile { target c++14 } }
+
+constexpr int
+foo (int x, int y)
+{
+  int a[6] = { 1, 2, 3, 4, 5, 6 };
+  a[x] = 0;
+  return a[y];
+}
+
+constexpr int b = foo (0, -1);	// { dg-error "is outside the bounds" }
+constexpr int c = foo (0, 6);	// { dg-error "is outside the bounds" }
+constexpr int d = foo (6, 0);	// { dg-error "is outside the bounds" }
+constexpr int e = foo (-1, 0);	// { dg-error "is outside the bounds" }
+static_assert (foo (5, 5) == 0, "");
+static_assert (foo (4, 5) == 6, "");
+static_assert (foo (5, 4) == 5, "");