re PR c++/69509 (infinite loop compiling a VLA in a recursive constexpr function)

	PR c++/69509
	PR c++/69516
	* constexpr.c (cxx_eval_array_reference): Give the "array subscript
	out of bound" error earlier.
	* init.c (build_vec_init): Change NE_EXPR into GT_EXPR.  Update the
	commentary.

	* g++.dg/ext/constexpr-vla2.C: New test.
	* g++.dg/ext/constexpr-vla3.C: New test.
	* g++.dg/ubsan/vla-1.C: Remove dg-shouldfail.

From-SVN: r232969

gcc/cp/ChangeLog

+2016-01-29  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/69509
+	PR c++/69516
+	* constexpr.c (cxx_eval_array_reference): Give the "array subscript
+	out of bound" error earlier.
+	* init.c (build_vec_init): Change NE_EXPR into GT_EXPR.  Update the
+	commentary.
+
 2016-01-29  Patrick Palka  <ppalka@gcc.gnu.org>
 
 	* name-lookup.c (begin_scope): After reusing a cp_binding_level

gcc/cp/constexpr.c

@@ -1833,6 +1833,19 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree t,
       return t;
     }
 
+  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 (!ctx->quiet)
+	error ("array subscript out of bound");
+      *non_constant_p = true;
+      return t;
+    }
+
   bool found;
   if (TREE_CODE (ary) == CONSTRUCTOR)
     {
@@ -1846,37 +1859,23 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree t,
 
   if (!found)
     {
-      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))
 	{
-	  if (TREE_CODE (ary) == CONSTRUCTOR
-	      && CONSTRUCTOR_NO_IMPLICIT_ZERO (ary))
-	    {
-	      /* 'ary' is part of the aggregate initializer we're currently
-		 building; if there's no initializer for this element yet,
-		 that's an error. */
-	      if (!ctx->quiet)
-		error ("accessing uninitialized array element");
-	      *non_constant_p = true;
-	      return t;
-	    }
-
-	  /* If it's within the array bounds but doesn't have an explicit
-	     initializer, it's value-initialized.  */
-	  tree val = build_value_init (elem_type, tf_warning_or_error);
-	  return cxx_eval_constant_expression (ctx, val,
-					       lval,
-					       non_constant_p, overflow_p);
+	  /* 'ary' is part of the aggregate initializer we're currently
+	     building; if there's no initializer for this element yet,
+	     that's an error.  */
+	  if (!ctx->quiet)
+	    error ("accessing uninitialized array element");
+	  *non_constant_p = true;
+	  return t;
 	}
 
-      if (!ctx->quiet)
-	error ("array subscript out of bound");
-      *non_constant_p = true;
-      return t;
+      /* If it's within the array bounds but doesn't have an explicit
+	 initializer, it's value-initialized.  */
+      tree val = build_value_init (elem_type, tf_warning_or_error);
+      return cxx_eval_constant_expression (ctx, val, lval, non_constant_p,
+					   overflow_p);
     }
 
   if (TREE_CODE (ary) == CONSTRUCTOR)

gcc/cp/init.c

@@ -4008,7 +4008,7 @@ build_vec_init (tree base, tree maxindex, tree init,
 		&& (num_initialized_elts
 		    == tree_to_shwi (maxindex) + 1))))
     {
-      /* If the ITERATOR is equal to -1, then we don't have to loop;
+      /* If the ITERATOR is lesser or equal to -1, then we don't have to loop;
 	 we've already initialized all the elements.  */
       tree for_stmt;
       tree elt_init;
@@ -4016,7 +4016,7 @@ build_vec_init (tree base, tree maxindex, tree init,
 
       for_stmt = begin_for_stmt (NULL_TREE, NULL_TREE);
       finish_for_init_stmt (for_stmt);
-      finish_for_cond (build2 (NE_EXPR, boolean_type_node, iterator,
+      finish_for_cond (build2 (GT_EXPR, boolean_type_node, iterator,
 			       build_int_cst (TREE_TYPE (iterator), -1)),
 		       for_stmt, false);
       elt_init = cp_build_unary_op (PREDECREMENT_EXPR, iterator, 0,

gcc/testsuite/ChangeLog

+2016-01-29  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/69509
+	PR c++/69516
+	* g++.dg/ext/constexpr-vla2.C: New test.
+	* g++.dg/ext/constexpr-vla3.C: New test.
+	* g++.dg/ubsan/vla-1.C: Remove dg-shouldfail.
+
 2016-01-29  Richard Biener  <rguenther@suse.de>
 
 	PR middle-end/69537

gcc/testsuite/g++.dg/ext/constexpr-vla2.C

+// PR c++/69509
+// { dg-do compile { target c++14 } }
+
+constexpr int
+fn_bad (int n)
+{
+  __extension__ int a [n] = { 0 };
+  int z = a [0] + (n ? fn_bad (n - 1) : 0);
+  return z;
+}
+
+constexpr int
+fn_ok (int n)
+{
+  __extension__ int a [n] = { 0 };
+  int z = a [0] + (n > 1 ? fn_ok (n - 1) : 0);
+  return z;
+}
+
+constexpr int i1 = fn_ok (3);
+constexpr int i2 = fn_bad (3); // { dg-error "array subscript out of bound" }

gcc/testsuite/g++.dg/ext/constexpr-vla3.C

+// PR c++/69516
+// { dg-do compile { target c++14 } }
+
+constexpr int
+foo (int n)
+{
+  __extension__ int a[n] = { 1, 2, 3, 4, 5, 6 };
+  int z = 0;
+  for (int i = 0; i <= n; ++i)
+    z += a[i];
+  return z;
+}
+
+constexpr int n = foo (3); // { dg-error "array subscript out of bound" }

gcc/testsuite/g++.dg/ubsan/vla-1.C

 // { dg-do run }
 // { dg-options "-Wno-vla -fsanitize=undefined" }
-// { dg-shouldfail "ubsan" }
 // { dg-output "index 1 out of bounds" }
 
 void f(int i) {