middle-end/94465 - handle released SSA names in array_ref_low_bound

array_ref_low_bound is used in dumping ARRAY_REFs which in turn
is called when basic blocks are deleted.  cleanup_control_flow_pre
consciously decides to remove unreachable basic-blocks in arbitrary
order so the following makes array_ref_low_bound forgiving in the
case the SSA name with the index definition has been released
already.

2020-04-03  Richard Biener  <rguenther@suse.de>

	PR middle-end/94465
	* tree.c (array_ref_low_bound): Deal with released SSA names
	in index position.

gcc/ChangeLog

+2020-04-03  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/94465
+	* tree.c (array_ref_low_bound): Deal with released SSA names
+	in index position.
+
 2020-04-03  Kwok Cheung Yeung  <kcy@codesourcery.com>
 
 	* config/gcn/gcn.c (print_operand): Handle unordered comparison

gcc/tree.c

@@ -13426,7 +13426,9 @@ array_ref_low_bound (tree exp)
     return SUBSTITUTE_PLACEHOLDER_IN_EXPR (TYPE_MIN_VALUE (domain_type), exp);
 
   /* Otherwise, return a zero of the appropriate type.  */
-  return build_int_cst (TREE_TYPE (TREE_OPERAND (exp, 1)), 0);
+  tree idxtype = TREE_TYPE (TREE_OPERAND (exp, 1));
+  return (idxtype == error_mark_node
+	  ? integer_zero_node : build_int_cst (idxtype, 0));
 }
 
 /* Return a tree representing the upper bound of the array mentioned in