re PR fortran/77678 (ICE in fold_read_from_constant_string, at fold-const.c:13706)

2016-09-22  Richard Biener  <rguenther@suse.de>

	PR middle-end/77678
	* expr.c (expand_expr_real_1): Guard array access against negative
	offset.

From-SVN: r240351

gcc/ChangeLog

+2016-09-22  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/77678
+	* expr.c (expand_expr_real_1): Guard array access against negative
+	offset.
+
 2016-09-22  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	* gimple-ssa-sprintf.c (format_floating_max): Use GMP_RNDN instead

gcc/expr.c

@@ -10274,7 +10274,8 @@ expand_expr_real_1 (tree exp, rtx target, machine_mode tmode,
 					    fold_convert_loc (loc, sizetype,
 							      low_bound));
 
-		if (compare_tree_int (index1, TREE_STRING_LENGTH (init)) < 0)
+		if (tree_fits_uhwi_p (index1)
+		    && compare_tree_int (index1, TREE_STRING_LENGTH (init)) < 0)
 		  {
 		    tree type = TREE_TYPE (TREE_TYPE (init));
 		    machine_mode mode = TYPE_MODE (type);