re PR libfortran/81984 (NULL string pointer dereferencing forces undefined…

re PR libfortran/81984 (NULL string pointer dereferencing forces undefined behaviour in libgfortran)

2018-12-28  Steven G. Kargl  <kargl@gcc.gnu.org>

	PR fortran/81984
	* intrinsics/string_intrinsics_inc.c: Placate the sanitizer.

From-SVN: r267452

libgfortran/ChangeLog

+2018-12-28  Steven G. Kargl  <kargl@gcc.gnu.org>
+
+	PR fortran/81984
+	* intrinsics/string_intrinsics_inc.c: Placate the sanitizer.
+
 2018-12-21  Steven G. Kargl  <kargl@gcc.gnu.org>
 
 	PR fortran/69121

libgfortran/intrinsics/string_intrinsics_inc.c

@@ -87,6 +87,14 @@ compare_string (gfc_charlen_type len1, const CHARTYPE *s1,
   gfc_charlen_type len;
   int res;
 
+  /* Placate the sanitizer.  */
+  if (!s1 && !s2)
+    return 0;
+  if (!s1)
+    return -1;
+  if (!s2)
+    return 1;
+
   res = MEMCMP (s1, s2, ((len1 < len2) ? len1 : len2));
   if (res != 0)
     return res;