PR c++/81586 - valgrind error in output_buffer_append_r with -Wall

gcc/ChangeLog:

	PR c++/81586
	* pretty-print.c (pp_format): Correct the handling of %s precision.

From-SVN: r251029

gcc/ChangeLog

+2017-08-10  Martin Sebor  <msebor@redhat.com>
+
+	PR c++/81586
+	* pretty-print.c (pp_format): Correct the handling of %s precision.
+
 2017-08-10  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/81736

gcc/pretty-print.c

@@ -667,7 +667,17 @@ pp_format (pretty_printer *pp, text_info *text)
 	      }
 
 	    s = va_arg (*text->args_ptr, const char *);
-	    pp_append_text (pp, s, s + n);
+
+	    /* Negative precision is treated as if it were omitted.  */
+	    if (n < 0)
+	      n = INT_MAX;
+
+	    /* Append the lesser of precision and strlen (s) characters.  */
+	    size_t len = strlen (s);
+	    if ((unsigned) n < len)
+	      len = n;
+
+	    pp_append_text (pp, s, s + len);
 	  }
 	  break;