string.c (rb_str_justify): use RB_GC_GUARD

See doc/extension.rdoc for justification using RB_GC_GUARD instead
of volatile.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51011 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,7 @@
+Wed Jun 24 16:05:42 2015  Eric Wong  <e@80x24.org>
+
+	* string.c (rb_str_justify): use RB_GC_GUARD
+
 Wed Jun 24 14:25:17 2015  Koichi Sasada  <ko1@atdot.net>
 
 	* gc.c (gc_mark_ptr): add a check code for #11244.

string.c

@@ -7908,7 +7908,7 @@ rb_str_justify(int argc, VALUE *argv, VALUE str, char jflag)
     char *p;
     const char *f = " ";
     long n, size, llen, rlen, llen2 = 0, rlen2 = 0;
-    volatile VALUE pad;
+    VALUE pad;
     int singlebyte = 1, cr;
 
     rb_scan_args(argc, argv, "11", &w, &pad);
@@ -7985,6 +7985,8 @@ rb_str_justify(int argc, VALUE *argv, VALUE str, char jflag)
 	cr = ENC_CODERANGE_AND(cr, ENC_CODERANGE(pad));
     if (cr != ENC_CODERANGE_BROKEN)
 	ENC_CODERANGE_SET(res, cr);
+
+    RB_GC_GUARD(pad);
     return res;
 }