[PATCH] Fix undefined behavior in ira-build.c

[Jakub Jelinek]

Hi!

This fixes the most common source of the new runtime diagnostics
during bootstrap-ubsan, if num is 0, ira_object_id_map is often
0 as well.

Ok for trunk/4.9?

2014-06-27  Jakub Jelinek  <ja...@redhat.com>

        * ira-build.c (sort_conflict_id_map): Don't call
        qsort if num is 0, as ira_object_id_map might be NULL.

--- gcc/ira-build.c.jj  2014-05-30 10:51:16.000000000 +0200
+++ gcc/ira-build.c     2014-06-26 20:21:43.428987181 +0200
@@ -2821,8 +2821,9 @@ sort_conflict_id_map (void)
       FOR_EACH_ALLOCNO_OBJECT (a, obj, oi)
        ira_object_id_map[num++] = obj;
     }
-  qsort (ira_object_id_map, num, sizeof (ira_object_t),
-        object_range_compare_func);
+  if (num)
+    qsort (ira_object_id_map, num, sizeof (ira_object_t),
+          object_range_compare_func);
   for (i = 0; i < num; i++)
     {
       ira_object_t obj = ira_object_id_map[i];

        Jakub