sel-sched: allow negative insn priority (PR 88879)

	PR rtl-optimization/88879
	* sel-sched.c (sel_target_adjust_priority): Remove assert.

From-SVN: r271039

gcc/ChangeLog

+2019-05-09  Alexander Monakov  <amonakov@ispras.ru>
+
+	PR rtl-optimization/88879
+	* sel-sched.c (sel_target_adjust_priority): Remove assert.
+
 2019-05-09  Richard Earnshaw  <rearnsha@arm.com>
 
 	PR target/90405

gcc/sel-sched.c

@@ -3331,8 +3331,6 @@ sel_target_adjust_priority (expr_t expr)
   else
     new_priority = priority;
 
-  gcc_assert (new_priority >= 0);
-
   /* If the priority has changed, adjust EXPR_PRIORITY_ADJ accordingly.  */
   EXPR_PRIORITY_ADJ (expr) = new_priority - EXPR_PRIORITY (expr);