re PR middle-end/28071 (A file that can not be compiled in reasonable time/space)

	PR rtl-optimization/28071
	* cselib.c (cselib_process_insn): Don't remove useless values too
	often for very large hashtables.

From-SVN: r115777

gcc/ChangeLog

 2006-07-27  Jan Hubicka  <jh@suse.cz>
 
 	PR rtl-optimization/28071
+	* cselib.c (cselib_process_insn): Don't remove useless values too
+	often for very large hashtables.
+
+2006-07-27  Jan Hubicka  <jh@suse.cz>
+
+	PR rtl-optimization/28071
 	* global.c (greg_obstack): New obstack.
 	(allocate_bb_info): Use it.
 	(free_bb_info): Likewise.

gcc/cselib.c

@@ -1437,7 +1437,11 @@ cselib_process_insn (rtx insn)
     cselib_current_insn_in_libcall = false;
   cselib_current_insn = 0;
 
-  if (n_useless_values > MAX_USELESS_VALUES)
+  if (n_useless_values > MAX_USELESS_VALUES
+      /* remove_useless_values is linear in the hash table size.  Avoid
+         quadratic behaviour for very large hashtables with very few
+	 useless elements.  */
+      && (unsigned int)n_useless_values > cselib_hash_table->n_elements / 4)
     remove_useless_values ();
 }