re PR middle-end/21309 (internal compiler error: in expand_mult_const, at expmed.c:2884)

	PR middle-end/21309
	* expmed.c (choose_mult_variant): Return immediately when mult_cost
	is less than zero.  Limit mult_cost to a reasonable upper bound for
	the synthetic multiplication sequence.

From-SVN: r107537

gcc/ChangeLog

+2005-11-25  Roger Sayle  <roger@eyesopen.com>
+
+	PR middle-end/21309
+	* expmed.c (choose_mult_variant): Return immediately when mult_cost
+	is less than zero.  Limit mult_cost to a reasonable upper bound for
+	the synthetic multiplication sequence.
+
 2005-11-25  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>
 
 	PR middle-end/25022

gcc/expmed.c

@@ -2836,6 +2836,17 @@ choose_mult_variant (enum machine_mode mode, HOST_WIDE_INT val,
   struct mult_cost limit;
   int op_cost;
 
+  /* Fail quickly for impossible bounds.  */
+  if (mult_cost < 0)
+    return false;
+
+  /* Ensure that mult_cost provides a reasonable upper bound.
+     Any constant multiplication can be performed with less
+     than 2 * bits additions.  */
+  op_cost = 2 * GET_MODE_BITSIZE (mode) * add_cost[mode];
+  if (mult_cost > op_cost)
+    mult_cost = op_cost;
+
   *variant = basic_variant;
   limit.cost = mult_cost;
   limit.latency = mult_cost;