* params.def (PARAM_MAX_ITERATIONS_COMPUTATION_COST): New.

	* loop-doloop.c (doloop_optimize): Use it to limit costs of
	expanding the number of iterations.



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@116966 138bc75d-0d04-0410-961f-82ee72b054a4

gcc/ChangeLog

@@ -1,3 +1,9 @@
+2005-09-15  Bernd Schmidt  <[email protected]>
+
+	* params.def (PARAM_MAX_ITERATIONS_COMPUTATION_COST): New.
+	* loop-doloop.c (doloop_optimize): Use it to limit costs of
+	expanding the number of iterations.
+
 2006-09-15  Kazu Hirata  <[email protected]>
 
 	* doc/tm.texi (TARGET_FUNCTION_VALUE): Put @deftypefn all in

gcc/loop-doloop.c

@@ -484,7 +484,7 @@ doloop_optimize (struct loop *loop)
   rtx iterations_max;
   rtx start_label;
   rtx condition;
-  unsigned level, est_niter;
+  unsigned level, est_niter, max_cost;
   struct niter_desc *desc;
   unsigned word_mode_size;
   unsigned HOST_WIDE_INT word_mode_max;
@@ -525,6 +525,17 @@ doloop_optimize (struct loop *loop)
       return false;
     }
 
+  max_cost
+    = COSTS_N_INSNS (PARAM_VALUE (PARAM_MAX_ITERATIONS_COMPUTATION_COST));
+  if (rtx_cost (desc->niter_expr, SET) > max_cost)
+    {
+      if (dump_file)
+	fprintf (dump_file,
+		 "Doloop: number of iterations too costly to compute.\n",
+		 est_niter);
+      return false;
+    }
+
   count = copy_rtx (desc->niter_expr);
   iterations = desc->const_iter ? desc->niter_expr : const0_rtx;
   iterations_max = GEN_INT (desc->niter_max);

gcc/params.def

@@ -292,6 +292,12 @@ DEFPARAM(PARAM_MAX_ITERATIONS_TO_TRACK,
 	"max-iterations-to-track",
 	"Bound on the number of iterations the brute force # of iterations analysis algorithm evaluates",
 	1000, 0, 0)
+/* A cutoff to avoid costly computations of the number of iterations in
+   the doloop transformation.  */
+DEFPARAM(PARAM_MAX_ITERATIONS_COMPUTATION_COST,
+	"max-iterations-computation-cost",
+	"Bound on the cost of an expression to compute the number of iterations",
+	10, 0, 0)
 
 DEFPARAM(PARAM_MAX_SMS_LOOP_NUMBER,
 	 "max-sms-loop-number",