Small refinement to ipcp cost model

[Jan Hubicka <jh at suse dot cz>]

Hi,
ipcp now does some (bit rough) estimate on when cloning of function might save
size to setup propagation, but then we don't use that info when estimating
clonning costs after propagation. As a result we miss useful clones at -Os.
This nullify improvements on CSiBE I've seen during initial testing of ipcp.

Bootstrapped/regtested i686-linux, will commit it tonight.

/* { dg-do compile } */
/* { dg-options "-Os -fdump-ipa-cp"  } */

extern void t(int a);

void
i_am_rather_big (int parameter)
{
  t(parameter);
  t(parameter);
  t(parameter);
}

int call_many_times ()
{
  i_am_rather_big (1);
  i_am_rather_big (1);
  i_am_rather_big (1);
  i_am_rather_big (1);
  i_am_rather_big (1);
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}


/* { dg-final { scan-ipa-dump-times "versioned function" 1 "cp"  } } */
/* { dg-final { scan-ipa-dump "replacing param parameter with const 1" "cp"  } } */
/* { dg-final { cleanup-ipa-dump "cp" } } */


	* ipa-cp.c (ipcp_need_original_clone_p): Remove.
	(ipcp_estimate_growth): New.
	(ipcp_insert_stage): Use ipcp_estimate_growth.
Index: ipa-cp.c
===================================================================
--- ipa-cp.c	(revision 139829)
+++ ipa-cp.c	(working copy)
@@ -1042,22 +1042,59 @@ ipcp_update_profiling (void)
     }
 }
 
-/* Return true if original clone needs to be preserved.  */
-static bool
-ipcp_need_original_clone_p (struct cgraph_node *node)
+/* If NODE was cloned, how much would program grow? */
+static long
+ipcp_estimate_growth (struct cgraph_node *node)
 {
-  struct cgraph_edge *e;
+  struct cgraph_edge *cs;
+  int redirectable_node_callers = 0;
+  int removable_args = 0;
+  bool need_original = node->needed;
+  struct ipa_node_params *info;
+  int i, count;
+  int growth;
+
+  for (cs = node->callers; cs != NULL; cs = cs->next_caller)
+    if (!ipcp_need_redirect_p (cs))
+      redirectable_node_callers++;
+    else
+      need_original = true;
+
+  /* If we will be able to fully replace orignal node, we never increase
+     program size.  */
+  if (!need_original)
+    return false;
+
+  gcc_assert (redirectable_node_callers);
+  info = IPA_NODE_REF (node);
+  count = ipa_get_param_count (info);
+  for (i = 0; i < count; i++)
+    {
+      struct ipcp_lattice *lat = ipcp_get_ith_lattice (info, i);
+      tree parm_tree = ipa_get_ith_param (info, i);
 
-  if (node->needed)
-    return true;
-  for (e = node->callers; e; e = e->next_caller)
-    if (!bitmap_bit_p (dead_nodes, e->caller->uid)
-        && ipcp_need_redirect_p (e))
-      return true;
+      /* We can proactively remove obviously unused arguments.  */
+      if (is_gimple_reg (parm_tree)
+	  && !gimple_default_def (DECL_STRUCT_FUNCTION (node->decl),
+				  parm_tree))
+	removable_args++;
 
-  return false;
+      if (lat->type == IPA_CONST_VALUE)
+	removable_args++;
+    }
+
+  /* We make just very simple estimate of savings for removal of operand from
+     call site.  Precise cost is dificult to get, as our size metric counts
+     constants and moves as free.  Generally we are looking for cases that
+     small function is called very many times.  */
+  growth = node->local.inline_summary.self_insns
+  	   - removable_args * redirectable_node_callers;
+  if (growth < 0)
+    return 0;
+  return growth;
 }
 
+
 /* Estimate cost of cloning NODE.  */
 static long
 ipcp_estimate_cloning_cost (struct cgraph_node *node)
@@ -1067,12 +1104,12 @@ ipcp_estimate_cloning_cost (struct cgrap
   struct cgraph_edge *e;
   int cost;
 
-  /* When we don't need original clone; we should always propagate.  */
-  if (!ipcp_need_original_clone_p (node))
+  cost = ipcp_estimate_growth (node) * 1000;
+  if (!cost)
     {
       if (dump_file)
-	fprintf (dump_file, "Function %s can be fully propagated\n",
-		 cgraph_node_name (node));
+        fprintf (dump_file, "Versioning of %s will save code size\n",
+	         cgraph_node_name (node));
       return 0;
     }
 
@@ -1084,11 +1121,10 @@ ipcp_estimate_cloning_cost (struct cgrap
 	freq_sum += e->frequency + 1;
       }
 
-  cost = node->local.inline_summary.self_insns * 1000;
   if (max_count)
-    cost /= count_sum * 1000 / max_count + 1;
+    cost /= count_sum * 1000 / max_count + 1;
   else
-    cost /= freq_sum * 1000 / REG_BR_PROB_BASE + 1;
+    cost /= freq_sum * 1000 / REG_BR_PROB_BASE + 1;
   if (dump_file)
     fprintf (dump_file, "Cost of versioning %s is %i, (size: %i, freq: %i)\n",
              cgraph_node_name (node), cost, node->local.inline_summary.self_insns,
@@ -1185,10 +1221,7 @@ ipcp_insert_stage (void)
 	fprintf (dump_file, "considering function %s\n",
 		 cgraph_node_name (node));
 
-      if (ipcp_need_original_clone_p (node))
-        growth = node->local.inline_summary.self_insns;
-      else
-	bitmap_set_bit (dead_nodes, node->uid);
+      growth = ipcp_estimate_growth (node);
 
       if (new_insns + growth > max_new_insns)
 	break;