[gcc r13-4686] ipa-cp: Leave removal of unused parameters to IPA-SRA

[gcc r13-4686] ipa-cp: Leave removal of unused parameters to IPA-SRA

[Martin Jambor]

https://gcc.gnu.org/g:095a13eda2caf6842096a3ab78b2081c50fe8799

commit r13-4686-g095a13eda2caf6842096a3ab78b2081c50fe8799
Author: Martin Jambor <mjambor@suse.cz>
Date:   Wed Dec 14 00:33:05 2022 +0100

    ipa-cp: Leave removal of unused parameters to IPA-SRA
    
    Looking at some benchmarks I have noticed many cases when IPA-CP
    cloned a function for all contexts just because it knew that some
    parameters were not used at all.  Then IPA-SRA looked at the function
    and cloned it again to split another parameter or two.  The latter
    pass is better equipped to detect when parameters can be altogether
    removed and so the IPA-CP cloning was for no good reason.
    
    This patch simply alters the IPA-CP not to do that in the situations
    where IPA-SRA can (for nodes which can be made local) with additional
    dumping requested by Honza.
    
    gcc/ChangeLog:
    
    2022-12-13  Martin Jambor  <mjambor@suse.cz>
    
            * ipa-cp.cc (clone_for_param_removal_p): New function.
            (estimate_local_effects): Call it before considering cloning
            just to remove unused parameters.

Diff:
---
 gcc/ipa-cp.cc | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/gcc/ipa-cp.cc b/gcc/ipa-cp.cc
index cc031ebed0f..300bec54bbd 100644
--- a/gcc/ipa-cp.cc
+++ b/gcc/ipa-cp.cc
@@ -3700,6 +3700,29 @@ get_max_overall_size (cgraph_node *node)
   return max_new_size;
 }
 
+/* Return true if NODE should be cloned just for a parameter removal, possibly
+   dumping a reason if not.  */
+
+static bool
+clone_for_param_removal_p (cgraph_node *node)
+{
+  if (!node->can_change_signature)
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file, "  Not considering cloning to remove parameters, "
+		 "function cannot change signature.\n");
+      return false;
+    }
+  if (node->can_be_local_p ())
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file, "  Not considering cloning to remove parameters, "
+		 "IPA-SRA can do it potentially better.\n");
+      return false;
+    }
+  return true;
+}
+
 /* Iterate over known values of parameters of NODE and estimate the local
    effects in terms of time and size they have.  */
 
@@ -3722,7 +3745,7 @@ estimate_local_effects (struct cgraph_node *node)
 						    &removable_params_cost);
   int devirt_bonus = devirtualization_time_bonus (node, &avals);
   if (always_const || devirt_bonus
-      || (removable_params_cost && node->can_change_signature))
+      || (removable_params_cost && clone_for_param_removal_p (node)))
     {
       struct caller_statistics stats;
       ipa_call_estimates estimates;