[Bug ipa/63671] [5 Regression] 21% tramp3d-v4 performance hit due to -fdevirtualize

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63671

--- Comment #5 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
There is also code size differnce. I tried to track it down and with
-fno-devirtualize I need to disable all places devirtualization happens:
Index: gimple-fold.c
===================================================================
--- gimple-fold.c       (revision 217304)
+++ gimple-fold.c       (working copy)
@@ -331,7 +331,7 @@ fold_gimple_assign (gimple_stmt_iterator
            tree val = OBJ_TYPE_REF_EXPR (rhs);
            if (is_gimple_min_invariant (val))
              return val;
-           else if (flag_devirtualize && virtual_method_call_p (rhs))
+           else if (flag_devirtualize && virtual_method_call_p (rhs) && 0)
              {
                bool final;
                vec <cgraph_node *>targets
@@ -2633,7 +2633,7 @@ gimple_fold_call (gimple_stmt_iterator *
          gimple_call_set_fn (stmt, OBJ_TYPE_REF_EXPR (callee));
          changed = true;
        }
-      else if (flag_devirtualize && !inplace && virtual_method_call_p
(callee))
+      else if (flag_devirtualize && !inplace && virtual_method_call_p (callee)
&& 0)
        {
          bool final;
          vec <cgraph_node *>targets
Index: ipa.c
===================================================================
--- ipa.c       (revision 217304)
+++ ipa.c       (working copy)
@@ -198,7 +198,7 @@ walk_polymorphic_call_targets (hash_set<
      final or anonymous (so we know all its derivation)
      and there is only one possible virtual call target,
      make the edge direct.  */
-  if (final)
+  if (final && 0)
     {
       if (targets.length () <= 1 && dbg_cnt (devirt))
        {
Index: tree-ssa-pre.c
===================================================================
--- tree-ssa-pre.c      (revision 217304)
+++ tree-ssa-pre.c      (working copy)
@@ -4320,7 +4320,7 @@ eliminate_dom_walker::before_dom_childre
        {
          tree fn = gimple_call_fn (stmt);
          if (fn
-             && flag_devirtualize
+             && flag_devirtualize && 0
              && virtual_method_call_p (fn))
            {
              tree otr_type = obj_type_ref_class (fn);

So apparently it is not the unit growth nor reachability code. It is simply
presence of direct calls instead of polymorphic calls that seems to make
inliner to do bad decisions...