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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/35545] virtual call specialization not happening with FDO
Date: Tue, 17 Dec 2013 18:09:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35545

--- Comment #5 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
Main issue seems to be that VRP messes up on:
  # ap_2 = PHI <ap_8(5)>
  # prephitmp_14 = PHI <&MEM[(void *)&_ZTV1A + 16B](5)>
  _19 = *prephitmp_14;

here it somehow won't constant propagate the load. 
Index: passes.def
===================================================================
--- passes.def  (revision 206040)
+++ passes.def  (working copy)
@@ -236,6 +236,7 @@ along with GCC; see the file COPYING3.
       NEXT_PASS (pass_reassoc);
       NEXT_PASS (pass_strength_reduction);
       NEXT_PASS (pass_dominator);
+      NEXT_PASS (pass_tracer);
       /* The only const/copy propagation opportunities left after
         DOM should be due to degenerate PHI nodes.  So rather than
         run the full propagators, run a specialized pass which
@@ -244,7 +245,6 @@ along with GCC; see the file COPYING3.
       NEXT_PASS (pass_phi_only_cprop);
       NEXT_PASS (pass_vrp);
       NEXT_PASS (pass_cd_dce);
-      NEXT_PASS (pass_tracer);
       NEXT_PASS (pass_dse);
       NEXT_PASS (pass_forwprop);
       NEXT_PASS (pass_phiopt);

actually helps since phi_only_cprop is good on this transform. I do not quite
gather why VRP can't do it itself.

I sent first patch to http://gcc.gnu.org/ml/gcc-patches/2013-12/msg01517.html