[Bug tree-optimization/77445] [7 Regression] Performance drop after r239219 on coremark test

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77445

--- Comment #15 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
Note that the remaining missed threads loop exit condition test state !=
INVALID which after sequence of threads gets to probability 0 because original
guess from profile_estimate is not realistic.

I guess such repeated threading may be common. It may be interesting to
benchmark the following hack both for speed and size:

Index: tree-ssa-threadbackward.c
===================================================================
--- tree-ssa-threadbackward.c   (revision 244527)
+++ tree-ssa-threadbackward.c   (working copy)
@@ -311,7 +311,11 @@ profitable_jump_thread_path (vec<basic_b
       return NULL;
     }

-  if (speed_p && optimize_edge_for_speed_p (taken_edge))
+  if (speed_p
+      && (optimize_edge_for_speed_p (taken_edge)
+         || optimize_edge_for_speed_p (find_edge
+                                         ((*path)[path->length () - 1],
+                                          (*path)[path->length () - 2]))))
     {
       if (n_insns >= PARAM_VALUE (PARAM_MAX_FSM_THREAD_PATH_INSNS))
        {

It makes us to consider threading the path if at least it starts by an hot
edge.