[Bug middle-end/30905] [dataflow] Fails to cross-jump

[steven at gcc dot gnu dot org]

--- Comment #3 from steven at gcc dot gnu dot org  2007-05-08 23:15 ---
This patch would fix it, but it's brute-force and it causes a ~1.5% slowdown. 
Some form of DCE a little more delicate than this will be necessary to fix this
bug, though.


Index: cfgcleanup.c
===
--- cfgcleanup.c(revision 124550)
+++ cfgcleanup.c(working copy)
@@ -2286,10 +2286,10 @@ cleanup_cfg (int mode)
 {
   delete_unreachable_blocks (), changed = true;
   if (!(mode  CLEANUP_NO_INSN_DEL)
-  (mode  CLEANUP_EXPENSIVE)
-  !reload_completed)
+  (mode  (CLEANUP_EXPENSIVE | CLEANUP_CROSSJUMP)))
{
- if (!delete_trivially_dead_insns (get_insns (), max_reg_num ()))
+ gcc_assert (df);
+ if (! run_fast_dce ())
break;
}
   else
@@ -2343,10 +2343,9 @@ static unsigned int
 rest_of_handle_jump2 (void)
 {
   delete_trivially_dead_insns (get_insns (), max_reg_num ());
+  delete_unreachable_blocks ();
   if (dump_file)
 dump_flow_info (dump_file, dump_flags);
-  cleanup_cfg ((optimize ? CLEANUP_EXPENSIVE : 0)
-  | (flag_thread_jumps ? CLEANUP_THREADING : 0));
   return 0;
 }


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30905

[Bug middle-end/30905] [dataflow] Fails to cross-jump

[steven at gcc dot gnu dot org]

--- Comment #1 from steven at gcc dot gnu dot org  2007-02-21 20:59 ---
Confirmed, we almost never do cross-jumping on the dataflow-branch anymore:
only after regmove.


-- 

steven at gcc dot gnu dot org changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
 Ever Confirmed|0   |1
   Last reconfirmed|-00-00 00:00:00 |2007-02-21 20:59:58
   date||


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30905

[Bug middle-end/30905] [dataflow] Fails to cross-jump

[steven at gcc dot gnu dot org]

--- Comment #2 from steven at gcc dot gnu dot org  2007-02-21 22:09 ---
On the trunk, *and* on the dataflow branch, we crossjump the code starting with
if (i != 1) on the first cleanup_cfg iteration when it's called from
rest_of_handle_stack_adjustments.  Trunk then goes on to crossjump the other
blocks, but the df-branch stops because there is a set to the CC-reg in the
way. That set has a REG_UNUSED flag on it.

What probably happens, is that flow on the trunk does some dce in the liveness
update, and the df-branch does not.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30905