[Bug tree-optimization/33673] New: ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[Bug tree-optimization/33673] New: ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[janis at gcc dot gnu dot org]

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Benchmark 176.gcc from SPEC CPU2000 fails with an ICE in verify_flow_info and a
message about a missing barrier when compiled on powerpc-linux with "-Os
-fno-forward-propagate -fno-guess-branch-probability -fno-move-loop-invariants
-fno-tree-dominator-opts -fno-tree-loop-optimize".  It's an odd set of options
but the failure probably demonstrates some sort of dependency between the  
optimizations.  All of the options are documented, none as experimental.

A minimized test case (I'll attach it) fails with these options for a cross cc1
  for any of power*-*-*, s390*-linux, cris-elf, frv-elf, or m32c-elf with the
output:

  bug11.c: In function ‘find_reg’:
  bug11.c:32: error: missing barrier after block 4
  bug11.c:32: internal compiler error: verify_flow_info failed
  Please submit a full bug report,
  with preprocessed source if appropriate.
  See <http://gcc.gnu.org/bugs.html> for instructions.

The failure starts with this patch:

    http://gcc.gnu.org/viewcvs?view=rev&rev=124786

    r124786 | rakdver | 2007-05-17 08:10:24 +0000 (Thu, 17 May 2007)


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           Summary: ICE in verify_flow_info, missing barrier, when multiple
                    tree opts disabled
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: janis at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug tree-optimization/33673] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[janis at gcc dot gnu dot org]

------- Comment #1 from janis at gcc dot gnu dot org  2007-10-06 01:23 -------
Created an attachment (id=14309)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14309&action=view)
minimized testcase


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug rtl-optimization/33673] [4.3 Regression] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2007-10-06 01:30 -------
Even though the patch was for Tree level, the patch exposed a latent bug in the
rtl optimizers (missing barrier after can only happen on the rtl level).


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pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
          Component|tree-optimization           |rtl-optimization
           Keywords|                            |ice-on-valid-code
            Summary|ICE in verify_flow_info,    |[4.3 Regression] ICE in
                   |missing barrier, when       |verify_flow_info, missing
                   |multiple tree opts disabled |barrier, when multiple tree
                   |                            |opts disabled
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug rtl-optimization/33673] [4.3 Regression] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[steven at gcc dot gnu dot org]

------- Comment #3 from steven at gcc dot gnu dot org  2007-10-06 12:36 -------
10 to 1 this is a problem with coming out of cfglayout mode somewhere.


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steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |steven at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug rtl-optimization/33673] [4.3 Regression] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[mmitchel at gcc dot gnu dot org]

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mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug rtl-optimization/33673] [4.3 Regression] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[jakub at gcc dot gnu dot org]

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jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
                   |dot org                     |
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-10-11 12:53:19
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug rtl-optimization/33673] [4.3 Regression] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[jakub at gcc dot gnu dot org]

------- Comment #4 from jakub at gcc dot gnu dot org  2007-10-11 16:27 -------
If cprop_jump changes a conditional jump into unconditional, then it forgets
to add a BARRIER after it.  When not in cfglayout mode that's enough, but
in cfglayout mode it is uglier, though I haven't found a cfg hook which would
do what cprop_jump needs.


--- gcc/gcse.c.jj  2007-10-03 21:33:54.000000000 +0200
+++ gcc/gcse.c      2007-10-11 18:13:45.000000000 +0200
@@ -2853,6 +2853,14 @@ cprop_jump (basic_block bb, rtx setcc, r
       /* Remove REG_EQUAL note after simplification.  */
       if (note_src)
        remove_note (jump, note);
+
+      if (any_uncondjump_p (jump)
+         || (returnjump_p (jump) && !any_condjump_p (jump)))
+       {
+         rtx barrier = emit_barrier_after (jump);
+         if (current_ir_type () == IR_RTL_CFGLAYOUT)
+           bb->il.rtl->footer = unlink_insn_chain (barrier, barrier);
+       }
      }

 #ifdef HAVE_cc0

is ugly, but fixes this bug.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug rtl-optimization/33673] [4.3 Regression] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[steven at gcc dot gnu dot org]

------- Comment #6 from steven at gcc dot gnu dot org  2007-10-11 18:53 -------
The patch from comment #4 is wrong and should not be applied.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug rtl-optimization/33673] [4.3 Regression] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[steven at gcc dot gnu dot org]

------- Comment #5 from steven at gcc dot gnu dot org  2007-10-11 18:52 -------
What do the edge flags look like after cprop changes the jump?  EDGE_FALLTHRU
should be set.

Also, the unconditional JUMP_INSN should be removed.  Unconditional jumps are
removed when going into cfglayout mode, and when a conditional jump is turned
into  an unconditional jump, the whole JUMP_INSN can be removed.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug rtl-optimization/33673] [4.3 Regression] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[jakub at gcc dot gnu dot org]

------- Comment #7 from jakub at gcc dot gnu dot org  2007-10-11 19:29 -------
It calls purge_dead_edges after changing the jump, so if it changed that into
an unconditional jump, purge_dead_edges will purge the EDGE_FALLTHRU
edge and keep the other edge.

If cfglayout mode is supposed to avoid unconditional jumps, then that needs to
be changed, so that the old non-fallthrough edge becomes EDGE_FALLTHRU and old
EDGE_FALLTHRU is removed.  I believe in other cases cprop_jump could e.g. only
simplify an conditional jump (then what it does ATM is probably ok) or could
e.g. change a conditional returnjump_p into unconditional one (how are those
supposed to be expressed in cfglayout mode)?
Anyway, it seems both pass_gcse and pass_bypass are both always in cfglayout
mode, so no conditionalization on current_ir_type () is needed.


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jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|jakub at gcc dot gnu dot org|unassigned at gcc dot gnu
                   |                            |dot org
             Status|ASSIGNED                    |NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug rtl-optimization/33673] [4.3 Regression] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[steven at gcc dot gnu dot org]

------- Comment #8 from steven at gcc dot gnu dot org  2007-10-11 19:55 -------
Updating the CFG as suggested in comment #7 is the appropriate thing to do.

How about using delete_insn_and_edges() on the jump insn, and setting
EDGE_FALLTHRU on the remaining edge?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug rtl-optimization/33673] [4.3 Regression] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[jakub at gcc dot gnu dot org]

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jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
                   |dot org                     |
                URL|                            |http://gcc.gnu.org/ml/gcc-
                   |                            |patches/2007-
                   |                            |10/msg01845.html
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2007-10-11 12:53:19         |2007-10-31 10:29:42
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug rtl-optimization/33673] [4.3 Regression] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[jakub at gcc dot gnu dot org]

------- Comment #9 from jakub at gcc dot gnu dot org  2007-11-01 08:48 -------
Subject: Bug 33673

Author: jakub
Date: Thu Nov  1 08:48:05 2007
New Revision: 129819

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=129819
Log:
        PR rtl-optimization/33673
        * gcse.c (cprop_jump): If a conditional jump has been optimized
        into unconditional jump, make the remaining normal edge fallthru
        and delete the jump insn.

        * gcc.dg/pr33673.c: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/pr33673.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/gcse.c
    trunk/gcc/testsuite/ChangeLog


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673

[Bug rtl-optimization/33673] [4.3 Regression] ICE in verify_flow_info, missing barrier, when multiple tree opts disabled

[jakub at gcc dot gnu dot org]

------- Comment #10 from jakub at gcc dot gnu dot org  2007-11-01 08:49 -------
Fixed.


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jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33673