[Bug tree-optimization/39132] New: wrong code generated with -ftree-loop-disttribution

[Bug tree-optimization/39132] New: wrong code generated with -ftree-loop-disttribution

[kazu at gcc dot gnu dot org]

The following testcase calls abort when it is compiled with
-O3 -ftree-loop-distribution.

/* Derived from gcc.c-torture/execute/20010910-1.c.  */

extern void abort(void);

struct epic_private
{
  unsigned int *rx_ring;
  unsigned int rx_skbuff[5];
};

int
main (void)
{
  struct epic_private ep;
  unsigned int rx_ring[5];
  int i;

  ep.rx_skbuff[0] = 5;

  ep.rx_ring = rx_ring;

  for (i = 0; i < 5; i++)
    {
      ep.rx_ring[i] = i;
      ep.rx_skbuff[i] = 0;
    }

  if (ep.rx_skbuff[0] != 0)
    abort ();

  return 0;
}

The loop distribution pass produces:

<bb 2>:
  ep.rx_skbuff[0] = 5;

<bb 8>:
  # i_22 = PHI <i_36(9), 0(2)>
  D.1604_11 = (long unsigned int) i_22;
  D.1605_30 = D.1604_11 * 4;
  D.1606_31 = &rx_ring + D.1605_30;
  i.0_32 = (unsigned int) i_22;
  *D.1606_31 = i.0_32;
  i_36 = i_22 + 1;
  if (i_36 <= 4)
    goto <bb 9>;
  else
    goto <bb 10>;

<bb 9>:
  goto <bb 8>;

<bb 10>:
Invalid sum of outgoing probabilities 0.0%
  D.1642_37 = &ep + 8;
  __builtin_memset (D.1642_37, 0, 20);

<bb 5>:
Invalid sum of incoming frequencies 0, should be 1667
  D.1609_10 = ep.rx_skbuff[0];
  if (D.1609_10 != 0)
    goto <bb 6>;
  else
    goto <bb 7>;

<bb 6>:
  abort ();

<bb 7>:
  return 0;

dom2 in turn produces:

  ep.rx_skbuff[0] = 5;
  rx_ring[0] = 0;
  D.1606_47 = &rx_ring[1];
  rx_ring[1] = 1;
  D.1606_59 = &rx_ring[2];
  rx_ring[2] = 2;
  D.1606_71 = &rx_ring[3];
  rx_ring[3] = 3;
  D.1606_31 = &rx_ring[4];
  rx_ring[4] = 4;
  D.1642_37 = &ep + 8;
  __builtin_memset (D.1642_37, 0, 20);
  D.1609_10 = 5;
  abort ();

Note that the end of the function is replaced with an unconditional
abort.

GCC puts an unconditional abort at the rtl level when compiling The
original gcc.c-torture/execute/20010910-1.c.  Once I remove extra
source code, I can observe an unconditional abort at the tree level.

The compiler probably does not notice that the value of
ep.rx_skbuff[0] changes across __builtin_memset.  This sounds like an
alias problem of some sort.


-- 
           Summary: wrong code generated with -ftree-loop-disttribution
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at gcc dot gnu dot org
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39132

[Bug tree-optimization/39132] wrong code generated with -ftree-loop-disttribution

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2009-02-10 13:15 -------
Confirmed.  There is wrong alias-information on the memset:

<bb 10>:
Invalid sum of outgoing probabilities 0.0%
  D.1641_35 = &ep + 8;
  # rx_ring_36 = VDEF <rx_ring_31>
  # SMT.12_37 = VDEF <SMT.12_32>
  __builtin_memset (D.1641_35, 0, 20);

<bb 5>:
Invalid sum of incoming frequencies 0, should be 1667
  # VUSE <ep_15>
  D.1609_10 = ep.rx_skbuff[0];
  if (D.1609_10 != 0)

the memset should clobber ep.  Investigating.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-02-10 13:15:51
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39132

[Bug tree-optimization/39132] wrong code generated with -ftree-loop-disttribution

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2009-02-10 13:29 -------
I have a patch.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2009-02-10 13:15:51         |2009-02-10 13:29:52
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39132

[Bug tree-optimization/39132] wrong code generated with -ftree-loop-disttribution

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2009-02-10 14:54 -------
Subject: Bug 39132

Author: rguenth
Date: Tue Feb 10 14:54:13 2009
New Revision: 144060

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=144060
Log:
2009-02-10  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/39132
        * tree-loop-distribution.c (todo): New global var.
        (generate_memset_zero): Trigger TODO_rebuild_alias.
        (tree_loop_distribution): Return todo.

        * gcc.dg/torture/pr39132.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/torture/pr39132.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-loop-distribution.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39132

[Bug tree-optimization/39132] wrong code generated with -ftree-loop-disttribution

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2009-02-10 16:12 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39132

[Bug tree-optimization/39132] wrong code generated with -ftree-loop-disttribution

[kazu at gcc dot gnu dot org]

------- Comment #5 from kazu at gcc dot gnu dot org  2009-02-10 16:19 -------
Thanks, Richard!


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39132