[Bug c/24716] New: Wrong code generated when optimising

[Bug c/24716] New: Wrong code generated when optimising

[schnetter at aei dot mpg dot de]

In a large application, a certain routine from the UMFPACK library is
miscompiled when -O is specified.  Without optimisation, the routine works
fine.  This triggers an assertion failure in the code.

I use gcc (GCC) 4.1.0 20051030 (experimental).  The problem can be reproduced
with the attached source files.  To see the error, compile them with

/gcc/bin/gcc -g -O -o umfpack-bug umfpack-call.c umf_analyze.i
umf_apply_order.i umf_order_front_tree.i umf_dump.i

When run, the executable aborts with an assertion failure:

/Users/eschnett/Calpha/arrangements/AEIThorns/AHFinderDirect/src/sparse-matrix/umfpack/umf_analyze.c:500:
failed assertion `parent == j+1'
Abort trap (core dumped)

To make the error go away, omit the "-O" option.  In this case, the executable
runs without producing any output.

The error seems to be the following.  The routine UMF_analyze contains a large
loop in which the local variable pdest is changed.  In the next iteration,
pdest is reset to the value it had before the loop.  This happens only for
local variables, not for static or global variables.

The error seems to be specific to powerpc; it does not happen on i386.

gcc 3.3 does not have this problem.


-- 
           Summary: Wrong code generated when optimising
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: schnetter at aei dot mpg dot de
 GCC build triplet: powerpc-apple-darwin8.2.0
  GCC host triplet: powerpc-apple-darwin8.2.0
GCC target triplet: powerpc-apple-darwin8.2.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug middle-end/24716] [4.1 Regression] Wrong code generated when optimising

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
            Summary|Wrong code generated when   |[4.1 Regression] Wrong code
                   |optimising                  |generated when optimising
   Target Milestone|---                         |4.1.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug middle-end/24716] [4.1 Regression] Wrong code generated when optimising

[schnetter at aei dot mpg dot de]

------- Comment #1 from schnetter at aei dot mpg dot de  2005-11-07 18:42 -------
Created an attachment (id=10165)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10165&action=view)
Tarball with source code demonstrating the problem


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug middle-end/24716] [4.1 Regression] Wrong code generated when optimising

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2005-11-07 18:49 -------
(In reply to comment #0)
> The error seems to be specific to powerpc; it does not happen on i386.
It does fail for me on i686 with 4.1.0 20051026.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug middle-end/24716] [4.1 Regression] Wrong code generated when optimising

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2005-11-07 20:39 -------
A little more info, umf_analyze.i is being miscompiled.  I don't know which one
yet.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug middle-end/24716] [4.1 Regression] Wrong code generated when optimising

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2005-11-07 20:43 -------
-O1 -fno-tree-ccp -fno-tree-store-ccp -fno-tree-dominator-opts works  (maybe
this will give a hint on how to reduce the issue).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug middle-end/24716] [4.1 Regression] Wrong code generated when optimising

[schnetter at aei dot mpg dot de]

------- Comment #5 from schnetter at aei dot mpg dot de  2005-11-08 15:54 -------
I would like to identify the cause of this problem.  Would it help if I tracked
down the patch number that caused this problem?  Andrew, do you have an
automated system to do that, or is someone already doing it?  Otherwise I would
try that with a small script.  But it seems to take a long time to do that, so
I wouldn't want to waste the effort.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug middle-end/24716] [4.1 Regression] Wrong code generated when optimising

[bonzini at gcc dot gnu dot org]

------- Comment #6 from bonzini at gcc dot gnu dot org  2005-11-08 17:47 -------
For now, I am trying to get the size of umf_analyze down by removing the
unnecessary prototypes, beautifying the code, etc...

Paolo


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug middle-end/24716] [4.1 Regression] Wrong code generated when optimising

[bonzini at gcc dot gnu dot org]

-- 

bonzini at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bonzini at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-11-09 08:20:55
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug middle-end/24716] [4.1 Regression] Wrong code generated when optimising

[bonzini at gcc dot gnu dot org]

------- Comment #7 from bonzini at gcc dot gnu dot org  2005-11-09 08:20 -------
Reduced testcase

/* { dg-do run } */
/* { dg-options "-O -fdump-tree-dom3" } */

int Link[] = { -1 };
int W[] = { 2 };

extern void abort (void);

int f (int k, int p)
{
  int pdest, j, D1361;
  j = 0;
  pdest = 0;
  for (;;) {
    if (pdest > 2)
      do
        j--, pdest++;
      while (j > 2);

    if (j == 1)
      break;

    while (pdest > p)
      if (j == p)
        pdest++;

    do
      {
        D1361 = W[k];
        do
          if (D1361 != 0)
            pdest = 1, W[k] = D1361 = 0;
        while (p < 1);
    } while (k > 0);

    do
      {
        p = 0;
        k = Link[k];
        while (p < j)
          if (k != -1)
            pdest++, p++;
      }
    while (k != -1);
    j = 1;
  }

  /* The correct return value should be pdest (1 in the call from main).
     DOM3 is mistaken and propagates a 0 here.  */
  return pdest;
}

int main ()
{
  if (!f (0, 2))
    abort ();
  return 0;
}

/* { dg-final { scan-tree-dump-times "return 0" 1 "dom3" } } */
/* { dg-final { cleanup-tree-dump "dom3" } } */


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug tree-optimization/24716] [4.1 Regression] Wrong code generated when optimising

[bonzini at gcc dot gnu dot org]

------- Comment #8 from bonzini at gcc dot gnu dot org  2005-11-09 08:22 -------
dom3 is at fault


-- 

bonzini at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|middle-end                  |tree-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug tree-optimization/24716] [4.1 Regression] Wrong code generated when optimising

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |law at gcc dot gnu dot org
           Severity|normal                      |critical
  GCC build triplet|powerpc-apple-darwin8.2.0   |
   GCC host triplet|powerpc-apple-darwin8.2.0   |
 GCC target triplet|powerpc-apple-darwin8.2.0   |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug tree-optimization/24716] [4.1 Regression] Wrong code generated when optimising

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2005-11-09 13:14 -------
It's IVCANONs fault, pr24716.c.t76.ivcanon:

...

  # pdest_23 = PHI <0(1)>;
<L24>:;
  return pdest_23;

}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug tree-optimization/24716] [4.1 Regression] Wrong code generated when optimising

[rguenth at gcc dot gnu dot org]

------- Comment #10 from rguenth at gcc dot gnu dot org  2005-11-09 13:31 -------
Or more definitely, store copyprop.

  # BLOCK 1 freq:122  
  # PRED: 0 [100.0%]  (fallthru,exec) 31 [100.0%]  (fallthru,exec)
  # jD.1285_18 = PHI <0(0), 1(31)>; 
  # pD.1281_7 = PHI <pD.1281_25(0), pD.1281_48(31)>;
  # kD.1280_5 = PHI <kD.1280_26(0), kD.1280_30(31)>;
  # WD.1277_1 = PHI <WD.1277_27(0), WD.1277_57(31)>;
<L0>:;
  if (0) goto <L43>; else goto <L3>;
  # SUCC: 2 [50.0%]  (true,exec) 6 [50.0%]  (false,exec)

...

  # BLOCK 6 freq:122 
  # PRED: 1 [50.0%]  (false,exec) 5 [100.0%]  (fallthru,exec)
  # jD.1285_20 = PHI <jD.1285_18(1), jD.1285_17(5)>;
  # pdestD.1284_11 = PHI <0(1), 1(5)>;
<L3>:;
  if (jD.1285_20 == 1) goto <L24>; else goto <L26>;
  # SUCC: 33 [10.0%]  (loop_exit,true,exec) 7 [90.0%]  (false,exec)

...

  # BLOCK 33 freq:12
  # PRED: 6 [10.0%]  (loop_exit,true,exec)
  # pdestD.1284_23 = PHI <pdestD.1284_11(6)>;
<L24>:;
  return pdestD.1284_23; 


cfg_cleanup will propagate through the PHIs.


-- 

rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug tree-optimization/24716] [4.1 Regression] Wrong code generated when optimising

[rguenth at gcc dot gnu dot org]

------- Comment #11 from rguenth at gcc dot gnu dot org  2005-11-09 13:59 -------
Doh, I have a fix.  What a stupid error in analyze_evolution_in_loop.


-- 

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|2005-11-09 08:20:55         |2005-11-09 13:59:19
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug tree-optimization/24716] [4.1 Regression] Wrong code generated when optimising

[rguenth at gcc dot gnu dot org]

------- Comment #12 from rguenth at gcc dot gnu dot org  2005-11-09 14:01 -------
Created an attachment (id=10185)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10185&action=view)
patch

this is what I'm going to test.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug tree-optimization/24716] [4.1 Regression] Wrong code generated when optimising

[pinskia at gcc dot gnu dot org]

------- Comment #13 from pinskia at gcc dot gnu dot org  2005-11-09 15:07 -------
(In reply to comment #10)
> Or more definitely, store copyprop.
s/store/scev/


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug tree-optimization/24716] [4.1 Regression] Wrong code generated when optimising

[rguenth at gcc dot gnu dot org]

------- Comment #14 from rguenth at gcc dot gnu dot org  2005-11-09 18:01 -------
Subject: Bug 24716

Author: rguenth
Date: Wed Nov  9 18:00:59 2005
New Revision: 106700

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=106700
Log:
2005-11-09  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/24716
        * tree-scalar-evolution.c (analyze_evolution_in_loop): Use
        t_bool to track results from follow_ssa_edge.

        * gcc.c-torture/execute/pr24716.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/pr24716.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-scalar-evolution.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716

[Bug tree-optimization/24716] [4.1 Regression] Wrong code generated when optimising

[rguenth at gcc dot gnu dot org]

------- Comment #15 from rguenth at gcc dot gnu dot org  2005-11-09 18:02 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24716