[Bug c++/28003] New: optimizer bug

[Bug c++/28003] New: optimizer bug

[rwgk at yahoo dot com]

I will attach a small reproducer.

/* Reproducer for optimizer bug in gcc svn trunk revision 114570
   (as checked out 2006_06_12_0834 PDT)

   To produce correct output:
     g++ -Wall -O0 gcc_trunk_2006_06_12_0834_fc5_x86_64.cpp
     ./a.out

   To see the bug:
     g++ -Wall -O1 gcc_trunk_2006_06_12_0834_fc5_x86_64.cpp
     ./a.out

   Note the difference in the last line of the output:
       Correct: 1 0 0
     Incorrect: 0 0 0

   The output is also incorrect for -O2 and -O3.

   The last line of the output is correct if compiled with:
     g++ -Wall -O1 -DBAD_WORKAROUND gcc_trunk_2006_06_12_0834_fc5_x86_64.cpp
     ./a.out

   Platform:
     Fedora Core release 5 (Bordeaux)
     Linux rosie.lbl.gov 2.6.15-1.2054_FC5 #1 SMP Tue Mar 14 15:48:20 EST 2006
x
86_64 x86_64 x86_64 GNU/Linux

     % g++ -v
     Using built-in specs.
     Target: x86_64-unknown-linux-gnu
     Configured with: /net/rosie/scratch1/rwgk/gcc_trunk/configure
--prefix=/usr
/local_cci/gcc_trunk_2006_06_12_0834_fc5_x86_64 --enable-languages=c,c++
     Thread model: posix
     gcc version 4.2.0 20060612 (experimental)
 */


-- 
           Summary: optimizer bug
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rwgk at yahoo dot com
 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=28003

[Bug c++/28003] optimizer bug

[rwgk at yahoo dot com]

------- Comment #1 from rwgk at yahoo dot com  2006-06-12 19:28 -------
Created an attachment (id=11656)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11656&action=view)
short reproducer


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2006-06-13 04:41 -------
Hmm, we get after dce, just:
  reduced_cell_two_folds[26] = {};

And DCE removes:
  this_616 = &reduced_cell_two_folds[26].u;
....
  #   SMT.68_1055 = V_MAY_DEF <SMT.68_1054>;
  this_616->elems[0] = 1;
  #   SMT.68_1056 = V_MAY_DEF <SMT.68_1055>;
  this_616->elems[1] = 0;
  #   SMT.68_1057 = V_MAY_DEF <SMT.68_1056>;
  this_616->elems[2] = 0;
...
  this_621 = &reduced_cell_two_folds[26].h;
...
  #   SMT.68_1058 = V_MAY_DEF <SMT.68_1057>;
  this_621->elems[0] = 2;
  #   SMT.68_1059 = V_MAY_DEF <SMT.68_1058>;
  this_621->elems[1] = 1;
  #   SMT.68_1060 = V_MAY_DEF <SMT.68_1059>;
  this_621->elems[2] = 1;


Which does not make sense.  Nothing is special in alias shows what is going
wrong.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
           Severity|normal                      |critical
          Component|c++                         |tree-optimization
           Keywords|                            |alias, wrong-code
            Summary|optimizer bug               |[4.2 Regression] optimizer
                   |                            |bug
   Target Milestone|---                         |4.2.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

Re: [Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[Daniel Berlin]

pinskia at gcc dot gnu dot org wrote:
> ------- Comment #2 from pinskia at gcc dot gnu dot org  2006-06-13 04:41 -------
> Hmm, we get after dce, just:
>   reduced_cell_two_folds[26] = {};
> 
> And DCE removes:
>   this_616 = &reduced_cell_two_folds[26].u;
> ....
>   #   SMT.68_1055 = V_MAY_DEF <SMT.68_1054>;
>   this_616->elems[0] = 1;
>   #   SMT.68_1056 = V_MAY_DEF <SMT.68_1055>;
>   this_616->elems[1] = 0;
>   #   SMT.68_1057 = V_MAY_DEF <SMT.68_1056>;
>   this_616->elems[2] = 0;
> ...
>   this_621 = &reduced_cell_two_folds[26].h;
> ...
>   #   SMT.68_1058 = V_MAY_DEF <SMT.68_1057>;
>   this_621->elems[0] = 2;
>   #   SMT.68_1059 = V_MAY_DEF <SMT.68_1058>;
>   this_621->elems[1] = 1;
>   #   SMT.68_1060 = V_MAY_DEF <SMT.68_1059>;
>   this_621->elems[2] = 1;
> 
> 
> Which does not make sense.  Nothing is special in alias shows what is going
> wrong.
> 
> 

The only thing i can think of is that SMT.68 is not marked global.
Is it?

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[reichelt at gcc dot gnu dot org]

------- Comment #3 from reichelt at gcc dot gnu dot org  2006-06-13 13:11 -------
Confirmed.

Shorter testcase (should return 0, but returns 1):

====================================================================
struct A
{
  int i, j[9];
  A() : i(1) { j[0]=j[1]=j[2]=j[3]=j[4]=j[5]=j[6]=j[7]=j[8]=0; }
};

struct B
{
  A a;
};

B b[] =
{
  {}, {}, {}, {}, {}, {}, {}, {}, {}, {},
  {}, {}, {}, {}, {}, {}, {}, {}, {}, {},
  {}, {}, {}, {}, {}
};

int main()
{
  return 1 - b[sizeof(b)/sizeof(B) - 1].a.i;
}
====================================================================


-- 

reichelt at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |reichelt at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |monitored
   Last reconfirmed|0000-00-00 00:00:00         |2006-06-13 13:11:58
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[dberlin at dberlin dot org]

------- Comment #4 from dberlin at gcc dot gnu dot org  2006-06-13 13:29 -------
Subject: Re:  [4.2 Regression] optimizer bug

pinskia at gcc dot gnu dot org wrote:
> ------- Comment #2 from pinskia at gcc dot gnu dot org  2006-06-13 04:41 -------
> Hmm, we get after dce, just:
>   reduced_cell_two_folds[26] = {};
> 
> And DCE removes:
>   this_616 = &reduced_cell_two_folds[26].u;
> ....
>   #   SMT.68_1055 = V_MAY_DEF <SMT.68_1054>;
>   this_616->elems[0] = 1;
>   #   SMT.68_1056 = V_MAY_DEF <SMT.68_1055>;
>   this_616->elems[1] = 0;
>   #   SMT.68_1057 = V_MAY_DEF <SMT.68_1056>;
>   this_616->elems[2] = 0;
> ...
>   this_621 = &reduced_cell_two_folds[26].h;
> ...
>   #   SMT.68_1058 = V_MAY_DEF <SMT.68_1057>;
>   this_621->elems[0] = 2;
>   #   SMT.68_1059 = V_MAY_DEF <SMT.68_1058>;
>   this_621->elems[1] = 1;
>   #   SMT.68_1060 = V_MAY_DEF <SMT.68_1059>;
>   this_621->elems[2] = 1;
> 
> 
> Which does not make sense.  Nothing is special in alias shows what is going
> wrong.
> 
> 

The only thing i can think of is that SMT.68 is not marked global.
Is it?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2006-06-13 14:26 -------
(In reply to comment #4)
> The only thing i can think of is that SMT.68 is not marked global.
> Is it?

Some how I missed that before:
SMT.68, UID 2839, struct reduced_cell_two_fold_info, is aliased, is addressable


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[dberlin at gcc dot gnu dot org]

------- Comment #6 from dberlin at gcc dot gnu dot org  2006-06-13 17:15 -------
So it should have been marked global, and should alias the global var, but
apparently the global var doesn't pop into it's alias set


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[pinskia at gcc dot gnu dot org]

------- Comment #7 from pinskia at gcc dot gnu dot org  2006-06-29 19:47 -------
This is target independent.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  GCC build triplet|x86_64-unknown-linux-gnu    |
   GCC host triplet|x86_64-unknown-linux-gnu    |
 GCC target triplet|x86_64-unknown-linux-gnu    |
   Last reconfirmed|2006-06-13 13:11:58         |2006-06-29 19:47:20
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[steven at gcc dot gnu dot org]

------- Comment #8 from steven at gcc dot gnu dot org  2006-07-20 21:29 -------
Could this be a dup of the now-fixed Bug 28410 ?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[reichelt at gcc dot gnu dot org]

------- Comment #9 from reichelt at gcc dot gnu dot org  2006-07-21 10:17 -------
> Could this be a dup of the now-fixed Bug 28410 ?

No, because this one is still present.
(Or the fix in PR 28410 is incomplete.)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[janis at gcc dot gnu dot org]

------- Comment #10 from janis at gcc dot gnu dot org  2006-08-08 15:51 -------
A regression hunt on powerpc-linux identified the following patch where the
testcase from comment #3 starts failing:

    http://gcc.gnu.org/viewcvs?view=rev&rev=109938

    r109938 | dberlin | 2006-01-19 01:42:48 +0000 (Thu, 19 Jan 2006)


-- 

janis at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[dberlin at gcc dot gnu dot org]

-- 

dberlin at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |dberlin at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2006-06-29 19:47:20         |2006-08-09 14:39:55
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[dberlin at gcc dot gnu dot org]

------- Comment #11 from dberlin at gcc dot gnu dot org  2006-08-21 02:16 -------
This is impressive.
We add b as a may alias to the SMT, then it disappears from the list before
call clobbering!


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[dberlin at gcc dot gnu dot org]

------- Comment #12 from dberlin at gcc dot gnu dot org  2006-08-22 14:04 -------
Subject: Bug 28003

Author: dberlin
Date: Tue Aug 22 14:04:16 2006
New Revision: 116323

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=116323
Log:
2006-08-22  Daniel Berlin  <dberlin@dberlin.org>

        PR tree-optimization/28003
        * tree-ssa-alias.c (compute_may_aliases): Compute call clobbered
        before grouping aliases.


Added:
    trunk/gcc/testsuite/g++.dg/tree-ssa/pr28003.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/tree-ssa-alias.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[dberlin at gcc dot gnu dot org]

------- Comment #14 from dberlin at gcc dot gnu dot org  2006-08-22 14:05 -------
Fixed


-- 

dberlin at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003

[Bug tree-optimization/28003] [4.2 Regression] optimizer bug

[dberlin at gcc dot gnu dot org]

------- Comment #13 from dberlin at gcc dot gnu dot org  2006-08-22 14:05 -------
Fixed


-- 

dberlin at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28003