[Bug tree-optimization/56837] New: -ftree-loop-distribute-patterns generates incorrect code

[Bug tree-optimization/56837] New: -ftree-loop-distribute-patterns generates incorrect code

[pmblakely at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56837

             Bug #: 56837
           Summary: -ftree-loop-distribute-patterns generates incorrect
                    code
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: pmblakely@googlemail.com


Created attachment 29801
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29801
Compilation output from adding -v -save-temps

With gcc-4.8.0 release, and up to and including gcc-4.8-20130328,
-ftree-loop-distribute-patterns can give incorrect results:

Minimal test-case (named OptBug-4.8.C):

extern int __builtin_printf (__const char *__restrict __format, ...);

int main(void)
{
  bool* b = new bool[5];
  for(unsigned int i=0 ; i < 5 ; i++)
  {
    b[i] = true;
  }

  for(unsigned int i=0 ; i < 5 ; i++)
  {
    __builtin_printf("%d\n", b[i]);
  }

  return 0;
}

Compilation command: g++-4.8-20130328 OptBug-4.8.C -o OptBug-4.8 -O1
-ftree-loop-distribute-patterns

Expected output:
1
1
1
1
1

Actual output:
255
255
255
255
255

The expected output is produced if the -ftree-loop-distribute-patterns flag is
removed.
The incorrect behaviour is not exhibited by gcc-4.7.2.

[Bug tree-optimization/56837] -ftree-loop-distribute-patterns generates incorrect code

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56837

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
           Severity|major                       |normal

[Bug tree-optimization/56837] -ftree-loop-distribute-patterns generates incorrect code

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56837

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> 2013-04-04 07:57:14 UTC ---
That's because .ldist substitutes the first loop with __builtin_memset (b_7,
-1, 5);

[Bug tree-optimization/56837] -ftree-loop-distribute-patterns generates incorrect code

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56837

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2013-04-04
         AssignedTo|unassigned at gcc dot       |rguenth at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> 2013-04-04 07:58:19 UTC ---
Eh.  Mine.

[Bug tree-optimization/56837] -ftree-loop-distribute-patterns generates incorrect code

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56837

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> 2013-04-04 08:32:35 UTC ---
Testcase

extern "C" void abort (void);
extern "C" int memcmp (const void *, const void *, __SIZE_TYPE__);

bool b1[8];
bool b2[8] = { true, true, true, true, true, true, true, true };

int main()
{
  unsigned int i;
  for(i=0 ; i < 8; i++)
    b1[i] = true;

  if (memcmp (b1, b2, 8) != 0)
    abort ();

  return 0;
}

I have a patch.

[Bug tree-optimization/56837] -ftree-loop-distribute-patterns generates incorrect code

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56837

Richard Biener <rguenth at gcc dot gnu.org> changed:

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

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> 2013-04-04 11:01:51 UTC ---
Author: rguenth
Date: Thu Apr  4 10:55:25 2013
New Revision: 197476

URL: http://gcc.gnu.org/viewcvs?rev=197476&root=gcc&view=rev
Log:
2013-04-04  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/56837
    * tree-loop-distribution.c (classify_partition): For non-zero
    values require that the value has the same precision as its
    mode to be useful as memset value.

    * g++.dg/torture/pr56837.C: New testcase.

Added:
    trunk/gcc/testsuite/g++.dg/torture/pr56837.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-loop-distribution.c

Author: rguenth
Date: Thu Apr  4 11:00:45 2013
New Revision: 197477

URL: http://gcc.gnu.org/viewcvs?rev=197477&root=gcc&view=rev
Log:
2013-04-04  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/56837
    * tree-loop-distribution.c (classify_partition): For non-zero
    values require that the value has the same precision as its
    mode to be useful as memset value.

    * g++.dg/torture/pr56837.C: New testcase.

Added:
    branches/gcc-4_8-branch/gcc/testsuite/g++.dg/torture/pr56837.C
Modified:
    branches/gcc-4_8-branch/gcc/ChangeLog
    branches/gcc-4_8-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_8-branch/gcc/tree-loop-distribution.c