[Bug c/43560] New: possible wrong code bug

[Bug c/43560] New: possible wrong code bug

[regehr at cs dot utah dot edu]

I don't believe the program below should crash when run.

Valgrind says the store at line 20 is at fault, which is strange since it looks
like the "if" branch should execute twice and the "else" branch 0 times.

regehr@john-home:~$ current-gcc -O small.c -o small
regehr@john-home:~$ ./small
Segmentation fault
regehr@john-home:~$ cat small.c
#include <stdio.h>

int g_6[1][2] = {{1,1}};
int g_34 = 0;
int *const g_82 = &g_6[0][1];
int *g_85[2][1] = {{&g_34}, {&g_34}};

void func_4 (void)
{
  int i;
  for (i = 0; i <= 1; i++) {
    if (g_6[0][1]) {
      *g_82 = 1;
    } else {
      int **l_109 = &g_85[1][0];
      if (&g_82 != l_109) {
      } else {
        *l_109 = &g_6[0][1];
      }
      *g_82 = 1;
    }
  }
}

int main (void)
{
  func_4();
  return 0;
} 

regehr@john-home:~$ current-gcc -v
Using built-in specs.
COLLECT_GCC=current-gcc
COLLECT_LTO_WRAPPER=/home/regehr/z/compiler-install/gcc-r157783-install/libexec/gcc/i686-pc-linux-gnu/4.5.0/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: ../configure --with-libelf=/usr/local --enable-lto
--prefix=/home/regehr/z/compiler-install/gcc-r157783-install
--program-prefix=r157783- --enable-languages=c,c++
Thread model: posix
gcc version 4.5.0 20100328 (experimental) (GCC)


-- 
           Summary: possible wrong code bug
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: regehr at cs dot utah dot edu
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

[Bug c/43560] possible wrong code bug

[sezeroz at gmail dot com]

------- Comment #1 from sezeroz at gmail dot com  2010-03-28 20:12 -------
Happens on x86_64-pc-linux-gnu, too. Segfaults with gcc-4.3.0 and 4.3.2 (as
shipped by fedora), but runs fine with 3.3.6, 3.4.6 and my custom 4.4.4.


-- 

sezeroz at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sezeroz at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

[Bug c/43560] possible wrong code bug

[hjl dot tools at gmail dot com]

------- Comment #2 from hjl dot tools at gmail dot com  2010-03-29 02:49 -------
It is caused by revision 147083:

http://gcc.gnu.org/ml/gcc-cvs/2009-05/msg00057.html


-- 

hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-03-29 02:49:04
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

[Bug c/43560] [4.5 Regession] possible wrong code bug

[hjl dot tools at gmail dot com]

-- 

hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.5.0
      Known to work|                            |4.4.3
            Summary|possible wrong code bug     |[4.5 Regession] possible
                   |                            |wrong code bug
   Target Milestone|---                         |4.5.0
            Version|unknown                     |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

[Bug tree-optimization/43560] [4.3/4.4 Regression] possible wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #12 from jakub at gcc dot gnu dot org  2010-04-08 11:31 -------
Subject: Bug 43560

Author: jakub
Date: Thu Apr  8 11:31:00 2010
New Revision: 158119

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=158119
Log:
        Backport from mainline:
        2010-03-29  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/43560
        * tree-ssa-loop-im.c (ref_always_accessed_p): Add store_p
        parameter.
        (can_sm_ref_p): Treat stores to readonly locations as
        trapping.

        * gcc.dg/torture/pr43560.c: New testcase.

Added:
    branches/gcc-4_4-branch/gcc/testsuite/gcc.dg/torture/pr43560.c
Modified:
    branches/gcc-4_4-branch/gcc/ChangeLog
    branches/gcc-4_4-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_4-branch/gcc/tree-ssa-loop-im.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

[Bug tree-optimization/43560] [4.3 Regression] possible wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #13 from jakub at gcc dot gnu dot org  2010-04-08 11:35 -------
Fixed also for 4.4.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|3.4.6 4.5.0                 |3.4.6 4.5.0 4.4.4
            Summary|[4.3/4.4 Regression]        |[4.3 Regression] possible
                   |possible wrong code bug     |wrong code bug


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

[Bug tree-optimization/43560] [4.3 Regression] possible wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #14 from jakub at gcc dot gnu dot org  2010-04-09 18:24 -------
Testcase distilled from OO.o that has been also fixed by this bugfix (failed at
-Os).  Do we want it for the testsuite too?

struct S
{
  int a, b;
  char c[10];
};

__attribute__((noinline)) void
test (struct S *x)
{
  while (x->b > 1 && x->c[x->b - 1] == '/')
    {
      x->b--;
      x->c[x->b] = '\0';
    }
}

const struct S s = { 0, 0, "" };

int
main ()
{
  struct S *p;
  asm ("" : "=r" (p) : "0" (&s));
  test (p);
  return 0;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

[Bug tree-optimization/43560] [4.3 Regression] possible wrong code bug

[rguenther at suse dot de]

------- Comment #15 from rguenther at suse dot de  2010-04-11 18:08 -------
Subject: Re:  [4.3 Regression] possible wrong
 code bug

On Fri, 9 Apr 2010, jakub at gcc dot gnu dot org wrote:

> ------- Comment #14 from jakub at gcc dot gnu dot org  2010-04-09 18:24 -------
> Testcase distilled from OO.o that has been also fixed by this bugfix (failed at
> -Os).  Do we want it for the testsuite too?
> 
> struct S
> {
>   int a, b;
>   char c[10];
> };
> 
> __attribute__((noinline)) void
> test (struct S *x)
> {
>   while (x->b > 1 && x->c[x->b - 1] == '/')
>     {
>       x->b--;
>       x->c[x->b] = '\0';
>     }
> }
> 
> const struct S s = { 0, 0, "" };
> 
> int
> main ()
> {
>   struct S *p;
>   asm ("" : "=r" (p) : "0" (&s));
>   test (p);
>   return 0;
> }

Yes please.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

[Bug tree-optimization/43560] [4.3 Regression] possible wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #16 from jakub at gcc dot gnu dot org  2010-04-12 10:18 -------
Subject: Bug 43560

Author: jakub
Date: Mon Apr 12 10:18:39 2010
New Revision: 158220

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=158220
Log:
        PR tree-optimization/43560
        * gcc.c-torture/execute/pr43560.c: New test.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/pr43560.c
Modified:
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

[Bug tree-optimization/43560] [4.3 Regression] possible wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #17 from jakub at gcc dot gnu dot org  2010-04-12 10:22 -------
Subject: Bug 43560

Author: jakub
Date: Mon Apr 12 10:22:21 2010
New Revision: 158221

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=158221
Log:
        PR tree-optimization/43560
        * gcc.c-torture/execute/pr43560.c: New test.

Added:
    branches/gcc-4_5-branch/gcc/testsuite/gcc.c-torture/execute/pr43560.c
Modified:
    branches/gcc-4_5-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

[Bug tree-optimization/43560] [4.3 Regression] possible wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #18 from jakub at gcc dot gnu dot org  2010-04-12 10:25 -------
Subject: Bug 43560

Author: jakub
Date: Mon Apr 12 10:25:11 2010
New Revision: 158222

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=158222
Log:
        PR tree-optimization/43560
        * gcc.c-torture/execute/pr43560.c: New test.

Added:
    branches/gcc-4_4-branch/gcc/testsuite/gcc.c-torture/execute/pr43560.c
Modified:
    branches/gcc-4_4-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

[Bug tree-optimization/43560] [4.3 Regression] possible wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #19 from rguenth at gcc dot gnu dot org  2010-05-22 18:13 -------
GCC 4.3.5 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.5                       |4.3.6


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

[Bug tree-optimization/43560] [4.3 Regression] possible wrong code bug

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43560

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|                            |
         Resolution|                            |FIXED
   Target Milestone|4.3.6                       |4.4.4
      Known to fail|                            |

--- Comment #20 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-06-27 11:58:39 UTC ---
Fixed for 4.4.4.