[Bug c/41917] New: Strange athrithmetic result with -O3

[Bug c/41917] New: Strange athrithmetic result with -O3

[chenyang at cs dot utah dot edu]

Using r153799, the following program gives strange result with -O3.

yang@yang-working:~$ svngcc -O3 -o small small.c
yang@yang-working:~$ ./small 
g_64 = 0
yang@yang-working:~$ cat small.c
#include <stdio.h>

unsigned int g_64 = 1;

int
main (void)
{
  unsigned int *l_65 = &g_64;
  unsigned int x = 0xC7D24B5E;
  unsigned int y = *l_65 | -2;
  unsigned int m = (y == 0) ? x : (x % y);

  if (m != x)
    {
      g_64 = 0;
    }

  printf ("g_64 = %x\n", g_64);
  return 0;
}

yang@yang-working:~$ svngcc -v
Using built-in specs.
COLLECT_GCC=svngcc
COLLECT_LTO_WRAPPER=/home/yang/compilers/libexec/gcc/i686-pc-linux-gnu/4.5.0/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: ../configure --enable-lto --prefix=/home/yang/compilers
--program-prefix=svn --enable-languages=c,c++
--with-libelf=/home/yang/compilers : (reconfigured) ../configure --enable-lto
--prefix=/home/yang/compilers --program-prefix=svn
--with-libelf=/home/yang/compilers --enable-languages=c,lto,c++ --no-create
--no-recursion : (reconfigured) ../configure --enable-lto
--prefix=/home/yang/compilers --program-prefix=svn
--with-libelf=/home/yang/compilers --enable-languages=c,c++,lto --no-create
--no-recursion
Thread model: posix
gcc version 4.5.0 20091102 (experimental) (GCC)


-- 
           Summary: Strange athrithmetic result with -O3
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: chenyang 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=41917

[Bug c/41917] Strange athrithmetic result with -O3

[regehr at cs dot utah dot edu]

------- Comment #1 from regehr at cs dot utah dot edu  2009-11-02 21:56 -------
The problem also appears to exist in 4.4.1.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41917

[Bug c/41917] Strange athrithmetic result with -O3

[chenyang at cs dot utah dot edu]

------- Comment #2 from chenyang at cs dot utah dot edu  2009-11-02 22:24 -------
The expected result is:

g_64 = 1


-- 

chenyang at cs dot utah dot edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41917

[Bug c/41917] Strange athrithmetic result with -O3

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
                   |dot org                     |
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-11-02 22:36:29
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41917

[Bug rtl-optimization/41917] Strange athrithmetic result with -O3

[jakub at gcc dot gnu dot org]

------- Comment #3 from jakub at gcc dot gnu dot org  2009-11-03 22:36 -------
Subject: Bug 41917

Author: jakub
Date: Tue Nov  3 22:36:39 2009
New Revision: 153874

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=153874
Log:
        PR rtl-optimization/41917
        * rtlanal.c (num_sign_bit_copies1) <case UMOD>: If sign bit of second
        operand isn't known to be 0, return 1.

        * gcc.c-torture/execute/pr41917.c: New test.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/pr41917.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/rtlanal.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41917

[Bug rtl-optimization/41917] Strange athrithmetic result with -O3

[jakub at gcc dot gnu dot org]

------- Comment #4 from jakub at gcc dot gnu dot org  2009-11-03 22:40 -------
Subject: Bug 41917

Author: jakub
Date: Tue Nov  3 22:40:08 2009
New Revision: 153875

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=153875
Log:
        PR rtl-optimization/41917
        * rtlanal.c (num_sign_bit_copies1) <case UMOD>: If sign bit of second
        operand isn't known to be 0, return 1.

        * gcc.c-torture/execute/pr41917.c: New test.

Added:
    branches/gcc-4_4-branch/gcc/testsuite/gcc.c-torture/execute/pr41917.c
Modified:
    branches/gcc-4_4-branch/gcc/ChangeLog
    branches/gcc-4_4-branch/gcc/rtlanal.c
    branches/gcc-4_4-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41917

[Bug rtl-optimization/41917] Strange athrithmetic result with -O3

[mikpe at it dot uu dot se]

------- Comment #5 from mikpe at it dot uu dot se  2009-11-14 16:32 -------
This wrong-code bug also occurs with 4.3.4 on i686-linux, but not with 4.2.4 or
4.1.2, making it a regression. The patch for 4.4 applies cleanly to 4.3 and
fixes the bug there with no new regressions (I tested i686, powerpc64, and
arm).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41917

[Bug rtl-optimization/41917] Strange athrithmetic result with -O3

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41917

[Bug rtl-optimization/41917] [4.3 Regression] Strange athrithmetic result with -O3

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.3.4
      Known to work|                            |4.2.4 4.4.3 4.5.0
            Summary|Strange athrithmetic result |[4.3 Regression] Strange
                   |with -O3                    |athrithmetic result with -O3
   Target Milestone|---                         |4.3.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41917

[Bug rtl-optimization/41917] [4.3 Regression] Strange athrithmetic result with -O3

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|4.3.4                       |4.3.4 4.4.2
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41917

[Bug rtl-optimization/41917] [4.3 Regression] Strange athrithmetic result with -O3

[bonzini at gcc dot gnu dot org]

------- Comment #6 from bonzini at gnu dot org  2010-02-16 08:15 -------
Subject: Bug 41917

Author: bonzini
Date: Tue Feb 16 08:15:37 2010
New Revision: 156795

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=156795
Log:
PR rtl-optimization/41917

* rtlanal.c (num_sign_bit_copies1) <case UMOD>: If sign bit of second
operand isn't known to be 0, return 1.

testsuite:
* gcc.c-torture/execute/pr41917.c: New test.


Added:
    branches/gcc-4_3-branch/gcc/testsuite/gcc.c-torture/execute/pr41917.c
Modified:
    branches/gcc-4_3-branch/gcc/ChangeLog
    branches/gcc-4_3-branch/gcc/rtlanal.c
    branches/gcc-4_3-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41917

[Bug rtl-optimization/41917] [4.3 Regression] Strange athrithmetic result with -O3

[bonzini at gnu dot org]

------- Comment #7 from bonzini at gnu dot org  2010-02-16 08:16 -------
Committed the patch to 4.3 too


-- 

bonzini at gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
      Known to work|4.2.4 4.4.3 4.5.0           |4.2.4 4.3.5 4.4.3 4.5.0
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41917