[Bug c/44858] New: likely integer wrong code bug

[Bug c/44858] New: likely integer wrong code bug

[regehr at cs dot utah dot edu]

regehr@john-home:~$ current-gcc -O0 small.c -o small
regehr@john-home:~$ ./small
checksum g_610 = 1
regehr@john-home:~$ current-gcc -O1 small.c -o small
regehr@john-home:~$ ./small
checksum g_610 = 0
regehr@john-home:~$ current-gcc -v
Using built-in specs.
COLLECT_GCC=current-gcc
COLLECT_LTO_WRAPPER=/home/regehr/z/compiler-install/gcc-r161813-install/libexec/gcc/i686-pc-linux-gnu/4.6.0/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: ../configure --with-libelf=/usr/local --enable-lto
--prefix=/home/regehr/z/compiler-install/gcc-r161813-install
--program-prefix=r161813- --enable-languages=c,c++
Thread model: posix
gcc version 4.6.0 20100704 (experimental) (GCC) 
regehr@john-home:~$ cat small.c
extern int printf (__const char *__restrict __format, ...);

int g_33 = 3;
int g_610 = 1;

long long foo(int i1, int i2)
{
    return (i1 / i2);
}

int main(void)
{
    int l_2 = 2;
    l_2 &= foo(1, g_610) > g_610;
    g_610 = (g_33 != 0) | l_2;
    printf("checksum g_610 = %d\n", g_610);
    return l_2;
}


-- 
           Summary: likely integer 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=44858

[Bug rtl-optimization/44858] likely integer wrong code bug

[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
          Component|c                           |rtl-optimization
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-07-08 08:14:08
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] likely integer wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #1 from jakub at gcc dot gnu dot org  2010-07-08 08:37 -------
Things go wrong in the combiner:

(insn 21 42 22 6 pr44858.c:16 (parallel [
            (set (reg/v:SI 62 [ c ])
                (and:SI (reg:SI 68)
                    (const_int 2 [0x2])))
            (clobber (reg:CC 17 flags))
        ]) 375 {*andsi_1} (expr_list:REG_DEAD (reg:SI 68)
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))

(insn 22 21 23 6 pr44858.c:17 (set (reg:CCZ 17 flags)
        (compare:CCZ (mem/c/i:SI (symbol_ref:SI ("a") [flags 0x2]  <var_decl
0x7f8d06f05000 a>) [0 a+0 S4 A32])
            (const_int 0 [0]))) 2 {*cmpsi_ccno_1} (nil))

(insn 23 22 24 6 pr44858.c:17 (set (reg:QI 70)
        (ne:QI (reg:CCZ 17 flags)
            (const_int 0 [0]))) 570 {*setcc_qi} (expr_list:REG_DEAD (reg:CCZ 17
flags)
        (nil)))

(insn 24 23 25 6 pr44858.c:17 (parallel [
            (set (reg:SI 69)
                (zero_extend:SI (reg:QI 70)))
            (clobber (reg:CC 17 flags))
        ]) 119 {*zero_extendqisi2_movzbl_and} (expr_list:REG_DEAD (reg:QI 70)
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))

(insn 25 24 26 6 pr44858.c:17 (parallel [
            (set (reg:SI 65 [ b.2 ])
                (ior:SI (reg/v:SI 62 [ c ])
                    (reg:SI 69)))
            (clobber (reg:CC 17 flags))
        ]) 394 {*iorsi_1} (expr_list:REG_DEAD (reg:SI 69)
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))

changes into:

(note 21 42 22 6 NOTE_INSN_DELETED)

(insn 22 21 23 6 pr44858.c:17 (set (reg:CCZ 17 flags)
        (compare:CCZ (mem/c/i:SI (symbol_ref:SI ("a") [flags 0x2]  <var_decl
0x7f8d06f05000 a>) [0 a+0 S4 A32])
            (const_int 0 [0]))) 2 {*cmpsi_ccno_1} (nil))

(note 23 22 24 6 NOTE_INSN_DELETED)

(insn 24 23 25 6 pr44858.c:17 (parallel [
            (set (reg/v:SI 62 [ c ])
                (and:SI (reg:SI 68)
                    (const_int 2 [0x2])))
            (clobber (reg:CC 17 flags))
        ]) 375 {*andsi_1} (expr_list:REG_UNUSED (reg:CC 17 flags)
        (expr_list:REG_DEAD (reg:SI 68)
            (nil))))

(insn 25 24 26 6 pr44858.c:17 (set (reg:SI 65 [ b.2 ])
        (ne:SI (reg:CCZ 17 flags)
            (const_int 0 [0]))) 569 {*setcc_si_1_movzbl} (expr_list:REG_DEAD
(reg:CC 17 flags)
        (nil)))


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] [4.5/4.6 Regression] likely integer wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #2 from jakub at gcc dot gnu dot org  2010-07-08 09:58 -------
Caused by http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=152642


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |uros at gcc dot gnu dot org
         AssignedTo|jakub at gcc dot gnu dot org|unassigned at gcc dot gnu
                   |                            |dot org
             Status|ASSIGNED                    |NEW
            Summary|likely integer wrong code   |[4.5/4.6 Regression] likely
                   |bug                         |integer wrong code bug


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] [4.5/4.6 Regression] likely integer wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #3 from jakub at gcc dot gnu dot org  2010-07-08 10:01 -------
Updated testcase:

extern void abort (void);
int a = 3;
int b = 1;

__attribute__((noinline)) long long
foo (int x, int y)
{
  return x / y;
}

__attribute__((noinline)) int
bar (void)
{
  int c = 2;
  c &= foo (1, b) > b;
  b = (a != 0) | c;
  return c;
}

int
main (void)
{
  if (bar () != 0 || b != 1)
    abort ();
  return 0;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] [4.5/4.6 Regression] likely integer wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #4 from jakub at gcc dot gnu dot org  2010-07-08 14:44 -------
Created an attachment (id=21147)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=21147&action=view)
gcc46-vrp.patch

So, combiner seems to be the first to notice that c must be actually zero
(2 & (x > y)).
This patch just tries to notice it earlier, during VRP, which of course isn't a
fix for this bug (which is somewhere in the combiner where it doesn't notice
that when it moves the and insn it clobbers cc which is needed), just makes it
latent for -O2 (still present at -O1 or -O2 -fno-tree-vrp).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] [4.5/4.6 Regression] likely integer wrong code bug

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.5.1
            Version|unknown                     |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] [4.5/4.6 Regression] likely integer wrong code bug

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] [4.5/4.6 Regression] likely integer wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #5 from jakub at gcc dot gnu dot org  2010-07-22 09:36 -------
The VRP changes have been committed, so on the trunk this will be now
reproduceable only with -O1 or -O2 -fno-tree-vrp.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] [4.5/4.6 Regression] likely integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2010-07-31 09:29 -------
GCC 4.5.1 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.5.1                       |4.5.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] [4.5/4.6 Regression] likely integer wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #7 from jakub at gcc dot gnu dot org  2010-08-25 13:25 -------
Created an attachment (id=21560)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=21560&action=view)
gcc46-pr44858.patch

The combiner bug seems to be similar to PR20322, attached untested patch should
fix it.


-- 

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|NEW                         |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] [4.5/4.6 Regression] likely integer wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #8 from jakub at gcc dot gnu dot org  2010-08-25 14:01 -------
Created an attachment (id=21561)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=21561&action=view)
gcc46-pr44858-2.patch

Alternate patch, which doesn't give up so easily (usually both sets can go in
any order, so if added clobbers prevent one order, this patch tries the other
order too and only gives up if both orders aren't going to work).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] [4.5/4.6 Regression] likely integer wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #9 from jakub at gcc dot gnu dot org  2010-08-25 17:51 -------
Subject: Bug 44858

Author: jakub
Date: Wed Aug 25 17:50:59 2010
New Revision: 163552

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=163552
Log:
        PR rtl-optimization/44858
        * combine.c (try_combine): If recog_for_combine added CLOBBERs to
        newi2pat, make sure they don't affect newpat.

        * gcc.c-torture/execute/pr44858.c: New test.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/pr44858.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/combine.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] [4.5/4.6 Regression] likely integer wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #10 from jakub at gcc dot gnu dot org  2010-08-25 21:25 -------
Subject: Bug 44858

Author: jakub
Date: Wed Aug 25 21:25:18 2010
New Revision: 163555

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=163555
Log:
        PR rtl-optimization/44858
        * combine.c (try_combine): If recog_for_combine added CLOBBERs to
        newi2pat, make sure they don't affect newpat.

        * gcc.c-torture/execute/pr44858.c: New test.

Added:
    branches/gcc-4_5-branch/gcc/testsuite/gcc.c-torture/execute/pr44858.c
Modified:
    branches/gcc-4_5-branch/gcc/ChangeLog
    branches/gcc-4_5-branch/gcc/combine.c
    branches/gcc-4_5-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858

[Bug rtl-optimization/44858] [4.5/4.6 Regression] likely integer wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #11 from jakub at gcc dot gnu dot org  2010-08-25 21:27 -------
Fixed.


-- 

jakub at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44858