[Bug c/17169] New: optimization bug

[Bug c/17169] New: optimization bug

[kminola at eng dot umd dot edu]

/* gcc-3.4.1 optimization bug

  gcc -o foo foo.c -O0 ok
  gcc -o foo foo.c -O1 bug

% ./config.guess
ia64-unknown-linux-gnu
%
% gcc -v
Reading specs from /u/kminola/public/gcc-3.4.1/ia64-Linux/bin/../lib/gcc/ia64-un
known-linux-gnu/3.4.1/specs
Configured with: /u/kminola/public/gcc-3.4.1/src/gcc-3.4.1/configure --enable-la
nguages=c --prefix=/u/kminola/public/gcc-3.4.1/ia64-Linux
Thread model: posix
gcc version 3.4.1
%

does NOT exist in gcc-3.5-20040711 */

#include <stdio.h>

#define GMP_RNDU 2
#define GMP_RNDD 3

int
bar (long a, int rnd_mode)
{
  int signx;
  long b;

  b = a >> 31;
  if (b) {
    signx = -1;
  } else { 
    signx = 1;
  } 

  if (signx < 0 && rnd_mode == GMP_RNDD)
  {
    return -1;
  }
  if (signx > 0 && rnd_mode == GMP_RNDU)
  {
    return 1;
  }
  return 2;
}

int
main (int argc, char *argv[])
{
  int val;
  long a;

  a = 1;
  val = bar (a, GMP_RNDU);
  if (val == 2) {
    printf("bug!\n");
  } else {
    printf("ok!\n");
  }

  return 0;
}

-- 
           Summary: optimization bug
           Product: gcc
           Version: 3.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kminola at eng dot umd dot edu
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: ia64-unknown-linux-gnu
  GCC host triplet: ia64-unknown-linux-gnu
GCC target triplet: ia64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17169

[Bug rtl-optimization/17169] optimization bug

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c                           |rtl-optimization
           Keywords|                            |wrong-code
      Known to work|                            |3.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17169

[Bug rtl-optimization/17169] optimization bug

[wilson at gcc dot gnu dot org]

------- Additional Comments From wilson at gcc dot gnu dot org  2004-08-26 02:03 -------
Appears to be a problem in combine.  We have 3 possible return values before
combine, but only two possible return values after combine.  I haven't traced
through combine far enough yet to determine what the problem is.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2004-08-26 02:03:30
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17169

[Bug rtl-optimization/17169] optimization bug

[sje at cup dot hp dot com]

------- Additional Comments From sje at cup dot hp dot com  2005-01-10 23:43 -------
I looked into this bug some, it is fixed on 4.0, but the patch that fixes it is
the integration of tree-ssa into the mainline.  I believe that the underlying
combine bug still exists but the tree-ssa changes result in different RTL being
generated so that the combine bug isn't hit.  I looked at try_combine using the
3.4 sources.  Attached is  the i1, i2, i3 values we enter try_combine with and
what it generates.  I have no idea how it came up with the result that it did
but that seems to be the heart of the problem.


In try_combine:

I1 is
(nil)
I2 is
(insn 53 51 54 2 (set (reg:BI 360)
        (eq:BI (reg/v:SI 341 [ rnd_mode ])
            (const_int 2 [0x2]))) 209 {*cmpsi_normal} (nil)
    (expr_list:REG_DEAD (reg/v:SI 341 [ rnd_mode ])
        (nil)))
I3 is
(insn 57 56 58 2 (set (reg:BI 363)
        (and:BI (gt:BI (reg/v:SI 342 [ signx ])
                (const_int 0 [0x0]))
            (reg:BI 360))) 66 {*cmpsi_and_1} (insn_list 53 (nil))
    (expr_list:REG_DEAD (reg/v:SI 342 [ signx ])
        (expr_list:REG_DEAD (reg:BI 360)
            (nil))))
==========================
Returns:

(insn 57 56 58 2 (set (reg:BI 363)
        (const_int 0 [0x0])) 1 {movbi} (nil)
    (nil))
==========================

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sje at cup dot hp dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17169

[Bug rtl-optimization/17169] optimization bug

[ebotcazou at gcc dot gnu dot org]

------- Comment #3 from ebotcazou at gcc dot gnu dot org  2007-05-17 15:17 -------
3.4.x is not maintained anymore.


-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebotcazou at gcc dot gnu dot
                   |                            |org
             Status|NEW                         |RESOLVED
         Resolution|                            |WONTFIX


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17169