[Bug middle-end/23673] New: fold does not fold (a^b) != 0 to a != b

[Bug middle-end/23673] New: fold does not fold (a^b) != 0 to a != b

[pinskia at gcc dot gnu dot org]

These two functions should be the same on the tree level but are not:
int f(int a, int b)
{
  return (a^b) != 0;
}
int f1(int a, int b)
{
  return a != b;
}

They do result in the same asm though.

Another one from LLVM.

-- 
           Summary: fold does not fold (a^b) != 0 to a != b
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: missed-optimization, TREE
          Severity: enhancement
          Priority: P2
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23673

[Bug middle-end/23673] fold does not fold (a^b) != 0 to a != b

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-09-17 02:12 -------
Confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-09-17 02:12:09
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23673

[Bug middle-end/23673] fold does not fold (a^b) != 0 to a != b

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2005-11-30 16:44 -------
I am going to fix this one.


-- 

pinskia at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23673

[Bug middle-end/23673] fold does not fold (a^b) != 0 to a != b

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2005-12-02 03:17 -------
Hmm, this is getting harder (unless I just want to do (a^CST) == CST and (a^b)
== 0.  I am still deciding if I want to fix fold_binary from stoping from
returning a new tree if it does nothing except for switch the order of the
operands).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23673

[Bug middle-end/23673] fold does not fold (a^b) != 0 to a != b

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2005-12-02 18:12 -------
ok, I have a fix without rewritting some of fold_binary.  I just needed to
added a check for BIT_XOR_EXPR comming back, like invert_expr does.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23673

[Bug middle-end/23673] fold does not fold (a^b) != 0 to a != b

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2005-12-04 04:28 -------
I am no longer going to work on this, it is too much hasle to get this fixed.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|pinskia at gcc dot gnu dot  |unassigned at gcc dot gnu
                   |org                         |dot org
                URL|http://gcc.gnu.org/ml/gcc-  |
                   |patches/2005-               |
                   |12/msg00286.html            |
             Status|ASSIGNED                    |NEW
           Keywords|patch                       |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23673

[Bug middle-end/23673] fold does not fold (a^b) != 0 to a != b

[sayle at gcc dot gnu dot org]

------- Comment #6 from sayle at gcc dot gnu dot org  2006-02-25 22:27 -------
Subject: Bug 23673

Author: sayle
Date: Sat Feb 25 22:27:54 2006
New Revision: 111442

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=111442
Log:

        PR middle-end/23673
        * fold-const.c (fold_binary) <EQ_EXPR>:  Fold (X^Y) == 0 as X == Y
        and (X^Y) != 0 as X != Y.  Fold (X^Y) == Y as X == 0, and some
        symmetry related transformations.  Fold (X^C1) == C2 as
        X == (C1^C2).

        * gcc.dg/fold-eqxor-1.c: New test case.
        * gcc.dg/fold-eqxor-2.c: Likewise.
        * gcc.dg/fold-eqxor-3.c: Likewise.


Added:
    trunk/gcc/testsuite/gcc.dg/fold-eqxor-1.c
    trunk/gcc/testsuite/gcc.dg/fold-eqxor-2.c
    trunk/gcc/testsuite/gcc.dg/fold-eqxor-3.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/fold-const.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23673

[Bug middle-end/23673] fold does not fold (a^b) != 0 to a != b

[roger at eyesopen dot com]

------- Comment #7 from roger at eyesopen dot com  2006-02-25 23:36 -------
Fixed on mainline.


-- 

roger at eyesopen dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.2.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23673