[Bug tree-optimization/15757] New: Convert "If (a >= b) X else if (b <= a) Y" into "if (a >= b) X".

[Bug tree-optimization/15757] New: Convert "If (a >= b) X else if (b <= a) Y" into "if (a >= b) X".

[kazu at cs dot umass dot edu]

void bar1 (void);
void bar2 (void);

void
foo (unsigned int a, unsigned int b)
{
  if (a >= b)
    bar1 ();
  else if (b <= a)
    bar2 ();
}

The last tree-ssa form looks like so:

foo (a, b)
{
<bb 0>:
  if (a_1 >= b_2) goto <L0>; else goto <L1>;

<L0>:;
  bar1 () [tail call];
  goto <bb 4> (<L3>);

<L1>:;
  if (b_2 <= a_1) goto <L2>; else goto <L3>;

<L2>:;
  bar2 () [tail call];

<L3>:;
  return;

}

Note that the second "if" should go away completely as the two "if"s
are identical except the order of the variables appearing in the condition.

This actually occurs in alias.i.t50.tailc like so:

  if (T.1029_168 >= T.1030_170) goto <L6>; else goto <L2>;

<L2>:;
  if (T.1030_170 <= T.1029_168) goto <L3>; else goto <L4>;

If I have the identical conditions twice, including the order of the variables,
then the second "if" goes away as expected.

-- 
           Summary: Convert "If (a >= b) X else if (b <= a) Y" into "if (a
                    >= b) X".
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at cs dot umass dot edu
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15757

[Bug tree-optimization/15757] Convert "If (a >= b) X else if (b <= a) Y" into "if (a >= b) X".

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-06-01 11:20 -------
Confirmed.

Hmm, looks like jump threading needs a little improvement.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |law at gcc dot gnu dot org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2004-06-01 11:20:34
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15757

[Bug tree-optimization/15757] Convert "If (a >= b) X else if (b <= a) Y" into "if (a >= b) X".

[law at redhat dot com]

------- Additional Comments From law at redhat dot com  2004-06-05 20:22 -------
Subject: Re:  Convert "If (a >= b) X else if
	(b <= a) Y" into "if (a >= b) X".

On Tue, 2004-06-01 at 05:20, pinskia at gcc dot gnu dot org wrote:
> ------- Additional Comments From pinskia at gcc dot gnu dot org  2004-06-01 11:20 -------
> Confirmed.
> 
> Hmm, looks like jump threading needs a little improvement.
No.  More correctly, we do not canonicalize equivalent expressions.

What we're looking at is canonicalizing commutative operators and
conditionals so that given two SSA_NAMEs as operands, they will
be automatically ordered such that the lowest SSA_NAME_VERSION 
appears first.  Given an SSA_NAME and a constant, the SSA_NAME
should come first.

A prototype of this (of course) fixes this problem.  I'm still
evaluating that prototype.

jeff



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15757

[Bug tree-optimization/15757] Convert "If (a >= b) X else if (b <= a) Y" into "if (a >= b) X".

[law at gcc dot gnu dot org]

------- Additional Comments From law at gcc dot gnu dot org  2004-06-14 20:43 -------
*** Bug 15758 has been marked as a duplicate of this bug. ***

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15757

[Bug tree-optimization/15757] Convert "If (a >= b) X else if (b <= a) Y" into "if (a >= b) X".

[law at gcc dot gnu dot org]

------- Additional Comments From law at gcc dot gnu dot org  2004-06-16 05:08 -------
Should be fixed with today's checkin to canonicalize expressions in
get_expr_operands.

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15757

[Bug tree-optimization/15757] Convert "If (a >= b) X else if (b <= a) Y" into "if (a >= b) X".

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |3.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15757