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Subject: [Bug tree-optimization/14847] [tree-ssa] combine "if (a & 1) goto there" and "if (a & 4) goto there"
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From: "rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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------- Comment #4 from rguenth at gcc dot gnu dot org  2008-04-29 10:01 -------
The ifcombine pass would do this since 4.3.0 if there were not an extra
conversion
for a bittest of bit zero:

<bb 2>:
  a.0_2 = (int) a_1(D);
  D.1556_3 = a.0_2 & 1;
  if (D.1556_3 != 0)
    goto <bb 4> (heaven);
  else
    goto <bb 3>;

<bb 3>:
  D.1558_5 = a_1(D) & 4;
  if (D.1558_5 != 0)
    goto <bb 4> (heaven);
  else
    goto <bb 5>;

this is probably due to fold.  I will have a look.

For

void
foo (unsigned int a)
{
  if (a & 2)
    goto heaven;
  if (a & 4)
    goto heaven;
  return;

 heaven:
  bar ();
}

this is optimized to

optimizing bits or bits test to a_1(D) & T != 0
with temporary T = 4 | 2
Merging blocks 2 and 3
foo (unsigned int a)
{
  unsigned int D.1583;
  unsigned int D.1556;
  unsigned int D.1555;

<bb 2>:
  D.1555_2 = a_1(D) & 2;
  D.1556_3 = a_1(D) & 4;
  D.1583_5 = a_1(D) & 6;
  if (D.1583_5 != 0)
    goto <bb 3> (heaven);
  else
    goto <bb 4>;

Invalid sum of incoming frequencies 6100, should be 7231
heaven:;
  bar ();

<bb 4>:
Invalid sum of incoming frequencies 11131, should be 10000
  return;

}


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2006-02-05 21:36:17         |2008-04-29 10:01:23
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14847