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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/67962] Optimization opportunity with conditional swap to two MIN/MAX in phiopt
Date: Wed, 14 Oct 2015 11:44:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67962

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-10-14
          Component|c++                         |tree-optimization
            Summary|Optimization opportunity    |Optimization opportunity
                   |with conditional swap       |with conditional swap to
                   |                            |two MIN/MAX in phiopt
     Ever confirmed|0                           |1
           Severity|minor                       |enhancement

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
We miss the opportunity to turn

  <bb 2>:
  if (y_5(D) < x_6(D))
    goto <bb 4>;
  else
    goto <bb 3>;

  <bb 3>:

  <bb 4>:
  # y_4 = PHI <y_5(D)(3), x_6(D)(2)>
  # x_2 = PHI <x_6(D)(3), y_5(D)(2)>

into

   y_4 = MAX (x_6, y_5);
   x_2 = MIN (x_6, y_5);

and further optimize MINMAX (ISTR that was suggested elsewhere).  phiopt only
considers a single min/max operation.

Now the question is whether the transform would be profitable in isolation.