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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/102512] Redundant max/min operation before
 vector reduction
Date: Tue, 28 Sep 2021 09:07:21 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102512

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
  max_9 =3D *p_8(D);
  _10 =3D {max_9, max_9, max_9, max_9, max_9, max_9, max_9, max_9};
  vect__4.7_13 =3D MEM <vector(8) short int> [(short int *)p_8(D)];
  vect_max_11.8_14 =3D MAX_EXPR <_10, vect__4.7_13>;
  _20 =3D .REDUC_MAX (vect_max_11.8_14); [tail call]

it's a bit difficult to improve here - match.pd doesn't like MEMs too much
and this all just collapses because _10 is a splat of element zero of
vect__4.7_13 ...

In theory the vectorizer could use the first full vector as initial value
or of course a vector of all SHORT_MIN.  But the intent of using the first
scalar value was that this would optimize better ...=