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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/96271] Failure to optimize memcmp of doubles
 to avoid going through memory
Date: Wed, 22 Jul 2020 07:59:40 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96271

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|target                      |tree-optimization
   Last reconfirmed|                            |2020-07-22
     Ever confirmed|0                           |1

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note this could be folded on the GIMPLE level already similar to how we
inline string comparisons of size 1.  We should already fold this to
MEMCMP_EQ builtins and those can be inlined for bigger sizes, profitable
when we can emit a single load to a register for both values (thus
power-of-two size up to word_mode at least).  Desired gimple:

  _1 =3D VIEW_CONVERT <unsigned long> (a);
  _2 =3D VIEW_CONVERT <unsigned long> (b);
  _3 =3D _1 !=3D _2;
  return _3;

and memcmp of size 1 can be inlined as two char loads and subtraction.=