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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/92645] Hand written vector code is 450 times
 slower when compiled with GCC compared to Clang
Date: Thu, 23 Apr 2020 13:26:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D92645

--- Comment #23 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the issue is we're both not doing enough and too much, the half way early
optimizations do confuse us later.  Another such opportunity would maybe
be:

   short unsigned int _950;
  _950 =3D BIT_FIELD_REF <_58, 16, 240>;
  _253 =3D (unsigned char) _950;

where this is the only use of _950.  It might be tempting to "optimize"
this into

  _253 =3D BIT_FIELD_REF <_58, 8, 240>;

forwprop does similar transforms for loads of complex and vector (though
the above is not a load but the transform would extend to loads as well).=