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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/104582] [11/12 Regression] Unoptimal code for
 __negdi2 (and others) from libgcc2 due to unwanted vectorization
Date: Thu, 17 Feb 2022 16:35:57 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104582

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
What slp does is just
-  w.s.low =3D _1;
-  w.s.high =3D _5;
+  _14 =3D {_1, _5};
+  MEM[(union  *)&w] =3D _14;
I must say I don't really see that as a beneficial optimization, constructi=
on
of a vector from scalars just to store it in memory doesn't look ever like a
win.=