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From: "krebbel at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/108199] Bitfields and storage_order_attribute
Date: Thu, 22 Dec 2022 16:29:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108199

--- Comment #3 from Andreas Krebbel <krebbel at gcc dot gnu.org> ---
Moving the local definition of dst out of the function to global scope prev=
ents
the store from getting eliminated.

union DST dst;

As expected the store is still in the FRE dump:

  _1 =3D src_6(D)->a;
  dst.val =3D _1;                <---
  _2 =3D BIT_FIELD_REF <dst, 8, 0>;
  _3 =3D _2 & 64;
  if (_3 !=3D 0)
...

and the first by is accessed:

bar:
        movq    (%rdi), %rax
        movq    %rax, dst(%rip)
        testb   $64, %al
        jne     .L11=