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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/107051] redundant loads when copying a union
Date: Tue, 27 Sep 2022 13:18:17 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107051

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-09-27
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
With -O2 I see

func_1:
.LFB0:
        .cfi_startproc
        movl    e(%rip), %eax
        testl   %eax, %eax
        je      .L2
.L3:
        jmp     .L3
        .p2align 4,,10
        .p2align 3
.L2:
        movq    g_284+8(%rip), %rax
        movq    %rax, g_284(%rip)
        ret

note that with -O1 we retain

  c =3D g_284[1];
  c$f0_3 =3D g_284[1].f0;
  c.f0 =3D c$f0_3;
  g_284[0] =3D c;

after GIMPLE optimization which possibly explains this compared to

  c =3D g_284[1];
  g_284[0] =3D c;

with -O2.=