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From: "monad at posteo dot net" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/104665] New: Failure to recognize memcpy
Date: Wed, 23 Feb 2022 16:50:07 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104665

            Bug ID: 104665
           Summary: Failure to recognize memcpy
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: monad at posteo dot net
  Target Milestone: ---

The following serialization code:

void serialize_le(std::byte* __restrict dst, const std::uint32_t* __restrict
src)
{
    for (int i =3D 0; i < 32; ++i, ++src)
    {
        *dst++ =3D static_cast<std::byte>((*src >>  0) & 0xff);
        *dst++ =3D static_cast<std::byte>((*src >>  8) & 0xff);
        *dst++ =3D static_cast<std::byte>((*src >> 16) & 0xff);
        *dst++ =3D static_cast<std::byte>((*src >> 24) & 0xff);
    }
}

is not recognized as just copying memory.
Both clang and gcc fail to optimize it properly, however gcc creates an
"interesting" mess.
Flags used are `-std=3Dc++17 -O3 -march=3Dhaswell`


<https://godbolt.org/z/GM8jqssYd>=