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From: "piotrsiupa at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/90693] Missing popcount simplifications
Date: Sun, 07 Jan 2024 12:56:48 +0000
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X-Bugzilla-Component: tree-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D90693

--- Comment #11 from Piotr Siupa <piotrsiupa at gmail dot com> ---
Thanks! Now the generated assembly is one instruction shorter.

It works for:
bool foo(unsigned x)
{
    [[assume(x !=3D 0)]];
    return std::has_single_bit(x);
}
and for:
bool foo(unsigned x)
{
    if (x =3D=3D 0)
        std::unreachable();
    else
        return std::has_single_bit(x);
}

However, I've noticed that:
bool foo(unsigned x)
{
    if (x =3D=3D 0)
        return true;
    else
        return std::has_single_bit(x);
}
still uses (X ^ (X - 1)) > (X - 1).=