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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/102971] GCC cannot understand >>32 pattern
Date: Wed, 27 Oct 2021 21:03:04 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102971

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
#include <cstdint>

std::uint64_t umul_naive(std::uint64_t a,std::uint64_t b,std::uint64_t& hig=
h)
noexcept
{
        std::uint32_t a0(static_cast<std::uint32_t>(a));
        std::uint32_t a1(static_cast<std::uint32_t>(a>>32));
        std::uint32_t b0(static_cast<std::uint32_t>(b));
        std::uint32_t b1(static_cast<std::uint32_t>(b>>32));
        std::uint64_t c00(static_cast<std::uint64_t>(a0)*b0);
        std::uint64_t c01(static_cast<std::uint64_t>(a0)*b1);
        std::uint64_t c10(static_cast<std::uint64_t>(a1)*b0);
        std::uint64_t c11(static_cast<std::uint64_t>(a1)*b1);

        std::uint64_t d0{static_cast<std::uint32_t>(c00)};
        std::uint64_t c00_high{c00>>32};
        std::uint64_t c01_low{static_cast<std::uint32_t>(c01)};
        std::uint64_t c01_high{c01>>32};
        std::uint64_t c10_low{static_cast<std::uint32_t>(c10)};
        std::uint64_t c10_high{c10>>32};

        std::uint64_t d1{c00_high+c01_low+c10_low};
        std::uint64_t d2{(d1>>32)+c10_high+c01_high};
        std::uint64_t d3{(d2>>32)+c11};
        high=3Dd2|(d3<<32);
        return d0|(d1<<32);
}=