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From: "unlvsur at live dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/111209] New: GCC fails to understand adc
 pattern
Date: Mon, 28 Aug 2023 06:47:25 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111209

            Bug ID: 111209
           Summary: GCC fails to understand adc pattern
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: unlvsur at live dot com
  Target Milestone: ---

Created attachment 55805
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D55805&action=3Dedit
bug example

template<typename T>
inline constexpr T addc(T a,T b,bool carryin,bool& carryout) noexcept
{
        T s;
        auto c1 =3D __builtin_add_overflow(a, b, __builtin_addressof(s));
        auto c2 =3D __builtin_add_overflow(s, carryin, __builtin_addressof(=
s));
        carryout =3D c1 | c2;
        return s;
}

void test_addc(unsigned long long* a,unsigned long long* b,unsigned long lo=
ng*
r)
{
    bool carry{};
    r[0]=3Daddc(a[0],b[0],carry,carry);
    r[1]=3Daddc(a[1],b[1],carry,carry);
}

I copied the example from gcc documentation

https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html

But gcc seems to fail to understand the pattern correctly even with what the
document describes.
gcc:
https://godbolt.org/z/Whaaahn41

clang:
https://godbolt.org/z/Ma6rvaYd6

Looks like a bug here.=