[Bug target/110979] Miss-optimization for O2 fully masked loop on floating point reduction.

[amonakov at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110979

--- Comment #2 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
Yes, it is wrong-code to full extent. To demonstrate, you can initialize 'sum'
and the array to negative zeroes:

#define FLT double
#define N 20

__attribute__((noipa))
FLT
foo3 (FLT *a)
{
    FLT sum = -0.0;
    for (int i = 0; i != N; i++)
      sum += a[i];
    return sum;
}

int main()
{
    FLT a[N];
    for (int i = 0; i != N; i++)
        a[i] = -0.0;
    if (!__builtin_signbit(foo3(a)))
        __builtin_abort();
}