The code:

void testit()
{
    pragma(inline, false);
    short[4] arr = [-1, 6, 0, 4];
    long1 A = *cast(long1*)(arr.ptr);
    assert(_mm_extract_pi16(A, 0) == 65535); // Error here
}

struct short4
{
    short[4] array;
}

struct long1
{
    long[1] array;
}

int _mm_extract_pi16 (long1 a, int imm8)
{
    return cast(ushort)((cast(short4)a).array[imm8]);
}

The error is the optimizer incorrectly rewrites 65535 to be an unsigned short and then does a signed short comparison, which fails to match the left hand side which is a short. Should rewrite it as a short.
void main()
{
    testit();
}