Prefetching is tricky. I wouldn't try so many of them together. The number of outstanding requests is limited. How about this: 

// candidates for vectorization, lets break them apart
static inline void q7_to_m7(int m7[], int m6)
{
    int q, m6x = m6 ^ 1;
    for (q = 0; q < 128; q += 2) {      // unroll by 2
        m7[q] = (m6 ^ q) * H_PRIME;
        m7[q+1] = (m6x ^ q) * H_PRIME;
    }
}

static inline void prefetch_m(unsigned int i)
{
    _mm_prefetch(&bytevecM[i], _MM_HINT_T0);
    _mm_prefetch(&bytevecM[i^64], _MM_HINT_T0);
}

...
prefetch_m((m6^1) * H_PRIME);
int m7arr[130];
q7_to_m7(m7arr, m6);
// fixup for prefetching two iterations ahead
m7arr[129] = m7arr[128] = m7arr[127];
m7arr[13] = m7arr[15]; m7arr[10] = m7arr[12];

prefetch_m(m7arr[2]);
for (q7 = 1; q7 < 128; ++q7) {
    if (q7 == 10 || q7 == 13) continue;
    prefetch_m(m7arr[q7+2]);
    m7 = m7arr[q7];
    ...
}

[download]

In reply to Re^3: The 10**21 Problem (Part 3) by oiskuu
in thread The 10**21 Problem (Part 3) by eyepopslikeamosquito

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