I ran your code as is and it took 47 seconds, ten seconds slower. I then changed: 

_mm_prefetch(&bytevecM[i], _MM_HINT_T0);
_mm_prefetch(&bytevecM[i^64], _MM_HINT_T0);

[download]
back to my original: 
_mm_prefetch(&bytevecM[(unsigned int)(i) & 0xffffff80], _MM_HINT_T0);
_mm_prefetch(&bytevecM[64+((unsigned int)(i) & 0xffffff80)], _MM_HINT_
+T0);

[download]
and it ran in 38 seconds, only one second slower. Note that the &0xffffff80 aligns on a 64 byte boundary while ensuring we get the two 64 byte cache lines required for the inner loop.

I profiled with VTune and both my (37 second) and your (38 second) solution showed up as having two (seven second) hotspots -- presumably due to memory latency -- in the same places, namely here: 

; 100  :         UNROLL(q8)

0x1400028e0      Block 178:
0x1400028e0      mov eax, r9d                      7.217s
0x1400028e3      xor rax, rdi                      0.060s
0x1400028e6      movzx r10d, byte ptr [rax+rsi*1]  0.100s
0x1400028eb      test r10d, r10d                   2.508s
0x1400028ee      jz 0x140002a0b <Block 192>

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and here: 
; 99   :        for (q8 = 14; q8 < 128; ++q8) {

0x140002a0b     Block 192:
0x140002a0b     inc r9d                            7.008s
0x140002a0e     cmp r9d, 0x80                      0.690s
0x140002a15     jl 0x1400028e0 <Block 178>

[download]

In reply to Re^4: The 10**21 Problem (Part 3) by eyepopslikeamosquito
in thread The 10**21 Problem (Part 3) by eyepopslikeamosquito

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