optimizing predictable branches on x86

[J.C. Pizarro]

It's a final summary for good performance of the tested machines:

  + unpredictable: * don't use conditional jmp (the worst).
 /                 * use cmov or C version.
/
\                 + no deps: * use cmov or C version.
 \               /
  + predictable: \
                  + has deps: * don't use cmov (the worst).
                              * use conditional jmp (the best).