Optimize SEQV and SNEV

[numas13]

Elbrus-8C 1.2 GHz

$ luajit micro.lua 1.2 -b is..v
 frequency: 1.2
iterations: 10000
   repeats: 10
    filter: is..v

      c/i |    c/o | change | change | group                | description
----------|--------|--------|--------|----------------------|-------------
    486.2 |   24.3 |  -17.0 |   -41% | ISEQV                | num, taken
    305.2 |   15.3 |  -25.1 |   -62% | ISEQV                | num, not taken
    525.8 |   26.3 |  -21.0 |   -44% | ISEQV                | str, taken
    326.2 |   16.3 |  -33.0 |   -67% | ISEQV                | str, not taken
    525.8 |   26.3 |  -21.0 |   -44% | ISEQV                | tab, taken
    386.8 |   19.3 |  -33.0 |   -63% | ISEQV                | tab, not taken
    485.8 |   24.3 |  -16.1 |   -40% | ISNEV                | num, taken
    286.1 |   14.3 |  -25.1 |   -64% | ISNEV                | num, not taken
    545.9 |   27.3 |  -22.1 |   -45% | ISNEV                | str, taken
    306.1 |   15.3 |  -30.0 |   -66% | ISNEV                | str, not taken
    606.1 |   30.3 |  -22.1 |   -42% | ISNEV                | tab, taken
    306.2 |   15.3 |  -30.0 |   -66% | ISNEV                | tab, not taken

Benchmark           |    Old     New     Diff
--------------------|------------------------
array3d 300         |  28.07   27.65    1.52%
binary-trees 16     |  41.04   40.11    2.32% <<< ignore, unstable
chameneos 1e7       |  25.06   24.52    2.20%
coroutine-ring 2e7  |   8.69    8.09    7.42%
euler14-bit 2e7     |  82.95   82.72    0.28%
fannkuch 11         | 141.51  139.17    1.68%
fasta 25e6          |  74.15   73.40    1.02%
life                |   3.82    3.82    0.00%
mandelbrot 5000     |  71.72   69.74    2.84%
mandelbrot-bit 5000 | 162.84  160.41    1.51%
md5 20000           | 194.42  194.24    0.09%
nbody 5e6           |  40.29   40.27    0.05%
nsieve 12           |  38.13   38.29   -0.42%
nsieve-bit 12       |  90.01   89.68    0.37%
nsieve-bit-fp 12    |  71.12   69.87    1.79%
partialsums 1e7     |  10.01   10.01    0.00%
pidigits-nogmp 5000 |  60.44   59.63    1.36%
ray 9               |  54.04   53.63    0.76%
series 10000        |   6.71    6.70    0.15%
spectral-norm 3000  |  78.81   78.82   -0.01%