Optimize load latency for "FORXXX" Opcode.

    FFT         2.18 -> 2.32
    SOR         5.49 -> 5.60
    MC          1.31 -> 1.33
    SPARSE      2.86 -> 2.96
    LU          4.18 -> 4.28

    OVERALL     3.23 -> 3.30  +2.17%
DUALNUM for minmax and a couple of load/store simplifications.

by this commit, our code is generally OK for returning to community for
further development.

SCI Bench
===
            LuaJIT   Lua
FFT         2.32     1.97   +17.77%
SOR         5.54     4.39   +26.20%
MC          1.32     1.38   -4.35%
SPARSE      2.95     3.09   -4.53%
LU          4.26     3.23   -31.89%

OVERALL     3.28     2.81   +16.73%

LuaJIT Bootstrap
===

LuaJIT    Lua
8.041s    9.312s  +15.81%