* Add optimizations related to caller/callee saved registers, thread synchronization and disable tier 0
* Refactoring
* Add a config entry to enable or disable the reg load/store opt.
* Remove unnecessary register state stores for calls when the callee is know
* Rename IoType to VarType
* Enable tier 0 while fixing some perf issues related to tier 0
* Small tweak -- Compile before adding to the cache, to avoid lags
* Add required config entry
