1- Add new instructions such as: clz, ctz, popcnt.
2
3- See if it is worth exporting mul2, mulu2, div2, divu2. 
4
5- Support of globals saved in fixed registers between TBs.
6
7Ideas:
8
9- Move the slow part of the qemu_ld/st ops after the end of the TB.
10
11- Change exception syntax to get closer to QOP system (exception
12  parameters given with a specific instruction).
13
14- Add float and vector support.
15