help on understanding the code

[lpxz]

Dear all,
      I start to learn graal recently, as I found few documents publicly 
available, I send my questions here.
As for the CFG attached, i am curious about the following questions.
1) why the node "If" is often after a node "%", what functionality does 
the node "%" achieve?
2) what is the node "unsafeload"used  for, why is it always immediately 
after the startnode?
3) How is the framestate used?  I see the nodes "begin" and "endnode" in 
the CFG, does each pair delimit one framestate?

Thanks a lot for your help.

Regards
Peng