Questions about where to find information on IPO state in GCC

[Nicholas Krause]

Greetings Richard,
After looking through the current work on multi-threading seems that we 
can scale
better with a workqueue strategy sharing and launching depending on how 
state is
shared between the GCC passes.
I'm not very familiar with all the details of how state is share in the 
GIMPLE,RTL or
SSA passes so I was wondering where to find information on this. The manual
only seems to mention the pass manager and its interactions with passes 
for running
them.

Thanks,
Nick