LLVM 2.0 and integer signedness

Hello everyone!

I'm using llvm for instrumenting code, and I need to know if there's a way to
difference between signed and unsigned Values of integer type during an
optimization pass. I know in llvm 1 it was possible, but i'd like to work
with llvm 2. Maybe using the debugging information? Is it available during
an optimization pass? How do I access it?

Thanks in advance