[LLVMdev] How to write a new backend?

[Vladimir Prus]

Hello,
I'm considering a possibility of writing an llvm backend for my research uses. 
Unfortunately, I can't find much information on how do to it. I more or less 
understood now the C backend is implemented, but for real backend I'd need at 
least register allocation. I beleive there's already register allocator in 
LLVM and I would like to reuse it if possible. 

The question is how? The REAME.txt in x86 directory does not tell that, and I 
see no other information.

In general, what's the best way to write a backend?

TIA,
Volodya