Documentation about converting GIMPLE to LLVM IR in LLVM-GCC/DragonEgg

Dear All,

I am trying to understand the process followed for converting GIMPLE IR to LLVM IR in LLVM-GCC/DragonEgg - more importantly conversion of OpenMP extended GIMPLE IR to LLVM IR. It would be great if anybody points me to some documentation before I my-self delve into the understanding of related source code.