Libbeauty is an LLVM-based tool for decompiling x86_64 .o binary files and converting them into LLVM IR. While not yet implemented, it will then be possible to convert the LLVM IR back into C source code.
The aim of the libbeauty project is, "Given an input .o file, it can create a .c file that compiles and has the same function as the original .o file. This will later expand to handling binary files." Libbeauty also tries to automate as many tasks as possible.
Libbeauty can extract the entire instruction call flow in order to generate C code from the binary input file. However, work is still underway to identify loops and other program control flows.
For those wanting more information on this promising open-source LLVM-based decompiler and reverse engineering tool that's still under active development, check out the Libbeauty project page.