QBE is compiler backend that aims to provide 70% of the performance of industrial optimizing compilers in 10% of the code. QBE fosters language innovation by offering a compact user-friendly and performant backend. The size limit constrains QBE to focus on the essential and prevents embarking on a never-ending path of diminishing returns.
The C codebase of QBE is intended to remain hobby-scale and pleasant to hack on. Despite the small footprint, QBE provides a number of optimizations with good impact/weight ratio. It also facilitates integration with foreign systems by implementing the C ABI in full. This means that programs compiled by QBE can trivially call into C, and vice versa. The current version of QBE can target amd64 (linux and osx), arm64, and riscv64.
The backend that Cproc - small readable c compiler aims itself at. Seems like an attempt to do a simpler, smaller LLVM. Has simple IR example on the front page, which is nice.