paperchalice wrote: Why we need this? We already have: https://github.com/llvm/llvm-project/blob/d5038b3774485d617e1300cf2f7b98c2460b9042/llvm/include/llvm/IR/PassManager.h#L210-L214 So the pipeline is still not nested. https://github.com/llvm/llvm-project/pull/128852