[gergo_barany]

If this is one of the main things you want to demonstrate, wouldn't it be better to focus on this one goal first, instead of the whole pipeline from a C preprocessor to directly linked executables?

Essentially, if you say that LLVM's mid-end in particular is slow, I would expect you to present a drop-in replacement for LLVM's mid-end opt tool. You could leave C-to-LLVM-bitcode to Clang. You could leave LLVM-bitcode-to-machine-code to llc. Just like opt, take unoptimized LLVM bitcode as input and produce optimized LLVM bitcode as output. You would get a much fairer apples to apples comparison of both code quality and mid-end compiler speed (your website already mentions that you aren't measuring apples-to-apples times), and you would duplicate much less work.

Alternatively, look into existing Sea of Nodes compilers and see if you can build your demonstrator into them. LibFIRM is such a C compiler: https://libfirm.github.io/ There may be others.

It just seems like you are mixing two things: On the one hand, you are making some very concrete technical statements that integrated optimizations are good and the Sea of Nodes is a great way to get there. A credible demonstrator for this would be very welcome and of great interest to the wider compiler community. On the other hand, you are doing a rite-of-passage project of writing a self-hosting C compiler. I don't mean this unkindly, but that part is less interesting for anyone besides yourself.

EDIT: I also wanted to mention that the approach I suggest is exactly how LLVM became well-known and popular. It was not because of Clang; Clang did not even exist for the first eight years or so of LLVM's existence. Instead, LLVM focused on what it wanted to demonstrate: a different approach to mid-end optimizations compared to the state of the art at the time. Parsing C code was not part of that, so LLVM left that to an external component (which happened to be GCC).