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Here is the source code:

https://github.com/google/souper

The paper mentions that Souper links against LLVM 3.9, but a recent commit on GitHub states that dependencies have been bumped to LLVM 5.0, the most recent version.

The Souper source has been available and Regehr has posted on his Embedded in Academia blog several times about Souper.

https://blog.regehr.org/archives/1192

https://blog.regehr.org/archives/1252

But then a paper is a whole nuther thing.

Just by reading the HN title I was 90% sure this had to be John Regehr. The man’s a monster!
The abstract is not very clear, if you ask me. I would have expected at least an indication of the usefulness of this optimizer in terms of resulting speed, or an indication of how far we are from using this technique in production settings.
If we can automatically derive compiler optimizations, we might be able to sidestep some of the substantial engineering challenges involved in creating and maintaining a high-quality compiler

I think it's clear, but you may have assumed it's about something it's not? It's about saving effort in writing an optimizing compiler. Have you ever looked at how many and how big LLVM's optimization passes are?

The automatically derived passes may not result in code that's as fast as the hand-written passes. I assume they would have mentioned that if it were the case. But they take less effort to develop.

The article contains…

An Souper-optimized Clang-3.9 binary is almost 3 MB (4.4%) smaller than one built without Souper, though it is also about 2% slower.

It sounds like the perceived value is more about finding clever optimization patterns and explaining them to the Clang and Visual C++ developers for them to integrate.

Score one for me misreading titles again. I was looking forward to finding out what a Soup Optimizer could do for me. Sounds life-changing.