Improving performance of rav1d video decoder

There's something about real optimization stories that I find fascinating – particularly the detailed ones including step-by-step improvements and profiling to show how numbers got better. In some way, they are satisfying to read.

Nicholas Nethercote's "How to speed up the Rust compiler" writings[1] fall into this same category for me.

Any others?

[1] https://nnethercote.github.io/