I have had code I wrote replaced by something that was 30% smaller, faster and more stable. It was a good and humbling experience.
I contributed an inliner to a language about ten years ago. Inlining is a problem that might seem easy at first, but for me it was like trying to restrain a rabid dog on a leash. I was pretty damn pleased with the end results and it served the language implentation well until about 2015. Then someone with an actual understanding of the problem worked on it for a week and produced something that I would describe as poetry.
I contributed an inliner to a language about ten years ago. Inlining is a problem that might seem easy at first, but for me it was like trying to restrain a rabid dog on a leash. I was pretty damn pleased with the end results and it served the language implentation well until about 2015. Then someone with an actual understanding of the problem worked on it for a week and produced something that I would describe as poetry.