Chez Scheme essentially follows this rule, and has since its inception, and it is an incredibly impressive project IMO. It can compile itself in just a few seco

Chez Scheme essentially follows this rule, and has since its inception, and it is an incredibly impressive project IMO. It can compile itself in just a few seconds and has a fairly simple architecture (despite having 30+ distinct IR languages in the compilation pipeline, and Scheme being a relatively high level language already, on a ~100k(?) codebase) and it has very good overall performance for generated code that "scales well". It tries not to be too good at the expense of other things, or bad/unwieldly in others. The goal is more that "results are predictable and not fragile", but in practice it means you apply rules like this. It's like putting a monetary budget on feature creep, to me. Chez is a very pleasurable Scheme to work with. Apparently the only time they really violated this rule was when rearchitecting their compiler from using 5-6 distinct IR languages to over 30 of them using the "Nanopass" approach. So I assume the compile time simply went from "a few seconds" to "a few more seconds", but that's probably OK to do once over ~30 years, I guess. :) I was told once (by one of the developers of) the Microsoft C# compiler team followed a similar rule where they never made a release that regressed their internal compiler benchmarks, i.e. they were only allowed to get faster. Obviously the .NET runtime does a huge amount of heavy lifting in terms of a C# programs performance, making the compiler a bit simpler, but it still means things like optimizations must pay off in speed and effectiveness. They even rewrote the compiler from C++ to C# at one point and still met this goal somehow, apparently, and once you're at that point -- bootstrapping yourself -- you begin the virtuous cycle of self-improvement. I'd be interested to know if any C# developers have seen the Microsoft .NET compiler get slower -- everything I've heard is that it's very fast and nice to use.