[anotherhue]

Yeah I've heard this my whole career, and while it sounds great it's been long enough that we'd be able to list some major examples by now.

What are the real world chances that a) one's compiled code benefits strongly from runtime data flow analysis AND b) no one did that analysis at the compilation stage?

Some sort of crazy off label use is the only situation I think qualifies and that's not enough.

[IggleSniggle]

Compiled Lua vs LuaJIT is a major example imho, but maybe it's not especially pertinent given the looseness of the Lua language. I do think it demonstrates that the concept that it is possible to have a tighter type-system at runtime than at compile time (that can in turn result in real performant benefits) is a sound concept, however.

[drysart]

The major Javascript engines already have the concept of a type system that applies at runtime. Their JITs will learn the 'shapes' of objects that commonly go through hot-path functions and will JIT against those with appropriate bailout paths to slower dynamic implementations in case a value with an unexpected 'shape' ends up being used instead.

There's a lot of lore you pick up with Javascript when you start getting into serious optimization with it; and one of the first things you learn in that area is to avoid changing the shapes of your objects because it invalidates JIT assumptions and results in your code running slower -- even though it's 100% valid Javascript.