[jacb]

> how well a compiler does is mostly dependent on how many of those transformations happen to apply to your program at hand

Right, there's an infinite number of distinct useful code optimizations, there's a cost to checking if any given optimization can be applied, and some optimizations have _massive_ costs for very rare and specific savings, so any given compiler is making a practical decision to include some optimizations and omit others. There was some discussion in the Rust community about LLVM having a period where they weren't tracking regressions in compile times - so "the perfect optimizing compiler" isn't really a coherent goal. But I still wonder how much faster Optimal Chromium would be. Just another interesting number I'll never know, I suppose.

> I think it's almost certainly not even in NP

Yeah, that was sloppy of me, I think this is undecidable by Rice's theorem. Nice catch!