Not going to budge an inch, eh? It must be as good as it will ever get.
Not to mention the underlying insinuation, that the Rust compiler developers are dumb for not being able to get at the 80s compiler's level of speed -- since you don't seem to accept that this is a byproduct of the advanced optimizations and security guarantees they do.
Try to be scientific. If you've got a conjecture, test it and see if it holds water. One excuse was that C++ is only faster because people build C++ projects with separate compilation units. Well, you can compile a project in C++ with a single compilation unit, and it's not horribly slow. Now you need a new conjecture.
The type system is comparable to Standard ML from the 70s. The lifetime analysis is a solid improvement over mainstream languages, but I have a tough time believing it needs to be an order of magnitude slower than const correctness. The optimizations are on par with C++ and Fortran (mostly because they're leveraging the guts from an existing C++ compiler). SML, C++, and Fortran do not compile as slowly as Rust. There's probably another reason.
I don't think the Rust compiler developers are dumb, and I never said that. I think several of them are brilliant but young (and occasionally very arrogant).
Rust is so close to being a great replacement for C++. I read every one of these threads about new releases hoping they'll eventually fix the problems. Compilation speed and memory use are lesser issues, but they're still important, and things like incremental compilation dodge the issues instead of fixing them.
The type system of Rust goes significantly beyond that of Standard ML, because of traits/typeclasses among many other features. Also, Standard ML is usually not implemented with monomorphization, which affects compile time.
> Compilation speed and memory use are lesser issues, but they're still important, and things like incremental compilation dodge the issues instead of fixing them.
Incremental compilation is a way of addressing the compile time and memory usage issues. It's just not the way you seem to want them to be fixed. Nobody did incremental compilation for fun; it was done because without it we didn't believe we could reach our compiler performance goals.
Again, you're asking for a magic bullet, and I'm saying it's not likely that there is going to be one. If one existed, it probably would have been found already. There's lots of hard work that has been done, and lots of hard work ahead.
If I had to guess what the most important issue is, it's that idiomatic Rust generates a lot more LLVM IR than idiomatic C++ does, because it leans on abstractions for safety and developer ergonomics. Think about how many more closures Rust code uses, what for loops expand to, what pointer arithmetic compiles to (ptr::offset), etc...
> Incremental compilation is a way of addressing the compile time and memory usage issues. It's just not the way you seem to want them to be fixed. Nobody did incremental compilation for fun.
I'm well aware that my opinion doesn't matter, but I doubt incremental compilation will make any real strides towards making things as good as they could be. It sounds like the real problem is here:
> If I had to guess what the most important issue is, it's that idiomatic Rust generates a lot more LLVM IR than idiomatic C++ does
I suspect every single feature in idiomatic Rust has a one-to-one translation to some bit of C++ that isn't too horrible. You can do lambdas, iterators, generators, or whatever else it takes to do Rust style for loops and closures in C++, and it won't choke the compiler. So while I don't doubt rustc is generating a lot more IR, I doubt it needs to.
Maybe the MIR optimization pass will move in that direction.
I'm simply pushing back on the idea that there's some obvious low-hanging fruit that clang did that rustc didn't. Compiler performance has more or less much been the #1 goal for well over a year now. The Rust compiler team (which hasn't included me for years, by the way) is fantastic. We'd all like for there to be some magic bullet that makes the compiler faster, but at this point I don't believe it exists. It's hard work from here on out.
I didn't suggest low hanging fruit or a magic bullet. If anything, incremental compilation is being promoted as that kind of thing, and I just wanted call it into question.
It’s called incremental progress.
It's the cross-module optimizations that make the compiler slow. Those optimizations are in service of C++-inspired ideal of being able to use layers of abstraction to make your code cleaner, but having the compiler flatten them down so your program still runs fast.