Are the Rust benchmarks better because of Rust or because the Rust packages are just better written?
Surely the latter. Most of Rust's optimization comes from LLVM, so clang and others get the same benefit.
It could also be that Rust exposes more information that can be used to optimize the code it generates to LLVM. Its explicitness makes for a very complete depiction of dependencies and side effects.
That's interesting and makes sense. I had always thought of LLVM as being lossy when compiling anything more explicit than C++, but that's obviously nonsense since there are front-ends for things like Haskell. Cool!