[ekidd]

> Maybe it is just the LLVM backend. It still is slow.

It's a combination of two things, as far as I know.

1. The LLVM backend is slow.

2. The Rust frontend has historically abused the LLVM backend badly, by feeding it large amounts of barely optimized code. This is being worked on, but it's going to take a while.

[nialv7]

> 2. The Rust frontend has historically abused the LLVM backend badly, by feeding it large amounts of barely optimized code. This is being worked on, but it's going to take a while.

That's what I heard 2~3 years ago.

[steveklabnik]

Yes, it's taken a _long time_ to pay down the technical debt from writing a compiler in itself for years. A huge step forward for doing so landed fairly recently, MIR, so progress is being made. It's already resulted in significant improvements, and will lead to more in the future.