Godbolting the Benchmarks Game

03 Jan 2021 reported that Rust is now faster than C across the board. Why? Lack of a good standard library and cache alignment were my gut feelings.

First off, many of these codes don’t Godbolt due to crates. You would have to expand the Rust.

On the command line:

cargo rustc —-profile=check -- -Zunstable-options --pretty=expanded

But that only expands macros in local code, you still don’t get crate code expansion.

cargo install cargo-xbuild
rustup component add rust-src

This lets you get llvm-ir down to core libraries via setting up for cross-compilation, but it wasn’t working for me on aarch64 MacOS.

The play.rust-lang did work but the output was huge. It emits miri, llvm-ir, and x86_64. The source is here.

I think I will circle back after thinking about how to automate the comparison at the LLVM IR level. First many of the codes are using different algorithms, and more importantly different memory allocation/access patterns. To bring C up to C++/Rust performance using allocation pools etc seems critical. I also want to know the performance bump of profile guided optimization - and how those branch predicions can be baked in.