I recently discovered a very useful Rust function: compiler_fence.

When performing code optimization, the compiler is unable to reorder memory reads and writes across a compiler fence. There are a variety of different exact fence types with different levels of restrictiveness regarding exactly what sorts of reordering can and can’t be done across them, but that’s the core principle: no reordering [of certain sorts] across this boundary.

Thus, when working with the highly inconvenient subset of code which works fine in debug mode but is nonfunctional in release mode due to compiler reordering, there’s no need for the sorts of awkward workarounds I was taught were necessary under equivalent circumstances in C, back when I was learning that. Instead, just add a compiler fence, and enjoy the lack of unwanted reordering with absolutely no overhead in unnecessary calculations!

Tags: Rust