Well, it could "break" your code in that it might make your code produce differe...

lilyball on Oct 24, 2019 | parent | context | favorite | on: Rust and C++ on Floating-Point Intensive Code

Well, it could "break" your code in that it might make your code produce different results than a separate equivalent implementation that didn't use FMA.

Edit: Ok actually it sounds like it could literally break some algorithms, see https://news.ycombinator.com/item?id=21342974