BTW they've been on by default only since around 2010. IIRC Adacore checked the performance impact on most of their codebases and didn't really see an impact on performance (probably around the time branch prediction really improved on x86 and the Core architecture made branch misses far less painful).

They also pioneered validity checks injected by the compiler.

For the brave souls, shameless plug, I talk a bit about Ada's runtime checks, there https://blog.adacore.com/running-american-fuzzy-lop-on-your-...