DeVault: Announcing the Hare programming language

DeVault: Announcing the Hare programming language

C has, since at least ANSI C89, had both undefined behaviour and implementation defined behaviour. Implementation defined behaviour is the stuff that's hardware-defined - for implementation defined behaviour, the compiler must tell you how it implements it (but can say things like "arithmetic overflow for 32 bit integers is defined by the behaviour of ADD EAX, EBX on your CPU, while for doubles, it's defined by the behaviour of FADD ST0, STi with truncation to 64 bit only happening if the compiler chooses to store the value to memory"), while for undefined behaviour, the compiler can do anything it likes.

The underlying "gotcha" with C for us older programmers is that optimizing compilers weren't very good until the late 1980s; before then, it was reasonable to model compilers as translating what I wrote 1:1 to a lower level language, then peephole optimizing that language, then repeating the process until the lower level language is machine code.

That's not how modern compilers work, however. They do much more sophisticated analyses to drive optimization, and can thus easily detect many more opportunities to optimize, but those analyses come up with results that are surprising if you're thinking in terms of peephole optimization.