2 ms·

This is the problem; every compiler outcome is a series of small logic inferences that are each justifiable by language definition, the program's structure, and

by titzer 4y ago

This is the problem; every compiler outcome is a series of small logic inferences that are each justifiable by language definition, the program's structure, and the target hardware. The nasal demons are emergent behavior. It'd be one thing if programs hitting UB just vanished in a puff of smoke without a trace, but they don't. They can keep on spazzing out literally forever and do I/O, spewing garbage to the outside world. UB cannot be contained even to the process at that point. I personally find that offensive and rude that tools get away with being so garbage that they can't even promise to help you crash and diagnose your own problems. One mistake and you invite the wrath of God!

nayuki 4y ago
> I personally find that offensive and rude that tools get away with being so garbage that they can't even promise to help you crash and diagnose your own problems. This is literally why newer languages like Java, JavaScript, Python, Go, Rust, etc. exist. With the hindsight of C and C++, they were designed to drastically reduce the types of UB. They guarantee that a compile-time or run-time diagnostic is produced when something bad happens (e.g. NullPointerException). They don't include silly rules like "not ending a file with newline is UB". They overflow numbers in a consistent way (even if it's not a way you like, at least you can reliably reproduce a problem). They guarantee the consistent execution of statements like "i = i++ + i++". And for all the flak that JavaScript gets about its confusing weak type coercions, at least they are coded in the spec and must be implemented in one way. But all of these languages are not C/C++ and not compatible with them.
- titzer 4y ago
  Yes, and my personal progression from C to C++ to Java and other languages led me to design Virgil so that it has no UB, has well-defined semantics, and yet crashes reliably on program logic bugs giving an exact stack traces, but unlike Java and JavaScript, compiles natively and has some systems features. Having well-defined semantics means that the chain of logic steps taken by the compiler in optimizing the program never introduces new behaviors; optimization is not observable.
galangalalgol 4y ago
It can get truly bizarre with multiple threads. Some other thread hits some UB and suddenly your code has garbage register states. I've had someone UB the fp register stack in another thread so that when I tried to use it, I got their values for a bit, and then NaN when it ran out. Static analysis had caught their mistake, and then a group of my peers looked at it and said it was a false warning leaving me to find it long afterwards... I don't work with them anymore, and my new project is using rust, but it doesn't really matter if people sign off on code reviews that have unsafe{doHorribleStuff()}

by titzer 4y ago

nayuki 4y ago

> I personally find that offensive and rude that tools get away with being so garbage that they can't even promise to help you crash and diagnose your own problems. This is literally why newer languages like Java, JavaScript, Python, Go, Rust, etc. exist. With the hindsight of C and C++, they were designed to drastically reduce the types of UB. They guarantee that a compile-time or run-time diagnostic is produced when something bad happens (e.g. NullPointerException). They don't include silly rules like "not ending a file with newline is UB". They overflow numbers in a consistent way (even if it's not a way you like, at least you can reliably reproduce a problem). They guarantee the consistent execution of statements like "i = i++ + i++". And for all the flak that JavaScript gets about its confusing weak type coercions, at least they are coded in the spec and must be implemented in one way. But all of these languages are not C/C++ and not compatible with them.

titzer 4y ago
Yes, and my personal progression from C to C++ to Java and other languages led me to design Virgil so that it has no UB, has well-defined semantics, and yet crashes reliably on program logic bugs giving an exact stack traces, but unlike Java and JavaScript, compiles natively and has some systems features. Having well-defined semantics means that the chain of logic steps taken by the compiler in optimizing the program never introduces new behaviors; optimization is not observable.

galangalalgol 4y ago

It can get truly bizarre with multiple threads. Some other thread hits some UB and suddenly your code has garbage register states. I've had someone UB the fp register stack in another thread so that when I tried to use it, I got their values for a bit, and then NaN when it ran out. Static analysis had caught their mistake, and then a group of my peers looked at it and said it was a false warning leaving me to find it long afterwards... I don't work with them anymore, and my new project is using rust, but it doesn't really matter if people sign off on code reviews that have unsafe{doHorribleStuff()}