[comex]

> However, the programmer failed to inform the compiler that the call to ereport(ERROR,...) does not return. This implies that the division will always execute.

I don’t think that’s correct. The compiler is allowed to assume that functions marked noreturn do not return, but it’s not allowed to assume that functions not marked noreturn do return. In other words, it’s not undefined behavior for a function to call abort(), enter an infinite loop, etc. instead of returning. It would be very strange if it were!

There’s a somewhat related spec clause that lets the compiler assume that certain types of loops will eventually terminate [1], but that doesn’t apply here. Therefore I think the mentioned compiler optimization is illegal. The issue was reported back in 2011; it would be interesting to see whether newer versions of GCC, or Clang, behave the same way.

[1] https://stackoverflow.com/questions/16436237/is-while1-undef...

[slaymaker1907]

An infinite loop with no side effects is undefined behavior.

[comex]

I didn't say no side effects. But even an infinite loop with no side effects is well-defined if the controlling expression is a constant expression; see the link in my previous post.

[dooglius]

That seems to be the conclusion of the mailing list thread as well, there was an initial bad gcc bug report that didn't understand the problem, seemingly no follow-up with a proper bug report.