[msbarnett]

> What's the point of this though? Why are you letting programmers write non-functional code?

He just told you. Because the only way to prevent it in general is to solve the halting problem.

> When does the loop exactly terminate?

In the general case this is provably impossible to determine.

(all you're seeing here is that the compiler authors felt no need to add special case logic to handle "trivial" cases of the halting problem. If the compiler sees any expression in a loop test, it assumes the loop will halt some of the time)

[adamnemecek]

> He just told you. Because the only way to prevent it in general is to solve the halting problem.

I'm aware. I think that I might have misunderstood what the optimization really does.

[mnarayan01]

The idea (I assume) is to let compilers optimize away loops without determining that they terminate. I.e. the rule is more aimed at loops which would terminate, but this lets compilers avoid proving that they do in fact terminate.

[msbarnett]

Grandparent presented this as a "surprising optimization" but I'd argue it's exactly what you'd expect when a compiler sees while(expression) -- he just happened to pick a trivial expression.