bearophile wrote:
Walter Bright:
All compiler behavior is based on what the observer sees. If the
compiler can rearrange things in a manner that the observer cannot
detect, then the rearrangement is allowed.
OK. But if the language turns putting impure expressions inside a
function call into a compile time error, allowing only pure
expressions inside function calls, then the compiler can always be
free to rearrange those expressions, and there's both no performance
penalty and the programmer can be certain there is no performance
penalty. I guess you are not interested in this idea.
I agree I'm not interested in making impure expressions illegal.
But I was just pointing out that the compiler optimizer *already* relies
on knowing about side effects when reordering code. It's central to any
flow analysis optimization.
