Simple question about how the optimizer works

[Robert Amesz]

Tim Roberts wrote:

> Kragen Sitaker <kragen at pobox.com> wrote:
> 
>>Simon Brunning <SBrunning at trisystems.co.uk> writes:
>>> I can't see how this optimisation could be automated - function
>>> f may or may not have side effects. 
>>
>>Checking whether f has side effects can be automated.
> 
> Can it?  Isn't that a variant of the Turing stopping problem?

Not really, because recursion - direct or indirect - can be detected, 
and that branch of the checking tree can be safely chopped off (you 
can't get _more_ potential side effects by calling the same function 
twice). The process is therefore guaranteed to terminate.


Robert Amesz