On 12/27/10 6:17 PM, Stefan Monnier wrote:
>>>>> Actually, both Fcar and Fcdr can GC (by signalling an error which
>>>>> triggers the debugger).
>>>> But the debugger will not return.
>>> Oh, right,
>> Discussions like this worry me. What if the function is later changed to
>> call something that can GC? What if it's used in some new context? If
>> it's not utterly performance-critical code, isn't it better to be safe
>> than sorry and GCPRO anyway? It's not as if it's an expensive operation.
>> Premature optimization is the root of all evil, after all.
> 
> On most platforms, GCPRO is a no-op, and on those where it's not, it's
> never been a major performance issue, AFAIK.  The problem is just that
> it makes the code that much more verbose and painful to
> write/read/maintain.

Hrm. You learn something every day --- I thought Emacs was doing precise
GC the way it has since time immemorial. How much of a win was the
GC_MARK_STACK conservative scanning approach?