bug#12463: 24.2; pos-visible-in-window-p gets slower over time

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> >> Sorry, can't remember.  Probably because I generally prefer passing
>> >> arguments explicitly over passing them via dynamic binding.
>> > We have gobs of functions in Emacs that access global variables like
>> > Vdynamic_library_alist.  I don't think one more function will change
>> > anything.
>> The question is not "global or not" but "let-bound or not".
>> If it's generally accessed as a global var, that's perfectly fine.
>> If it's generally let-bound, I prefer an explicit argument.
> Sorry, I don't follow.  We are discussing C code, so how do you mean
> "let-bound"?  If you mean by using specbind, then no, it isn't
> let-bound, it's a global variable that always has the same value as it
> had when the last cons cell was added to it.

I'm saying: is the variable usually set once and left alone, or is it
usually let-bound around the call to the function that uses
the variable?

In the case of dynamic-library-alist it seems it's never let-bound, so
it's probably better to access it directly as a global var, rather than
pass it as a parameter.


        Stefan