Re: printing.el again

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

> Well, I think it's important to know the optimizations we can use or not
> and when.

I don't understand.  *You* can't use an optimization: the byte-compiler can.

> That is, if I have a code which test (featurep 'some-package) and
> some-package is not loaded, does the byte-compiler eliminate the code
> associated with this test?

Think of it this way: any optimization should be "semantics preserving" and
should thus only affect the CPU and memory usage but not the beavior.  So if
you can think of a case where an optimization induces a different behavior,
there are 3 possibilities:
1 - this case is really outlandish and can be itself considered a bug
    (e.g. someone does (provide 'xemacs)).
2 - the case is a real problem and thus the byte-compiler does not use this
    optimization.
3 - the case is a real problem but the compiler does use the optimization,
    in which case you have uncovered a byte-compiler bug and you should
    report it.


        Stefan