Re: Thoughts on getting correct line numbers in the byte compiler's warning messages

[Stefan Monnier]

> Looking at notes I made at the time, I amended a small portion of e.g.
> byte-optimize-body to make a new hash entry with the same value when a
> form was transformed.  The slowdown on just the byte optimiser was
> around a factor of three.

Ouch!

> I don't think I follow myself here.  I was thinking that accessing a
> hash table element was slow, therefore keeping a table value current and
> pushing transformed forms onto it would be faster than creating a new
> hash table entry for these new forms.

Ah, so you'd keep a pointer to the list somehow and add to it by
side-effects.  Yes, I guess it would indeed be noticeably faster for the
case of copying the location info from the source code to the
transformed code.

> Looking at the code for hash tables, the access time can not be all
> that long.

Hash-table accesses are pretty costly, in my experience.


        Stefan