Re: [Ocaml-lib-devel] ExtList: using _setcdr instead of Obj.magic

[Brian H. <bri...@ql...>]

On Mon, 21 Apr 2003, Nicolas Cannasse wrote:

> > Went through and changed all the inlined _setcdr calls to normal _setcdr
> > calls.
> 
> Uh ! it took me some time to inlined them :'(

Then I wish you had asked me before doing so.  As I'm opposed to it.

> 
> > a) If we never call the function, why define it?
> 
> It is called , it should actually be called when call - complexity is lower
> than O(n) since the overhead is not big.

Which is never in list functions, that I know about.

> 
> > b) function calls aren't that expensive.  And _setcdr is probably inlined
> > in most cases anyways.
> 
> In native code, there is no problem with it.
> In bytecode, the speedups are around 20% and since we're working an on
> Standard library, it would be good to provide efficient code to the
> community, don't you think ? That's why after lots of benchs and differents
> versions I ended up inlining the calls.

Hmm.  I'm less concerned about performance with bytecode.  Bluntly, if you 
want speed, go native.  If you're going bytecode, you're giving up a lot 
of speed anyways.  But I'm still surprised it's not inlined in the 
bytecode case as well.  Just to check- you did use -inline, right?

> 
> > c) In the future, when we have to change the magic incantation to make it
> > work, we only have to change it once, in _setcdr, and not all over.
> 
> We will never have to do so.

I've yet to hear this in a case where it turned out to be so.  And I 
notice the changes are sneaking out of ExtList- I note that Enum has an 
Obj.magic call which is effectively _setcdr.  On my to-do list was to take 
a long hard look at Enum.force to see if I could move that _setcdr back 
into ExtList where it belongs.

Brian