Re[2]: [fpc-devel] rtti, arrays and performance

[Michael Van Canneyt]

On Sat, 7 Oct 2006, Peter Vreman wrote:

> At 00:15 7-10-2006, you wrote:
> 
> 
> >-----Original Message-----
> >From: Michael Van Canneyt <michael at freepascal.org>
> >To: FPC developers' list <fpc-devel at lists.freepascal.org>
> >Date: Fri, 6 Oct 2006 22:01:55 +0200 (CEST)
> >Subject: Re: [fpc-devel] rtti, arrays and performance
> >
> >
> > > Did you see a change in performance ? Can you give an order of magnitude ?
> > >
> >
> >For me Shark profiler shows that 60%-70% of time spent in fpc_finalize (this
> >is on intel core duo, havn't measured on powerpc). After change it shown just
> >a few percents (I do not remember exactly, and it's a little bit hard to
> >measure exactly because this block is performd in a few seconds now). But
> >it's just a mine specific case. I use dynamic arrays heavily there, too much,
> >it would be better to use getmem there and then type cast it as pointer to
> >array. Generally speaking I think that it's not a significant optimization
> >for most of applications. Just it was easer for me to tweak rtl than to
> >change my code :). But anyway - if I have array of integer with a hundreds
> >thousand items call to finalize each item is not really good I think. What if
> >user has record with array inside, and that record has some dynamic variable?
> >as I understand fpc_finalize will try to finalize array too... And as I
> >understand dynamic arrays always finalizing their items.
> >
> > >
> > > I think it may be indeed a better idea to see whether the 
> > compiler can set a flag in the type info:
> > >
> > > If we change TTypeInfo to
> > >
> > >    TTypeInfo = record
> > >      Kind : TTypeKind;
> > >      Finalize : Boolean;
> > >      Name : ShortString;
> > >      // here the type data follows as TTypeData record
> > >    end;
> > >
> > > Then there is no need for a recursive loop (the compiler has 
> > already done that...);
> > > Only the Finalize field needs to be retrieved. Putting this field 
> > in the middle will
> > > make sure 99,9% of all existing code will still work.
> > >
> >
> >I don't know is this good - perhaps to not break other's code such attribute
> >can be placed before type info record (at offset -1 or -4 from typeinfo
> >pointer:)),so, if somebody relies on current typeinfo format his code will be
> >not broken?
> 
> If you relying on internal typeinfo your program already has a cross-platform
> issue. So this is not an issue that we change the internal structure. Adding
> the boolean is possible. But for the array finalize we also need an extra
> function that will check if the array needs finalization before entering the
> loop  that calls Finalize().

The TypeInfo of the array should also be checked, simply, no ?

Michael.