[Rd] request: allow inline functions in R

[Prof Brian Ripley]

BTW, I've just checked a hunch. I did not believe R_IsNaNorNA is actually
used in base R on a system with IEEE arithmetic (and I removed it to test
that).  That suggests you have not actually tested inlining it and your 
analysis is seriously flawed.

(Note to Deepayan: it is not a documented entry point, so please use 
ISNAN as documented.)

On Fri, 14 May 2004, Prof Brian Ripley wrote:

> On Fri, 14 May 2004, Li Long wrote:
> 
> > Hi, R core developers,

And BTW, R-devel is not the address of the core developers.

> > I work in the Swiss Institute of Bioinformatics.  We have two clusters of
> > Intel Itanium2 clusters for bioinformaticians to crank their data.  One
> > piece of software they use heavily is R and BioConductors.  I ported the R
> > codes and R packages to this platform already, and am working on
> > optimizing their performance.  I'm using Intel C/C++ compiler on this
> > platform running Linux.  One of my findings is that turning some functions
> > in R to "inline" functions boost performance significantly.
> > 
> > While R follows strict C89 standard right now, there're quite some good
> > reasons to relax the rule somewhat.  From my experience in software
> > development in industry, I understand very well both the portability issue
> > and backward compatability issue, I also see the hidden cost of holding
> > back for too long and not fully achieving the potential of new technology,
> 
> Could you then please quantify that hidden cost?
> 
> > I recommend that we allow "inline" functions in R's C codes.
> 
> In what sense do `we' not allow it?  And who is `we'?
> 
> The problem is that very few compilers fully support C99, and others have
> different ways to indicate inlining.  So a configure test is needed. I am
> sure that if you provide one together with patches to parts of the code
> where you find inlining beneficial, the real `we' would consider it
> carefully.  Especially if the `hidden cost' is noticeable.
> 
> ....
> 
> > In R, there are quite some simple functions that are called extremely
> > often, such as "R_IsNaNorNA", "R_finite", etc.  They are used in heavy
> > loops quite a lot.  They disrupt the pipelining, and negatively affect the
> > performance of the software.  For instance, on IA64, system call of
> > "isnan" cost 4 cycles, while a wrapper like "R_IsNaNorNA" could cost
> > several times more.
> 
> However, one of the motivations of eliminating support for non-IEEE-754
> platforms in R 2.0.0 is to enable some of this baggage to be eliminated.  
> But the wrapper is there for a good reason: to get the right answer.
> 
> Since I gather you have suitably modified code, it would be helpful to 
> your case to provide data 
> 
>  - on real problems
>  - on a mainstream platform.
> 
> of the actual performance impact of not inlining.
> 
> 

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595