Newsgroups, off-topic

[Joseph Wakeling]

Steven Schveighoffer wrote:
> I did a little review of the code, I concur that the code is pretty
> identical, and the D version does not really do any extra allocation.  I
> found one place where you were using pow(x, 2) to square something in
> the D version but doing it with simple multiplication in the C++
> version, but that didn't account for any slowdowns when fixed.  I also
> saw some places where you write 0 to arrays several times, but removing
> those didn't help either.

Not several times superfluously?  I think I would be embarrassed if that
were true :-P

> I can only attribute the difference to g++'s more mature
> optimization/inlining techniques.  I can see why you are interested in
> having gdc working to try and compare the two :)

ldc already speeds things up somewhat (its inlining is better), but
still leaves a fairly sizeable gap.  There seem to be some fairly
sizeable performance differences between gcc and llvm:
http://www.phoronix.com/scan.php?page=article&item=apple_llvm_gcc&num=1

... which if I recall correctly was the motivation for the current gdc
team to start working on it again.

> In spite of all this, I still remain convinced that there is nothing
> inherently bad about these results, D compilers can and probably will
> get better at optimizing code.  That it doesn't beat a compiler which
> has been in production/mainstream for many more years probably shouldn't
> be surprising to any of us, even though we want D compilers to perform
> the best.

Completely agree here.  I was concerned based on early experience that I
was doing 'un-D-ish' things that were screwing performance, but now I'm
fairly confident that I can write OK D code.  From now on it will be all
pleasure as the compilers speed things up ... :-)

Thanks and best wishes,

    -- Joe