Optimizing g++ 3.2

Optimizing g++ 3.2

[Richard Guenther]

Hi!

How can I build an optimized g++ compiler, preferrably using profiling
feedback from heavily templated code? What are suggested options for
compiling gcc, if optimizing for speed? Will -fprefetch-loop-arrays help
(Athlon TB)? What are experiences?

What are suggested g++ options to speed up compilations of heavily
templated code during development?

Thanks for help, Richard.

--
Richard Guenther <richard.guenther@uni-tuebingen.de>
WWW: http://www.tat.physik.uni-tuebingen.de/~rguenth/
The GLAME Project: http://www.glame.de/

Re: Optimizing g++ 3.2

[Andreas Jaeger]

Richard Guenther <rguenth@tat.physik.uni-tuebingen.de> writes:

> Hi!
>
> How can I build an optimized g++ compiler, preferrably using profiling
> feedback from heavily templated code? What are suggested options for
> compiling gcc, if optimizing for speed? Will -fprefetch-loop-arrays help
> (Athlon TB)? What are experiences?

Depends on your code.  My page http://www.suse.de/~aj/SPEC has  a
comparison of some options - but that was done with an older compiler,

Andreas

> What are suggested g++ options to speed up compilations of heavily
> templated code during development?
>
> Thanks for help, Richard.

-- 
 Andreas Jaeger
  SuSE Labs aj@suse.de
   private aj@arthur.inka.de
    http://www.suse.de/~aj

Re: Optimizing g++ 3.2

[Joe Buck]

> How can I build an optimized g++ compiler, preferrably using profiling
> feedback from heavily templated code? What are suggested options for
> compiling gcc, if optimizing for speed? Will -fprefetch-loop-arrays help
> (Athlon TB)? What are experiences?

I haven't seen much on this.  I should warn, though, that if you do *any*
experiments of this kind there is a risk that the compiler you produce
will not be reliable (general rule of programming: if it has never been
tested, it probably does not work).  So, before you use your profiled
compiler built with a long list of specialized options, be sure that you
run the regression suite first and get the same results as you get with
a normal "make bootstrap-lean".  Otherwise you might just produce garbage
very quickly.

> What are suggested g++ options to speed up compilations of heavily
> templated code during development?

I'll let others give suggestions, but ...

Even on a single-processor machine, "make -j2" will give substantial
speedup, since one process can have the CPU while the other is doing disk
I/O, and C++ tends to need lots of disk I/O because of the large headers.
This assumes that you have enough RAM, of course.