Thorsten Froehlich <tho### [at] trfde> wrote:
> Nicolas Calimet wrote:
> >> The flag -mpowerpc64 is simply wrong in this context.
> >
> >
> >     Just a wild guess: Mac OS X 10.3 is not yet 64-bit, only the
> > next 10.4 version ("Tiger") is/will be?
>
> No, Mac OS X correctly handles 64-bit registers. Yet, changing a native data
> type has all kinds of implications one needs to consider.  One either knows
> how to track down the incompatibilities this might cause or one does not.
> If the later is the case, one should stay away from the option.  It would
> take ages to explain everything to a person asking why does compiler switch
> xyz not work as he/she expects.  Hence my recommendation to just not do
> something like that and use the default build.
>
>  Thorsten

I think the reason why the mpowerpc64 flag is not working is a gcc bug.
I've found some information about this on the web.
http://www.vtk.org/Bug/bug.php?op=show&bugid=491&pos=10

-mpowerpc should clearly work, according to the documentation. It is turned
on if you compile the code with -fast for example. -fast turns on different
optimization flags.
Apples benchmarks for the G5 were done with -fast.

In fact it is not mpowerpc64 which produces the runtime error, it is the
combination of -mpowerpc64 together with -fgcse. Both (and about 20 other
optimization flags are turned on with -fast). If you skip just -fsce and
leave mpowerpc64, the code runs ok.

Again, the flag -fast was introduced to get optimized performance on the G5.

And Thorsten, you do not have to explain me why '-mpowerpc64 is simply
'wrong in this context', but maybe you can just give me a reference to the
apple developer documentation for this.

The default build is optimized for the PPC7450 (G4), which in some aspects
is quite different to the G5. So it is natural trying to tune the
compilation
flags according to http://developer.apple.com/hardware/ve/g5.html.
For example the -mpowerpc-gpot enables the G5's hardware floating point
square root support.

There is nothing wrong about people are playing with this. This very
important in the open software community in order to improve software and
working out bugs.
Answers a la Thorsten however are not very constructive...

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