Hi all,
As a general head-up. I'm trying to fix a couple of these warnings in the AI
code right now. Most of it is just boring stuff. Ideal to fill a couple of
hours on a rainy monday afternoon.
Cheers,
Durk
On Mon, Sep 27, 2010 at 9:47 AM, James Turner <zakal...@mac.com> wrote:
>
> On 26 Sep 2010, at 22:09, ThorstenB wrote:
>
> > Hi,
> > there is a forum topic discussing compiler optimization to improve
> > frame rate ( http://www.flightgear.org/forums/viewtopic.php?f=45&p=96830
> > ).
> > I have also tried this (and successfully improved mine... :-) ).
> >
> > However, I also compiled with "-Wall" and this shows several issues
> > with the FlightGear sources. Simgear is really clean though (no
> > warnings with g++ 4.4, *clapclap*).
> >
> > I'm seeing 55 warnings with FlightGear: mainly (potential) usage of
> > uninitialized variables and violations of strict aliasing. The latter
> > easily results in broken code when optimizing with "-O2" or above (oh
> > no, "-O2" is the FlightGear default!). Well, and there is another 54
> > warnings in the AI module, but only since the member variables aren't
> > initialized in the sequence of their declaration (very easily fixed).
>
> In general, fixing warnings and switching on -Wall would get my vote;
> various people have done work on this over the past few years - Torsten
> Dryer and myself recently, but several others too. I'm not sure we can
> achieve the equivalent for all compilers, but requiring -Wall and possibly
> -Werror (optionally!) for GCC 4.4 would be nice. Patches welcome :)
>
> Regarding the compile flags, I'd prefer to use the default system CXXFLAGS
> by default, but provide a --aggressive or --optimised configure option that
> does this.
>
> Apple strongly recommend -Os over -O2 or -O3, as the default for production
> code, with -O2 or -O3 enabled on a file-by-file or module-by-module basis.
> This is really Apple saying they think i-cache coherency is a bigger win
> than massive loop unrolling, inlining and the like. They also recommend
> using profiling to identify the actual hot functions, since I'd guess the
> hot functions in the FlightGear frame loop are in OSG, not FlightGear
> itself. Even the FDMs aren't that hot, comparatively.
>
> If anyone could compare -Os with -O3 (with march=native and SSE enabled),
> and post the frame-rate difference, I'd be interested. (The comments above
> do date from the PPC days, some of which were i-cache starved)
>
> The SSE math flags are a no-brainer where supported - the -march-native and
> -sse flags are all Apple defaults in Xcode.
>
> James
>
>
>
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