new optimizations for lunar - part1

[Auke Kok]

Zbigniew Łuszpiński wrote:

>Hi everyone
>
>I made patch for lunar tools which:
>* removes deprecated (for x86, x64 architecture only!), slowdown gcc option: 
>-mcpu=
>* adds new option -freorder-blocks
>
>Installation:
>Copy /var/lib/lunar to safe place (to have backup before patching)
>unpack newopti.diff.bz2 to /var/lib/
>go to /var/lib and execute: patch -p0 < newopti.diff
>
>After installation a new option will appear in Lunar Optimizations/Speed 
>optimizations: Blocks -freorder-blocks
>
>Additional information:
>This patch I use on my computer and it works. Do not know what happen on other 
>computers so be smart applying it.
>
>The -freorder-blocks function is rather safe optimization flag which is 
>enabled by default in -O2 and -O3 optimizations and disabled in -O0, -O1 and 
>-Os. If someone like me uses -Os optimization and want to get little speedup 
>can safely use -freorder-blocks. Compiled program can be little bigger than 
>-Os but smaller than -O2 and much smaller than -O3. This is good trade-off 
>(speed/size) in my opinion.
>
>-mcpu= makes code optimized for given processor but runable with 386. I think 
>that nobody needs such crazy optimization. The -march= option implies -mcpu=. 
>With gcc 3.4 you will even get ugly warning about deprecated -mcpu=.
>
>After throwing away -mcpu these options are useless:
>-mmmx, -msse, -msse2, -msse3, -m3dnow,
>the -march option implies them if specified CPU have support for them.
>The compilation process is little faster because gcc do not waste time 
>processing many commandline options.
>Refer to gcc manual, mailinglist for more information about gcc options.
>
>This is my first patch for lunar publicly available so feel free to post 
>comments.
>


Zbigniew,

thanks for your patch. I've quickly taken a look at it and have some 
comments with regard to your changes:

- -mcpu in lunar is set to the same architecture as -march, we do that 
so that no unoptimized i386 code is present in i686 optimized programs, 
so it makes sense to use -mcpu to 'remove compatibility code for slower 
cpus'.

-> however, I'll see if we can turn on/off the -mcpu option with a flag 
as to achieve downwards compatible code anyways, as this may be of use 
to people running the same binaries on multiple platforms.

- the sse/sse2/mmx flags are useful to people who wish to use mmx/sse 
with slower optimizations

- the '-freorder-blocks' looks interesting, however I don't think there 
are many people who use -Os or -O1 optimization right now, so the 
usability is low again. However for the ISO's it might be of use, or 
anyone who's experimenting with smaller but still optimized code.

In any case the -mcpu idea is interesting and I'll try to see if I can 
fit it in.

Thanks for your patch!

sofar