[Nottingham] Compiler optimisation flags (gcc, g++)

Martin martin at ml1.co.uk
Wed Nov 5 01:10:32 GMT 2003

Robert Davies wrote:
> On Monday 03 Nov 2003 15:12, Martin wrote:
>>Any pitfalls with using the following compiler optimisations for an
>>Athlon Palomino cpu system?
> Theres' been a recent article in Gentoo news, comparing some optimisation 
> flags.  One of the issues was -O3 slowing code down (due to bloat), if you 
> want non-explicit function inlining then consider -finline-limit=N where N is 
> some size smaller than the default.  Altering alignments from defaults, also 
> did not help, except if made much larger.
> The problem with flags is, they are very processor and program specific, it's 

Ok folks,

Thanks for the feedback.

Links I've found useful are:


The exports script I'm now trying is:

# mlgccflags.sh 2003-10-17 M Lomas
# Set the default optimisation flags for gcc
# Full optimisations for the AthlonXP on gcc 3.2.2

export MACHTYPE="i686-mandrake-linux-gnu"
export HOSTTYPE="i686"
export CHOST="i686-pc-linux-gnu"
export CFLAGS="-march=athlon-xp -O3 -fexpensive-optimizations 
-funroll-loops -frerun-cse-after-loop -fr
erun-loop-opt -fomit-frame-pointer -fschedule-insns2 
-minline-all-stringops -mfancy-math-387 -mfp-ret-i
n-387 -m3dnow -msse -mfpmath=sse -mmmx -malign-double 
-falign-functions=4 -preferred-stack-boundary=4 -
fforce-addr -pipe"

(Beware the line breaks!)

A couple of very small test programs compile ok. I'll be trying bigger 
stuff over the coming days.

Be careful to use gcc/g++ as appropriate. I've lost an hour over very 
obscure linker problems due to using the wrong one... Duh!


Martin Lomas
martin at ml1.co.uk

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