AVR-Chat

--- Paul Curtis <plc@rowley.co.uk> wrote:

> Gcc generates this with -O3, an abomination in my
> eyes:

Larger numbers behind the -O option do not
automatically cause "better" optimization. There is no
universal definition for how to get "better" optimized
code (It depends on what the application is what is
you are trying to accomplish). With regards to
optimization.  anyway you look at it, it's a speed vs.
code size tradeoff.

With that said, In the example that you cited, using
-O3, gcc attempts to inline all "simple" functions.
So, you got what you asked for: A lot of inline
functions resulting in large code size. For the AVR
target, this normally constitutes a large 
pessimization due to the code increasement. However,
there are exceptions (But, your example is not one of
them...). 

So, to sum up your example, when you used the -O3
switch, you told gcc to include TONS of inline code.
gcc did exactly what you asked it to do: increase code
size.

To check my statements, query the internet for :

avr-libc-user-manual

and read the section of the manual on:

Selected general compiler options 



Regards

Marvin Dickens

=====
Registered Linux User No. 80253
If you use linux, get counted at: 
http://www.linuxcounter.org


	
		
__________________________________
Do you Yahoo!?
Yahoo! Photos: High-quality 4x6 digital prints for 25�
http://photos.yahoo.com/ph/print_splash