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Re: [avr-gcc-list] Urgent Queries about AVR-GCC

From: Neil Johnson
Subject: Re: [avr-gcc-list] Urgent Queries about AVR-GCC
Date: Tue, 3 Jun 2003 21:28:38 +0100 (BST)

> I tracked down the reason, and it's the IAR optimization called
> "cross-call optimization".

More commonly known as tail-merging or cross-linking.  An early example of
code factoring that, as you have found, can make a big difference.  If
anyone's interested, AbsInt have developed a post-link tool called aiPop:


that does tail-merging and all sorts of other fun tricks.  So far they
have only developed a version for the Siemens C16x/ST10 micros (obviously
aiming for the automotive market ;-)

> I don't know how hard this would be to add, and I definitely don't know
> how to do it.  However, from my perspective it is "low-hanging fruit". (I
> need those 4K bytes.)

I guess one way to do it yourself is to pull out the common tails into
your own functions, and hope that GCC spots that you're doing a tail call
and converts the rcall/ret into an rjmp.

You could try it...it might work.


Neil Johnson :: Computer Laboratory :: University of Cambridge ::
http://www.njohnson.co.uk          http://www.cl.cam.ac.uk/~nej22
----  IEE Cambridge Branch: http://www.iee-cambridge.org.uk  ----

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