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[avr-gcc-list] Re: GCC-AVR Update (20082003)

From: Oleksandr Redchuk
Subject: [avr-gcc-list] Re: GCC-AVR Update (20082003)
Date: Tue, 26 Aug 2003 07:47:43 +0300 (EDT)

Hi, Theodore A. Roth!
25-Aug-03 10:11 you wrote:

KG>> ON my application, a USB HID device implemented in the AT43USB355, in IAR
KG>> it takes 12K, in avr-gcc, it takes 16K.
 Some my device, ported from MCS51 and KeilC51:
(size,8) optimisation: 9729 bytes

IAR C 1.40  (size,9)  11486
            (speed,9) 13189

AVRGCC 3.3 -O2        15040
+some options         14106

KG>> The difference is that IAR has "cross-call optimization".  What this does
KG>> is look for common code snippets.  If they're longer than 2-3 words (I'm
KeilC51 @ high degree of size optimization do the same.

TR> Just out of curiousity, what kind of performance hit do you take
TR> because of this? Every rcall/ret is going to cost you 7 clock cycles
Even without this "global common subexpression" optimisztion
size-optimized code slower than speed-optimised. But size
optimisation exist in most compilers, yes?
In many cases speed not critical, but code must fit into flash.

TR> Can you disable this optimization is speed critical code
TR> sections?
 This is command-line option -> can be controlled in
file-by-file basis. In old projects, compiled by IAR, I put ISR
and speed-critical code in separate files.

/* Oleksandr Redchuk, Brovary, Ukraine */
/* real '\x40' real '\x2E' kiev '\x2E' ua     */

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