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Re: [avr-gcc-list] Gcc branches small comparison.

From: Curtis Maloney
Subject: Re: [avr-gcc-list] Gcc branches small comparison.
Date: Mon, 24 Jan 2005 16:44:08 +1100
User-agent: Mozilla Thunderbird 1.0 (Windows/20041206)

Bruce D. Lightner wrote:
Dmitry K. wrote:
Results are in form: prog_words + stack_bytes

-mmcu=atmega8 -Os -frename-registers
                3.2.3   3.3.5   3.4.3   4.0     4.0-nrr

bsearch          69+12   68+12   67+12   66+12   66+12
free             99+2    92+2    92+2    86+2    86+2
qsort           464+22  450+22  450+22  412+22  412+22

The results for 4.0 clearly suck! These are big differences for microcontrollers with very limited memory space. Can you explain what is going on?

Well, those 3, at least, have improved - qsort quite considerably. So, it's not all bad. I suspect part of the problem is in the migration to the new tree-ssa branch, and migrating all the old optimisations across. Also, there has been considerable noise on the gcc mailing list about "fixing" the register allocator code.

Or, am I being stupid assuming that things will *always* get better as time goes on?

Given the GCC people consider "substantial reduction in code quality" to be a regression, no, thinks ought to always get better. But sometimes they'll make sacrifices on the few for the good of the many...

Maybe things like "Moore's Law" are setting unrealistic expectations for those of us in this business. Is the Second Law of Thermodynamics affecting "gcc" development? Is ever increasing entropy is somehow negatively affecting "gcc" source code tree! :-)

I don't see what a law about the rate of increase in cost effective transistor densities has to do with this... although, perhaps it's all the result of some emergent complexity? ;)

Chin up - from what I've been reading on the gcc mailing list, there's good news on the way.

(And yes, I've been somewhat non-plussed by some of the code GCC is generating, ESPECIALLY with respect to longs).

Curtis Maloney.

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