Re: -O3 vs. -Os
Re: -O3 vs. -Os
- Subject: Re: -O3 vs. -Os
- From: Steve Checkoway <email@hidden>
- Date: Tue, 17 Jan 2006 11:39:52 -0800
On Jan 17, 2006, at 4:49 AM, Rustam Muginov wrote:
On Jan 17, 2006, at 12:06 PM, Steve Checkoway wrote:
How about a game? Still, I would say that this uses fairly
computationally intensive mathematics. Matrix multiplications left
and right for graphics work, resampling sounds for audio output,
etc. I have used Shark and there is no single hot spot clearly
visible in the game.
Do you using MacOS X audio resampler or your own?
Resampling, if it has to be performed with high quality, is a heavy
computation task.
the same question form matrix math - is it "in-game" code or code
from Accelerate.framework?
Resampling is performed via our own resampler. (I haven't gotten
around to using OS X's yet.) Matrix math, on the other hand uses
Accelerate as it was much easier to just drop in.
Where is "size/speed" tradeof.
If you do have some math-intensive code, for example, where is a
"threshhold" - then this chunk of code grown large enough to not
fit to stack, performance drops drammaticaly. So _generaly_, its
prefered to minimize code size.
If, from the other side, you had rearranged your algorithm to make
a streamlined instructions flow, then it could be more productive
to "unroll" code, to exclude branches e.t.c.
I understand that. Again, my question just had to do with why -O3 was
making smaller, faster code than -Os which Eric Albert answered (by
the way, thank you for that, Eric).
- Steve
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