Re: -O3 vs. -Os
Re: -O3 vs. -Os
- Subject: Re: -O3 vs. -Os
- From: Steve Checkoway <email@hidden>
- Date: Tue, 17 Jan 2006 01:06:24 -0800
On Jan 16, 2006, at 11:50 PM, Rustam Muginov wrote:
Perharbs this is more suitable for "performance-optimization"
dev.list., but:
It's related to the recommendation that I've seen a number of times
on this list regarding the use of -Os
Regular applications do not have heavy computation mathematics and
do not have clearly visible "hot-spots", i.e. small parts of code
where application spend something like 50% or more total time.
I would recommend you to use Shark (part of the CHUD tools) to
investigate application run-time behaviour
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.
Still, I wonder on what you were basing your assertion that only
"manually-tuned high-performance libraries" benefit from -O3. I
wouldn't claim that this game is manually tuned at all. Plus, I would
think that such code would benefit the least from optimization if it
is carefully done by hand to begin with.
I think in this case it is pretty clear that more highly optimized
code that is actually smaller than the less optimized code is likely
to run faster. Based on framerates (turning vsync off, of course),
that is the case.
I'm curious if this is normal.
- Steve
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