Re: -O4 a.k.a. link-time optimization
Re: -O4 a.k.a. link-time optimization
- Subject: Re: -O4 a.k.a. link-time optimization
- From: Glen Low <email@hidden>
- Date: Tue, 07 Jun 2011 12:24:21 +0800
Sean
On 07/06/2011, at 12:49 AM, Sean McBride wrote:
On Sat, 4 Jun 2011 19:43:34 +0800, Glen Low said:
I'd like any tips/experience/caveats with using link-time
optimization.
I've tried building several of the 3rd party open source projects I
use
with -O4, and all of them fail. They do build at -00 and -O3 however.
My impression is that -O4 is not fully baked. It's been a few months
since I've tried however, maybe things are better now.
I had a similar experience with open-source Graphviz, pre-4.0. The
current Xcode seems to build it cleanly though -- the resulting object
files at -O4 appear to be LLVM bytecode and not native code, and the
linker seems to handle everything nicely. I ended up with around a 4%
speed up on x64 code, the small delta probably more a testament to the
efficiency of Graphviz code rather than the inefficiency of LTO. Just
want to be sure whether I should flip the switch on my iOS/armv7 code
or not.
Cheers, Glen Low
---
pixelglow software | simply brilliant stuff
www.pixelglow.com
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