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: Sean McBride <email@hidden>
- Date: Wed, 08 Jun 2011 16:22:18 -0400
- Organization: Rogue Research Inc.
On Tue, 7 Jun 2011 12:24:21 +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.
I don't touch Xcode 4 with a 10 foot pole, but I have been using a build
of clang from svn from a few days ago. I just tried again with a couple
of open source projects. With one, I get crazy link errors at -O4, with
the other it now links, where it did not months ago.
So it seems it has progressed, but is not quite fully baked yet.
Looking forward to it though!
Cheers,
--
____________________________________________________________
Sean McBride, B. Eng email@hidden
Rogue Research www.rogue-research.com
Mac Software Developer Montréal, Québec, Canada
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