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Re: Stupid Intel question
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Re: Stupid Intel question


  • Subject: Re: Stupid Intel question
  • From: Urs Heckmann <email@hidden>
  • Date: Fri, 17 Mar 2006 23:27:23 +0100

Hi Steve,

schrieb Steve Checkoway:

As was just discussed on the Xcode-users list, -ftree-vectorize enables -fstrict-aliasing which is breaking code in the CoreAudio SDK. To quote Eric Albert:

We turn off strict aliasing by default because, as you've noticed, it breaks a lot of code (even though it's more correct and results in faster code). But we explicitly turn it on for -O2 and higher when -ftree-vectorize is passed to the compiler, as you're doing here. I'm not sure why, but it doesn't seem right to me, particularly when -fno-strict-aliasing is passed.

Thanks for the info! I was almost going nuts about it.

It's interesting to note that you're having problems on Intel but not PowerPC as it was the other way around in the thread "GCC 4 and strict aliasing" in the Xcode list.

I know this wasn't much help, but it seems that for now you should probably not use -ftree-vectorize nor -fstrict-aliasing, at least until the code and/or the compiler gets fixed.

I've used it on Panther/gcc3 without problems. Havn't tried the UBs on the PowerPC yet, so I don't know if it's corrosive there too.


My code is noticably faster with strict-aliasing, so I hope it'll be fixed soon!

Cheers,

;)  Urs
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References: 
 >Stupid Intel question (From: Urs Heckmann <email@hidden>)
 >Re: Stupid Intel question (From: Steve Checkoway <email@hidden>)

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