Re: xcode 1.2, -fast and ppc_intrinsics.h
Re: xcode 1.2, -fast and ppc_intrinsics.h
- Subject: Re: xcode 1.2, -fast and ppc_intrinsics.h
- From: Glen Low <email@hidden>
- Date: Fri, 30 Apr 2004 23:54:39 +0800
Mark:
On 29/04/2004, at 10:12 PM, Mark Eissler wrote:
On Apr 28, 2004, at 8:26 PM, Glen Low wrote:
The C89/C99 and C++98 aliasing rules state that you shall not access
an object of type X through an lvalue (e.g. pointer, reference) of
type Y, where X and Y are unrelated. Perhaps this is interacting
badly with ObjC. (In C++, X and Y can be related through inheritance,
but in C there's no such thing so I don't know how it falls out in
ObjC).
Yes. I think the problem is ObjC as I'm not recasting.
Could we have a look at a snippet of bad code?
In practice the aliasing rules really only optimize tight, inlined
loops, so you should be quite safe leaving it off ObjC code. You
might try -fno-strict-aliasing in addition to -fast to do this
(caveat -- haven't tried this myself).
I haven't tried it either but I don't think you can do that. Since
-fast turns on the strict aliasing flag, it will probably override
-fno-strict-aliasing. At least, this is what it will do with the
optimization flag (-fast turns on -O3, if you specify anything else it
will be overridden).
I'm pretty sure that -fno-xxx turns off xxx explicitly in the face of
other optimizations, otherwise there would be no use for -fno-xxx.
Cheers, Glen Low
---
pixelglow software | simply brilliant stuff
www.pixelglow.com
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