Re: dereferencing type-punned pointer will break strict-aliasing rules
Re: dereferencing type-punned pointer will break strict-aliasing rules
- Subject: Re: dereferencing type-punned pointer will break strict-aliasing rules
- From: Michael Monscheuer <email@hidden>
- Date: Fri, 19 May 2006 09:26:23 +0200
Hi!
Switching ON Auto-vectorization seems to switch on strict aliasing implicitly.
Documentation of compiler settings and GUI ('Enforce Strict Aliasing' option)
do not reflect this in XCode (All tested with -O3 and -Os. With optimization level -O0
Auto-vectorization option is ignored).
You do not have aliasing warnings with development configurations, as Xcode switches off
optimization in that case (-O0) to enable debugging, I think.
Right?
Michael
Eric Albert schrieb:
On May 17, 2006, at 7:40 AM, Ulf Dunkel wrote:
I create UB "deployment" builds of a project and get masses of
warnings "dereferencing type-punned pointer will break strict-aliasing
rules" then.
When I build "development native" on a PowerPC Mac, no such warning is
shown.
Googling around I found that GCC sets a flag -fstrict-aliasing when
-O2 is set. This seems to lead to these warnings when building for
Intel Macs.
How do I tell GCC in XCode that it should use -fno-strict-aliasing?
Actually, -fstrict-aliasing is turned off by default in Apple's gcc.
The documentation is wrong. But it sounds like it's being turned on in
your case. Show us the detailed build log of the compiler invocation
for one of the source files which produces these warnings and we should
be able to figure out what's going on.
-Eric
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