On 2012-09-05 11:36, David Chisnall wrote:
On 5 Sep 2012, at 10:31, Dimitry Andric wrote:
TThe
-fno-strict-aliasing is not really my choice, but it was introduced
in the past by Nathan Whitehorn, who apparently saw problems without
it. It will hopefully disappear in the future.
Clang currently defaults to no strict aliasing on FreeBSD.
Yes, but upstream has never used -fno-strict-aliasing, just plain -O2.
I run regular separate builds of pristine upstream clang on FreeBSD, and
I haven't seen any failures due aliasing problems in all the regression
tests. That doesn't guarantee there are no problems, of course...
In my experience, most C programmers misunderstand the aliasing rules of C and
even people on the C++ standards committee often get them wrong for C++, so
trading a 1-10% performance increase for a significant chance of generating
non-working code seems like a poor gain. If people are certain that they do
understand the rules, then they can add -fstrict-aliasing to their own CFLAGS.
I'm actually quite interested in the performance difference; I think I
will run a few tests. :)
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