On 01/22/2011 11:28 PM, Sergio Belkin wrote:
> 2011/1/22 Jason L Tibbitts III<firstname.lastname@example.org>:
>>>>>>> "SB" == Sergio Belkin<email@example.com> writes:
>> SB> Is it allowed to override "-O2" and use instead "-O3"? I see that
>> SB> those flags overrides those CXXFLAGS from Makefile sources.
>> Of course for your personal packages you can do whatever you like. In
>> Fedora, though, the answer is that you should use the provided optflags
>> unless you have specific justification for a change. In order to change
>> -O2 to -O3 I'd want to see benchmarking and other such evidence that
>> indicates that the change actually makes a difference. Otherwise it's
>> just a case of "adding -O99 for uber mega speedz0rs!!!11!!1one".
>> - J<
>> packaging mailing list
> Thanks for the answer, could you tell me (I'm really no ironic) could
> you tell me when I can find that such a evidence.
Well, I am not sure if I understand correctly.
The problem with -O3 vs. -O2 is -O3 turning on, less-tested agressive
* may trip over bugs inside of the compiler (e.g. compiler ICEs).
* may cause mis-compiled/defective binaries.
* may break interaction with other tools (e.g. break debuginfos)
Also, "-O2 vs. -O3" benchmarks are of little significance, because
individual upstreams have little possibility to know about the
generality and significance of such benchmarks. I.e. though an upstream
may be able to prove "-O3 is 5% faster for application XXX on
Ubuntu-Y-x86_64", this figure doesn't tell much about the impact of "-O3
> Let's say that I forget the "-O3" issue. Can I use that CXXFLAGS
> "-ansi -Wall -Wno-deprecated" ?
-ansi normally doesn't affect code generation, so it's mostly harmless.
-ansi however is somewhat problematic when it comes to portability,
because the impact of -ansi is not consistent across different OSes.
Adding further warning flags (-W*; not -Wno-* == suppressing warnings)
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