Re: "-fno-unswitch-loops" option have no effect?

[Alexander Strange <astrange@ithinksw.com>]

On Aug 17, 2009, at 10:50 AM, Bernd Roesch wrote:

>> [..]
>> There is no need for much detail, just compile any bigger  
>> sourcecode with
>> -O3 -fno-.. and after that with -O2 .... When the object files are  
>> not
>> identical, something is wrong and I can start a bug report.
>
> how much is size diffrent ?
>
> You use
> -finline-functions -fpredictive-commoning -fgcse-after-reload
> -ftree-vectorize
>
> right ?
>
> I see in Gcc source that there is more set on -O3.
> flag_ipa_cp_clone = opt3;
> if (flag_ipa_cp_clone)
>   flag_ipa_cp = 1;
>
> .but i
> think you can easy test, compile the ffmpeg, if it give no internal
> compiler error with -fno........ then it work.
>
> here is from source opt.c what is set on opt3
>
> opt3 = (optimize >= 3);
> flag_predictive_commoning = opt3;
> flag_inline_functions = opt3;
> flag_unswitch_loops = opt3;
> flag_gcse_after_reload = opt3;
> flag_tree_vectorize = opt3;
> flag_ipa_cp_clone = opt3;
> if (flag_ipa_cp_clone)
>   flag_ipa_cp = 1;

That doesn't cover all of it; for instance, complete loop unrolling  
increases code size more on -O3.

That means you run into http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40992 
  with ffmpeg's asm enabled, but turning it down (--param max- 
completely-peel-times=2) actually seems slightly faster even with  
plain C on i386.