[PATCH] options: Make -Ofast switch off -fsemantic-interposition

Jan Hubicka hubicka@kam.mff.cuni.cz
Fri Nov 12 15:40:49 GMT 2021


> Hi,
> 
> using -fno-semantic-interposition has been reported by various people
> to bring about considerable speed up at the cost of strict compliance
> to the ELF symbol interposition rules  See for example
> https://fedoraproject.org/wiki/Changes/PythonNoSemanticInterpositionSpeedup
> 
> As such I believe it should be implied by our -Ofast optimization
> level, not only so that benchmarks that can benefit run faster, but
> also so that people looking at -Ofast documentation for options that
> could speed their programs find it.
> 
> I have verified that with the following patch IPA-CP sees
> flag_semantic_interposition set to zero at Ofast and that info and pdf
> manual builds fine with the documentation change.  I am bootstrapping
> and testing it now in order to comply with submission criteria but I
> don't think an Ofast change gets much tested.
> 
> Assuming it passes, is the patch OK?  (If it is, I will also add a note
> about it in the "Caveats" section in gcc-12/changes.html of wwwdocs
> after I commit the patch.)
> 
> Thanks,
> 
> Martin
> 
> 
> gcc/ChangeLog:
> 
> 2021-11-12  Martin Jambor  <mjambor@suse.cz>
> 
> 	* opts.c (default_options_table): Switch off
> 	flag_semantic_interposition at Ofast.
> 	* doc/invoke.texi (Optimize Options): Document that Ofast switches off
> 	-fsemantic-interposition.
OK,
thanks!
Honza


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