On Fri, Nov 19, 2021 at 9:55 AM Martin Jambor <mjam...@suse.cz> wrote: > > Hi, > > On Fri, Nov 19 2021, Jan Hubicka wrote: > >> > Hi, > >> > > >> > On Fri, Nov 12 2021, Martin Jambor wrote: > >> > > 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.) > >> > > > >> > > >> > Unfortunately, I was wrong, there are testcases which use the optimize > >> > attribute to switch a function to Ofast and those ICE because > >> > -fsemantic-interposition is not an optimization flag and only > >> > optimization flags can change in an optimize attribute (AFAIK, I only > >> > had a quick glance at the results). > >> > > >> > I am not sure what is the right way to tackle this, whether to set the > >> > flag at Ofast in some nonstandard way or make the flag an optimization > >> > flag - probably affecting function definitions, having it affect > >> > call-sites seems too fine-grained. I will try to discuss this on IRC on > >> > Monday (and hope such change is still doable early stage3). > >> > > >> > Sorry for posting this a bit prematurely, > >> > >> Hi, > >> > >> This patch turns flag_semantic_interposition to optimization option so > >> it can be enabled with per-function granuality. This is done by adding > >> the flag among visibility flags into the symbol table. This fixes the > >> behaviour on the testcase I added to testsuite. > >> > >> There are bugs where get_availability misbehaves on partitioned program. > >> We can also use the new flag to fix those, but I will do that > >> incrementally. > >> > >> The -Ofast change should be safe now. > > > > Also forgot to say it explicitly, the patch is OK, so please commit it. > > > > Thanks a lot for the enabling patch. I have committed mine after re-testing. > > Martin
Perhaps reconsider https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100937 (configure: Add --enable-default-semantic-interposition)? Patch: https://gcc.gnu.org/pipermail/gcc-patches/2021-June/572018.html I happen a write-up on https://maskray.me/blog/2021-05-09-fno-semantic-interposition -- 宋方睿
