[PATCH] D63155: [clang][NewPM] Fix broken profile test

[Rong Xu via Phabricator via cfe-commits]

xur added a comment.

they are not doing the exacly the same thing for old pass manager and new pass manger: old pass manger is doing instrumentation, while the new pass manager with this change is NOT.
the test is not check instrumentation, (it only check the variables that generates by InstroProfiling pass). 
In this sense, the test is not well written.

I can draft a patch for this.

In D63155#1563239 <https://reviews.llvm.org/D63155#1563239>, @chandlerc wrote:

> In D63155#1563229 <https://reviews.llvm.org/D63155#1563229>, @xur wrote:
>
> > This patch does not make sense to me.
> >
> > The reason of failing with -fexperimental-new-pass-manager is because we don't do PGO instrumentation at -O0. This is due to the fact that PGO instrumentation/use passes are under PassBuilder::buildPerModuleDefaultPipeline.
> >
> > This patch add a pass
> >
> >   MPM.addPass(PGOInstrumentationGenCreateVar(PGOOpt->ProfileFile));
> >
> > which only gives you the wrong signal  of instrumentation is done.
> >
> > I wrote pass PGOInstrumentationGenCreateVar only for some trick interactions for thinlto under ldd for CSPGO.
> >  Regular FDO should not use it.
> >
> > The right fix is to enable PGO instrumentation and use in pass builder for O0.
> >
> > I would like to request to revert this patch.
>
>
> I mean, I'm happy for the patch to be reverted, but I still really don't understand why this fixes the test to work *exactly* the same as w/ the old pass manager and doesn't break any other tests if it is completely wrong? It seems like there must be something strange with the test coverage if this is so far off of correct without any failures...
>
> I also don't understand what fix you are suggesting instead, but maybe you can show a patch?




In D63155#1563266 <https://reviews.llvm.org/D63155#1563266>, @chandlerc wrote:

> In D63155#1563240 <https://reviews.llvm.org/D63155#1563240>, @leonardchan wrote:
>
> > In D63155#1563229 <https://reviews.llvm.org/D63155#1563229>, @xur wrote:
> >
> > > This patch does not make sense to me.
> > >
> > > The reason of failing with -fexperimental-new-pass-manager is because we don't do PGO instrumentation at -O0. This is due to the fact that PGO instrumentation/use passes are under PassBuilder::buildPerModuleDefaultPipeline.
> > >
> > > This patch add a pass
> > >
> > >   MPM.addPass(PGOInstrumentationGenCreateVar(PGOOpt->ProfileFile));
> > >
> > > which only gives you the wrong signal  of instrumentation is done.
> > >
> > > I wrote pass PGOInstrumentationGenCreateVar only for some trick interactions for thinlto under ldd for CSPGO.
> > >  Regular FDO should not use it.
> > >
> > > The right fix is to enable PGO instrumentation and use in pass builder for O0.
> > >
> > > I would like to request to revert this patch.
> >
> >
> > As an alternative, could I instead request that we remove the BackendUtil changes and just mark the runs in gcc-flag-compatibility.c with `-fno-experimental-new-pass-manager`. This way we could clarify that under the new PM, we shouldn't run PGO at -O0? If not, I'll revert this patch as is.
>
>
> No, I think we should be doing PGO at O0 in the new PM if we do so in the old PM.
>
> I think Rong is saying that the *way* you're enabling PGO at O0 isn't correct to fix this test case. That seems plausible to me at least, and I think reverting and figuring out what the right way to do it is a fine approach.
>
> I just think we also need to understand why *no other test failed*, and why the only test we have for doing PGO at O0 is this one and it could be "fixed" but such a deeply unrelated change....





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