llvm dev - Aug 2019 - Doubt regarding getAnalysisUsage

Hi,

I have a doubt regarding *getAnalysisUsage.* My assumption is that, as
analysis passes will not change the IR, all the passes required by an
analysis pass should be preserved. Say, I have an analysis pass which
requires another analysis pass called *SomeAnalysis* and I have not
added *AU.addPreserved<SomeAnalysis>()
*to my pass.

Would the pass manager still considers the *SomeAnlaysis *as preserved?
-- 
Regards,
DTharun
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Hi,

the legacy pass manager (the one that uses getAnalysisUsage) makes no
distinction between analyses and other passes. E.g., passes can also
depend on transformative passes. If your pass is does not change the
IR, then you can add AU.setPreservesAll() into getAnalysisUsage. Any
additional addPreserved calls will have no effect as you told the pass
manager already that you preserve all passes.If you do not add
setPreservesAll/addPreserved the pass manager will treat your pass as
a transformative pass and re-compute SomeAnalysis after your pass has
run.

Michael


Am Di., 13. Aug. 2019 um 23:33 Uhr schrieb Dangeti Tharun kumar via
llvm-dev <llvm-dev at lists.llvm.org>:
>
> Hi,
>
> I have a doubt regarding getAnalysisUsage. My assumption is that, as
analysis passes will not change the IR, all the passes required by an analysis
pass should be preserved. Say, I have an analysis pass which requires another
analysis pass called SomeAnalysis and I have not added
AU.addPreserved<SomeAnalysis>() to my pass.
>
> Would the pass manager still considers the SomeAnlaysis as preserved?
> --
> Regards,
> DTharun
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

On Wed, Aug 14, 2019 at 10:21 PM Michael Kruse <llvmdev at meinersbur.de>
wrote:
> Hi,
>
> the legacy pass manager (the one that uses getAnalysisUsage) makes no
> distinction between analyses and other passes. E.g., passes can also
> depend on transformative passes. If your pass is does not change the
> IR, then you can add AU.setPreservesAll() into getAnalysisUsage. Any
> additional addPreserved calls will have no effect as you told the pass
> manager already that you preserve all passes.

> >If you do not add
> setPreservesAll/addPreserved the pass manager will treat your pass as
> a transformative pass and re-compute SomeAnalysis after your pass has
> run.
>
I am under the impression that the pass manager will re-run the
un-preserved analysis passes only if the current pass returns with a
'true'.
>
> Michael
>
>
> Am Di., 13. Aug. 2019 um 23:33 Uhr schrieb Dangeti Tharun kumar via
> llvm-dev <llvm-dev at lists.llvm.org>:
> >
> > Hi,
> >
> > I have a doubt regarding getAnalysisUsage. My assumption is that, as
> analysis passes will not change the IR, all the passes required by an
> analysis pass should be preserved. Say, I have an analysis pass which
> requires another analysis pass called SomeAnalysis and I have not added
> AU.addPreserved<SomeAnalysis>() to my pass.
> >
> > Would the pass manager still considers the SomeAnlaysis as preserved?
> > --
> > Regards,
> > DTharun
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>

-- 
Regards,
DTharun
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