[llvm-dev] LLVM - getAnalysisUsage()

[Daniel Berlin via llvm-dev]

This is expected if those analysis are not preserved.


On Fri, Jan 22, 2016 at 12:49 PM, Syed Rafiul Hussain via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I have added -debug-pass=Structure, and found the following:
>
> ModulePass Manager
>     X Analysis
>       Unnamed pass: implement Pass::getPassName()
>     FunctionPass Manager
>       Module Verifier
>     Bitcode Writer
> Pass Arguments:  -x -y -z
>   FunctionPass Manager
>     X Analysis
>     Y Construction
>     Z Construction
>
> Even for getAnalysis<Y>(*F) and getAnalysis<Z>(&F), all the passes X,
> Y, Z are executed again. In total there are three places where
> getAnalysis() directive has been used for X, Y, Z. However, for each
> getAnalysis() call, all three passes are scheduled/executed.
>
>
>
>
> On Fri, Jan 22, 2016 at 12:24 PM, Mehdi Amini <mehdi.amini at apple.com>
> wrote:
> >
> >> On Jan 21, 2016, at 9:05 PM, Syed Rafiul Hussain via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >>
> >> Hi,
> >>
> >> I am using llvm-3.8 for my project. Following is my getAnalysisUsage()
> method:
> >>
> >> virtual void getAnalysisUsage(AnalysisUsage &AU) const override
> >> {
> >>   AU.setPreservesAll();
> >>   AU.addRequired<X>();
> >>   AU.addRequired<Y>();
> >>   AU.addRequired<Z>();
> >> }
> >>
> >> Now, if I call getAnalysis<X>(*F), instead of invoking just the X
> >> pass, all the passes, i.e., X, Y and Z are being invoked. Could anyone
> >> help me in this regard?
> >
> > This is expected. With the current pass manager, the scheduling is done
> upfront. The “addRequired” directive tells the pass manager that before
> even starting to run your pass, it needs to schedule X, Y, and Z.
> > They will run even without the call to  getAnalysis<X>(*F). The new pass
> manager (not complete yet but almost) will change that.
> >
> > When running your pass with opt, you can add —debug-pass=Structure to
> see what the scheduling is.
> >
> > I hope I didn’t misunderstand your question.
> >
> > —
> > Mehdi
> >
>
>
>
> --
> Rafi
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>
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