[LLVMdev] Detect if a basicblock is part of a loop

Cristianno Martins
Thu, 26 Apr 2012 15:52:32 -0000

Hi Rinaldini,

In order to find information about loops inside a given function you should use
something like "LoopInfo *LI = P->getAnalysis<LoopInfo>()",
remembering to add "AU.addRequired<LoopInfo>();" to your
getAnalysisUsage method.

If the function you are interested to is not located in the module being
compiled (if you created it as an auxiliary function, for example), you could
create this information by simply creating a DominatorTreeBase of your function
and using it to calculate the LoopInfo, as below:
    DominatorTreeBase<BasicBlock> *DTB;
    DTB = new DominatorTreeBase<BasicBlock>(false);
    DTB->recalculate(*AuxFunction);

    LoopInfoBase<BasicBlock, Loop> LIB;
    LIB.Calculate(*DTB);

Cheers,

--
Cristianno Martins
PhD Student of Computer Science
University of Campinas
cmartins at ic.unicamp.br


On Thursday, 26 de April de 2012 at 11:57, Hal Finkel wrote:

> Rinaldini,
>
> What exactly did you run? Specifically, you may be missing some
> analysis passes that are necessary for LoopInfo to have the loop
> information you desire.
>
> -Hal
>
> On Thu, 26 Apr 2012 14:02:04 +0000
> Rinaldini Julien <julien.rinaldini at heig-vd.ch
(mailto:julien.rinaldini at heig-vd.ch)> wrote:
>
> > Hi,
> >
> > I'm trying to detect if a basicblock is part of a loop or not.
> >
> > I tried the llvm::LoopInfo like that
> >
(http://llvm.org/docs/doxygen/html/classllvm_1_1LoopInfo.html#a4abca289c73cd09487e05d11d9f7d877):
> >
> > LoopInfo *loop = new LoopInfo();
> > bool isLoop = loop->getLoopFor(myBB); // getLoopFor - Return the
> > inner most loop that BB lives in. If a basic block is in no loop (for
> > example the entry node), null is returned. See doxygen
> >
> > But getLoopFor() always return me NULL even if my basicblock is
> > inside a for loop... I tried this:
> > http://comments.gmane.org/gmane.comp.compilers.llvm.devel/38490 but
> > it didn't work too :(
> >
> > Any advice?
> > Thx
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >
>
>
>
>
> --
> Hal Finkel
> Postdoctoral Appointee
> Leadership Computing Facility
> Argonne National Laboratory
> _______________________________________________
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> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>


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