llvm dev - Apr 2012 - [LLVMdev] Detect if a basicblock is part of a loop

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
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> 
> 

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Hi,

Depending on what have run before your pass, the loop may have been unrolled or
simplified if the computation inside the loop is too simple.

Cheers,
--
Arnaud de Grandmaison

________________________________________
From: llvmdev-bounces at cs.uiuc.edu [llvmdev-bounces at cs.uiuc.edu] On Behalf
Of Cristianno Martins [cristiannomartins at gmail.com]
Sent: Thursday, April 26, 2012 5:52 PM
To: Hal Finkel
Cc: llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] Detect if a basicblock is part of a loop

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
_______________________________________________
LLVM Developers mailing list
LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

Thx all for the quick answers...
> De : llvmdev-bounces at cs.uiuc.edu [llvmdev-bounces at cs.uiuc.edu] de la
part de Arnaud ALLARD DE GRANDMAISON [arnaud.allarddegrandmaison at parrot.com]
>
> Hi,
>
> Depending on what have run before your pass, the loop may have been
unrolled or simplified if the computation inside the loop is too simple.
>
> Cheers,
> --
> Arnaud de Grandmaison
Just as I said to Hal, nothing else than:
$ clang -emit-llvm -S -o main.ll main.c
$ ../build/Release/bin/opt -load ../build/Release/lib/LLVMobfuscationTest.so
-flattening -S main.ll -o main.opt.ll
> From: llvmdev-bounces at cs.uiuc.edu [llvmdev-bounces at cs.uiuc.edu] On
Behalf Of Cristianno Martins [cristiannomartins at gmail.com]
> 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
Thx, I'll try that... I guess I missed the Dominator step last time
> 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
I'm running opt with my lib on a ir code emmitted by clang: $ clang
-emit-llvm -S -o main.ll main.c
and opt: $ ../build/Release/bin/opt -load
../build/Release/lib/LLVMobfuscationTest.so -flattening -S main.ll -o
main.opt.ll

No others optimization applied...