llvm dev - Dec 2012 - [LLVMdev] LoopPass doFinalization() called multiple times per program?

I'm wondering if the documentation for LoopPass (
http://llvm.org/docs/WritingAnLLVMPass.html#LoopPass) is misleading or
incorrect (or if I'm just missing something.) The documentation states:

"The doFinalization method ... is called when the pass framework has
finished calling
runOnLoop<http://llvm.org/docs/WritingAnLLVMPass.html#runOnLoop> for
every loop in the program being compiled."
>From this, I understood that for a single instance of a LoopPass sub-class,
the doFinalization method would be called exactly once, after all loops had
been seen. However in practice I am seeing doFinalization() being called
multiple times per program. Digging into the code, it appears that
LPPassManager actually makes the calls to doFinalization() at the end of
it's runOnFunction() method (
http://llvm.org/docs/doxygen/html/LoopPass_8cpp_source.html#l00281, at time
of writing). This therefore means that doFinalization() can be called
multiple times per LoopPass; as many as there are functions defined in the
input file.

Assuming I have made no mistakes here, is this a case of poorly written
documentation, or an error in the implementation? I note that FPPassManager
does it calls to FunctionPass' doFinalization() in it's own
doFinalization() method, which seems the correct behaviour to me.

Thanks,
Stephen
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Hi Stephen,

On 13/12/12 18:58, Stephen McGruer wrote:
> I'm wondering if the documentation for LoopPass
> (http://llvm.org/docs/WritingAnLLVMPass.html#LoopPass) is misleading or
> incorrect (or if I'm just missing something.) The documentation states:
>
> "The doFinalization method ... is called when the pass framework has
finished
> calling runOnLoop
<http://llvm.org/docs/WritingAnLLVMPass.html#runOnLoop> for
> every loop in the program being compiled."
>
>  From this, I understood that for a single instance of a LoopPass
sub-class, the
> doFinalization method would be called exactly once, after all loops had
been
> seen. However in practice I am seeing doFinalization() being called
multiple
> times per program. Digging into the code, it appears that LPPassManager
actually
> makes the calls to doFinalization() at the end of it's runOnFunction()
method
> (http://llvm.org/docs/doxygen/html/LoopPass_8cpp_source.html#l00281, at
time of
> writing). This therefore means that doFinalization() can be called multiple
> times per LoopPass; as many as there are functions defined in the input
file.
my understanding is that this is the expected behaviour and the documentation
should be improved (want to propose a patch?).

Ciao, Duncan.
>
> Assuming I have made no mistakes here, is this a case of poorly written
> documentation, or an error in the implementation? I note that FPPassManager
does
> it calls to FunctionPass' doFinalization() in it's own
doFinalization() method,
> which seems the correct behaviour to me.
>
> Thanks,
> Stephen
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

On Sun, Dec 16, 2012 at 7:23 AM, Duncan Sands <baldrick at free.fr> wrote:
> Hi Stephen,
>
>
> On 13/12/12 18:58, Stephen McGruer wrote:
>
>> I'm wondering if the documentation for LoopPass
>>
(http://llvm.org/docs/**WritingAnLLVMPass.html#**LoopPass<http://llvm.org/docs/WritingAnLLVMPass.html#LoopPass>)
>> is misleading or
>> incorrect (or if I'm just missing something.) The documentation
states:
>>
>> "The doFinalization method ... is called when the pass framework
has
>> finished
>> calling runOnLoop <http://llvm.org/docs/**WritingAnLLVMPass.html#**
>> runOnLoop
<http://llvm.org/docs/WritingAnLLVMPass.html#runOnLoop>> for
>>
>> every loop in the program being compiled."
>>
>>  From this, I understood that for a single instance of a LoopPass
>> sub-class, the
>> doFinalization method would be called exactly once, after all loops had
>> been
>> seen. However in practice I am seeing doFinalization() being called
>> multiple
>> times per program. Digging into the code, it appears that LPPassManager
>> actually
>> makes the calls to doFinalization() at the end of it's
runOnFunction()
>> method
>>
(http://llvm.org/docs/doxygen/**html/LoopPass_8cpp_source.**html#l00281<http://llvm.org/docs/doxygen/html/LoopPass_8cpp_source.html#l00281>,
>> at time of
>> writing). This therefore means that doFinalization() can be called
>> multiple
>> times per LoopPass; as many as there are functions defined in the input
>> file.
>>
>
> my understanding is that this is the expected behaviour and the
> documentation
> should be improved (want to propose a patch?).
>
I'm actually really hoping to change this behavior in the not-too-distant
future.

The goal that I and several others have worked out is that for *all*
passes, the doInitialization and doFinalization are called once per module.
All of the doInitialization methods should be called before the first
pass's runOn***  method is called, and all of the doFinalization calls
should be after the last pass's runOn*** have finished.

The goal of the initialization and finalization methods is to allow
per-module caching, uniquing, setup, and teardown.

I know that we are quite far from this goal in practice sadly, but I think
the goal remains the same.

>
> Ciao, Duncan.
>
>
>> Assuming I have made no mistakes here, is this a case of poorly written
>> documentation, or an error in the implementation? I note that
>> FPPassManager does
>> it calls to FunctionPass' doFinalization() in it's own
doFinalization()
>> method,
>> which seems the correct behaviour to me.
>>
>> Thanks,
>> Stephen
>>
>>
>> ______________________________**_________________
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>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>
http://lists.cs.uiuc.edu/**mailman/listinfo/llvmdev<http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>
>>
>>
> ______________________________**_________________
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>
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