[LLVMdev] LoopPass doFinalization() called multiple times per program?

[Duncan Sands]

Hi Chandler,

On 17/12/12 13:47, Chandler Carruth wrote:
> On Sun, Dec 16, 2012 at 7:23 AM, Duncan Sands <baldrick at free.fr
> <mailto: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.

would it still be possible to optimize and codegen functions as they are output
(rather than waiting for the module to be completely output before doing this)?

Ciao, Duncan.

>
> 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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