[PATCH] D22141: [BFI] Add option to lazily calculate BFI

[Xinliang David Li via llvm-commits]

The idea of lazyBFI analysis sounds good to me. Need to see what the actual
patch look like :)

David

On Mon, Jul 11, 2016 at 2:18 PM, Adam Nemet <anemet at apple.com> wrote:

> anemet added a comment.
>
> > In http://reviews.llvm.org/D22141#478534, @davidxl wrote:
>
> >
>
> > > I suggest just making BFI lazy itself (when getBlockFreq() is first
> called ...). In fact  I think the laziness handling should be in
> BlocFrequencyInfoImpl class. By so doing, MBFI can get the laziness
> automatically as well.
>
> >
>
>
> I've tried and unfortunately, I don't think this will work.  I saw two
> issues:
>
> a. LoopInfo is freed by the time block frequencies are requested
>
>   This can be fixed by making users of BFI also dependent on LI but that's
> an overkill for existing users
>
> b. The pass starts modifying the CFG and when it tries to update the
> frequencies LI and the CFG are already inconsistent
>
> I think that these issues (there maybe more) are difficult to fix in the
> context of existing BFI's users.  My new proposal is to introduce a new
> analysis, LazyBFI.  Then, new users could opt in by complying with LBFI's
> requirements:
>
> 1. require LI and BPI as well (I will add an 'required' enumerator)
>
> 2. compute BFI before making any CFG changes
>
> The analysis would effectively consist of the LazyBFI class I had
> earlier.  It will only cover IR BFI for now but we could later template-ize
> it to also work with BFI.
>
> I talked with Duncan about this and he was fine with this idea.  Let me
> know your thoughts.
>
> Adam
>
>
> http://reviews.llvm.org/D22141
>
>
>
>
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