llvm dev - May 2020 - Creating a copy Pass of DependenceAnalysis

Hi,

I want to create a copy of DependenceAnalysis downstream.

At first I tried the HelloWorld tutorial. But then I figured, maybe I
should move on
to create my pass by mimicking some other pass in LLVM.

So, I tried copying DependenceAnalysis itself [1]

Although after a lot of time of trying it compiled, I'm pretty sure I have
done it
completely in the wrong way. What is more, I can't access my pass with the
argument
I put (-rt-dep-checks).

Then, I watched this tutorial [2]. Apart from the fact that there seem to be
way too many steps just to create hello world pass, I don't think that
passes like
DependenceAnalysis follow it.

So, what should I do? What is the "correct" to create the copy; like
an
external
library as the HelloWorld tutorial shows ?

Thanks,
Stefanos

[1] https://github.com/baziotis/llvm-project/tree/dep_analysis
[2] https://www.youtube.com/watch?v=ar7cJl2aBuU
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> On May 22, 2020, at 15:42, Stefanos Baziotis via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hi,
> 
> I want to create a copy of DependenceAnalysis downstream.
> 
> At first I tried the HelloWorld tutorial. But then I figured, maybe I
should move on
> to create my pass by mimicking some other pass in LLVM.
> 
> So, I tried copying DependenceAnalysis itself [1]
> 
> Although after a lot of time of trying it compiled, I'm pretty sure I
have done it
> completely in the wrong way. What is more, I can't access my pass with
the argument
> I put (-rt-dep-checks).
> 
For the new pass manager I think you have to add your pass to
llvm/lib/Passes/PassRegistry.def.

I’d recommend taking a look at how the DominatorTree analysis is set up. Also
note that analysis passes on their own are invoked a little bit differently to
transformation passes: old PM:  `opt -domtree -analyze foo.ll`, new PM: `opt 
-passes='print<domtree>’ foo.ll`
> Then, I watched this tutorial [2]. Apart from the fact that there seem to
be
> way too many steps just to create hello world pass, I don't think that
passes like
> DependenceAnalysis follow it.
IIRC the tutorial is mostly focusing on out-of-tree passes, so the steps are
different to an in-tree pass. It looks like the in-tree docs also mostly cover
out-of-tree passes (http://llvm.org/docs/WritingAnLLVMPass.html). Improvements
to the docs in that area would definitely be welcomed.

> [1] https://github.com/baziotis/llvm-project/tree/dep_analysis
I had a quick look and it looks like your new pass is called
RuntimeDependenceChecks.

Just in case you are not aware, there is already infrastructure to create
runtime checks for dependences in loops in tree:
https://github.com/llvm/llvm-project/blob/master/llvm/lib/Analysis/LoopAccessAnalysis.cpp

Cheers,
Florian

> For the new pass manager I think you have to add your pass to
llvm/lib/Passes/PassRegistry.def.

Oh ok, I'll try it.
> I’d recommend taking a look at how the DominatorTree analysis is set up.
Also note that analysis passes on their own are invoked a little bit
differently to transformation passes: old PM:  `opt -domtree -analyze
foo.ll`, new PM: `opt  -passes='print<domtree>’ foo.ll`

I'll take a look, but the way I see it, copying passes ends up being more
complicated.
> IIRC the tutorial is mostly focusing on out-of-tree passes, so the steps
are different to an in-tree pass. It looks like the in-tree docs also
mostly cover out-of-tree passes (http://llvm.org/docs/WritingAnLLVMPass.html).
Improvements to the docs in that area would definitely be welcomed.

I don't necessarily want an in-tree pass and the way I see it I better
stick to:
- Old pass manager
- Out-of-tree passes

at least for now.
> Just in case you are not aware, there is already infrastructure to create
runtime checks for dependences in loops in tree:
https://github.com/llvm/llvm-project/blob/master/llvm/lib/Analysis/LoopAccessAnalysis.cpp

Yep, I know, although I have to look more into that. The thing is, I pretty
much understand all the theoretical background of DependenceAnalysis,
the way it is implemented is very clear and I somewhat can think how to
use its dependence tests to create run-time checks.
So I wanted to experiment to see how much of LoopAccessAnalysis I'll need.

Because LoopAccessAnalysis on the other hand, maybe partly because it's
focused on the loop vectorizer, is not at all clear to me. :)

Thanks for the help,
Stefanos

Στις Παρ, 22 Μαΐ 2020 στις 6:20 μ.μ., ο/η Florian Hahn <
florian_hahn at apple.com> έγραψε:
>
>
> > On May 22, 2020, at 15:42, Stefanos Baziotis via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > Hi,
> >
> > I want to create a copy of DependenceAnalysis downstream.
> >
> > At first I tried the HelloWorld tutorial. But then I figured, maybe I
> should move on
> > to create my pass by mimicking some other pass in LLVM.
> >
> > So, I tried copying DependenceAnalysis itself [1]
> >
> > Although after a lot of time of trying it compiled, I'm pretty
sure I
> have done it
> > completely in the wrong way. What is more, I can't access my pass
with
> the argument
> > I put (-rt-dep-checks).
> >
>
> For the new pass manager I think you have to add your pass to
> llvm/lib/Passes/PassRegistry.def.
>
> I’d recommend taking a look at how the DominatorTree analysis is set up.
> Also note that analysis passes on their own are invoked a little bit
> differently to transformation passes: old PM:  `opt -domtree -analyze
> foo.ll`, new PM: `opt  -passes='print<domtree>’ foo.ll`
>
> > Then, I watched this tutorial [2]. Apart from the fact that there seem
> to be
> > way too many steps just to create hello world pass, I don't think
that
> passes like
> > DependenceAnalysis follow it.
>
> IIRC the tutorial is mostly focusing on out-of-tree passes, so the steps
> are different to an in-tree pass. It looks like the in-tree docs also
> mostly cover out-of-tree passes (
> http://llvm.org/docs/WritingAnLLVMPass.html). Improvements to the docs in
> that area would definitely be welcomed.
>
>
> > [1] https://github.com/baziotis/llvm-project/tree/dep_analysis
>
> I had a quick look and it looks like your new pass is called
> RuntimeDependenceChecks.
>
> Just in case you are not aware, there is already infrastructure to create
> runtime checks for dependences in loops in tree:
>
https://github.com/llvm/llvm-project/blob/master/llvm/lib/Analysis/LoopAccessAnalysis.cpp
>
> Cheers,
> Florian
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