llvm dev - Sep 2016 - Adding utility/debugging passes upstream

Hi,

I was wondering what’s the community guideline for adding new passes which are
solely used for debugging/analysis purposes? Can this be in the upstream llvm,
or such passes are more suitable in local downstream repository?

In our case, the ‘utility (ease-of-analysis)’ pass is for transformation done by
RewriteStatepointsForGC (RS4GC). Note that right now, RS4GC is not enabled in
the opt pipeline upstream, but the utility pass would be for downstream users
who have RS4GC enabled in their opt pipeline.


Thanks,
Anna

> On Sep 30, 2016, at 12:37 PM, Anna Thomas via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hi,
> 
> I was wondering what’s the community guideline for adding new passes which
are solely used for debugging/analysis purposes? Can this be in the upstream
llvm, or such passes are more suitable in local downstream repository?
> 
> In our case, the ‘utility (ease-of-analysis)’ pass is for transformation
done by RewriteStatepointsForGC (RS4GC). Note that right now, RS4GC is not
enabled in the opt pipeline upstream, but the utility pass would be for
downstream users who have RS4GC enabled in their opt pipeline.
I think you should start by describing exactly what the pass is doing and how it
is useful for working with/on RewriteStatepointsForGC.

If it is correctly tested and documented, I don’t see why it couldn’t be
in-tree.

— 
Mehdi

Hi Mehdi,

On Sep 30, 2016, at 4:27 PM, Mehdi Amini <mehdi.amini at
apple.com<mailto:mehdi.amini at apple.com>> wrote:


On Sep 30, 2016, at 12:37 PM, Anna Thomas via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:

Hi,

I was wondering what’s the community guideline for adding new passes which are
solely used for debugging/analysis purposes? Can this be in the upstream llvm,
or such passes are more suitable in local downstream repository?

In our case, the ‘utility (ease-of-analysis)’ pass is for transformation done by
RewriteStatepointsForGC (RS4GC). Note that right now, RS4GC is not enabled in
the opt pipeline upstream, but the utility pass would be for downstream users
who have RS4GC enabled in their opt pipeline.

I think you should start by describing exactly what the pass is doing and how it
is useful for working with/on RewriteStatepointsForGC.
The pass will remove all the gc.relocates that are inserted by
RewriteStatepoints. This is solely useful for analysis purposes of the final
optimized IR (with RS4GC in place), when the IR is too polluted with
gc.relocates of the original pointers.

More details at: https://reviews.llvm.org/D25096

The scenario where this is useful: There is a performance regression and
analyzing through the final IR is too tedious because of all the gc.relocates.
This pass would take the optimized IR, and remove the gc.relocates. This will
enable easier manual traversal through IR (without having to worry about the
gc.relocates).


If it is correctly tested and documented, I don’t see why it couldn’t be
in-tree.

Yes, agreed.

—
Mehdi


Thanks,
Anna

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