llvm dev - Sep 2020 - LLVM Developers Meeting JIT BoF -- Request for Topics of Interest

Hi Andres,

A topic that I'd find interesting is what it'd take to make it easier
to
> use profile guided optimization in the context of JIT.  A few years back
> I crudely hacked this together, but it was fairly ugly. It'd be nice to
> make that easier.  Possibly too complicated for that type of session?

We couldn't go into detail, but we could kick off a discussion and identify
who is interested in working on this. My pitch: We should solve this
by investing in JITLink and implementing profiling (and debugger support)
via ObjectLinkingLayer::Plugins. Maybe a brief overview of / discussion on
how these work would be useful?

-- Lang.


On Fri, Sep 25, 2020 at 7:19 PM Andres Freund <andres at anarazel.de>
wrote:
> Hi,
>
> On 2020-09-25 19:05:42 -0700, Lang Hames wrote:
> > The 2020 Virtual LLVM Developer's Meeting is coming up the week
after
> next.
> > I'll be hosting a JIT Birds-of-a-Feather session on Thursday the
8th at
> > 10:55am PDT (See http://llvm.org/devmtg/2020-09/schedule/). I'm
> planning to
> > run this more like a Round Table: Minimal introduction, plenty of time
> for
> > discussion.
> >
> > Does anyone have any LLVM JIT related topics that they would
particularly
> > like to discuss at this session? Any questions that they think could
be
> > best answered by a round-table style discussion? I'll aim to rope
in the
> > right people and prepare answers to make sure we get the most out of
the
> > session.
>
> A topic that I'd find interesting is what it'd take to make it
easier to
> use profile guided optimization in the context of JIT.  A few years back
> I crudely hacked this together, but it was fairly ugly. It'd be nice to
> make that easier.  Possibly too complicated for that type of session?
>
> I dimly recall that the main issue was that there is no good way to
> extract the profile information without going through files / applying
> the profile data without going through files.
>
> Greetings,
>
> Andres Freund
>
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Importing symbols into the JIT from an object file or static library...?

On Mon, Sep 28, 2020 at 5:29 AM Lang Hames <lhames at gmail.com> wrote:
> Hi Andres,
>
> A topic that I'd find interesting is what it'd take to make it
easier to
>> use profile guided optimization in the context of JIT.  A few years
back
>> I crudely hacked this together, but it was fairly ugly. It'd be
nice to
>> make that easier.  Possibly too complicated for that type of session?
>
>
> We couldn't go into detail, but we could kick off a discussion and
> identify who is interested in working on this. My pitch: We should solve
> this by investing in JITLink and implementing profiling (and debugger
> support) via ObjectLinkingLayer::Plugins. Maybe a brief overview of /
> discussion on how these work would be useful?
>
> -- Lang.
>
>
> On Fri, Sep 25, 2020 at 7:19 PM Andres Freund <andres at anarazel.de>
wrote:
>
>> Hi,
>>
>> On 2020-09-25 19:05:42 -0700, Lang Hames wrote:
>> > The 2020 Virtual LLVM Developer's Meeting is coming up the
week after
>> next.
>> > I'll be hosting a JIT Birds-of-a-Feather session on Thursday
the 8th at
>> > 10:55am PDT (See http://llvm.org/devmtg/2020-09/schedule/).
I'm
>> planning to
>> > run this more like a Round Table: Minimal introduction, plenty of
time
>> for
>> > discussion.
>> >
>> > Does anyone have any LLVM JIT related topics that they would
>> particularly
>> > like to discuss at this session? Any questions that they think
could be
>> > best answered by a round-table style discussion? I'll aim to
rope in the
>> > right people and prepare answers to make sure we get the most out
of the
>> > session.
>>
>> A topic that I'd find interesting is what it'd take to make it
easier to
>> use profile guided optimization in the context of JIT.  A few years
back
>> I crudely hacked this together, but it was fairly ugly. It'd be
nice to
>> make that easier.  Possibly too complicated for that type of session?
>>
>> I dimly recall that the main issue was that there is no good way to
>> extract the profile information without going through files / applying
>> the profile data without going through files.
>>
>> Greetings,
>>
>> Andres Freund
>>
>
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Hi Geoff,

Importing symbols into the JIT from an object file or static library...?


Sure! Are you interested in doing this with the C API, LLJIT, or raw OrcV2
components?

The high-level answer here (which we can dig into further in the BoF) is:

For object files:
- For raw OrcV2 components you'll want to create an
RTDyldObjectLinkingLayer or ObjectLinkingLayer and use the 'add' method.
- For an LLJIT instance you can just call the 'addObjectFile' method.
- For the OrcV2 C API you can call the 'LLVMOrcLLJITAddObjectFile'
function.

For static libraries:
- For raw OrcV2 components or an LLJIT instance you can attach a
StaticLibraryDefinitionGenerator [1] to the JITDylib that you would like to
load the library into. See [2] for an example.
- For the OrcV2 C API we will just need to add a method to wrap the
operation above. We already have
'LLVMOrcCreateDynamicLibrarySearchGeneratorForProcess'. We should add
counterparts to that to load dynamic and static libraries from paths.

-- Lang.

[1]
https://github.com/llvm/llvm-project/blob/5aa56b242951ab0f0181386ea58509f19b09206e/llvm/include/llvm/ExecutionEngine/Orc/ExecutionUtils.h#L361
[2]
https://github.com/llvm/llvm-project/blob/e7549dafcd33ced4280a81ca1d1ee4cc78ed253f/llvm/tools/lli/lli.cpp#L968


On Mon, Sep 28, 2020 at 7:18 AM Geoff Levner <glevner at gmail.com> wrote:
> Importing symbols into the JIT from an object file or static library...?
>
> On Mon, Sep 28, 2020 at 5:29 AM Lang Hames <lhames at gmail.com>
wrote:
>
>> Hi Andres,
>>
>> A topic that I'd find interesting is what it'd take to make it
easier to
>>> use profile guided optimization in the context of JIT.  A few years
back
>>> I crudely hacked this together, but it was fairly ugly. It'd be
nice to
>>> make that easier.  Possibly too complicated for that type of
session?
>>
>>
>> We couldn't go into detail, but we could kick off a discussion and
>> identify who is interested in working on this. My pitch: We should
solve
>> this by investing in JITLink and implementing profiling (and debugger
>> support) via ObjectLinkingLayer::Plugins. Maybe a brief overview of /
>> discussion on how these work would be useful?
>>
>> -- Lang.
>>
>>
>> On Fri, Sep 25, 2020 at 7:19 PM Andres Freund <andres at
anarazel.de> wrote:
>>
>>> Hi,
>>>
>>> On 2020-09-25 19:05:42 -0700, Lang Hames wrote:
>>> > The 2020 Virtual LLVM Developer's Meeting is coming up the
week after
>>> next.
>>> > I'll be hosting a JIT Birds-of-a-Feather session on
Thursday the 8th at
>>> > 10:55am PDT (See http://llvm.org/devmtg/2020-09/schedule/).
I'm
>>> planning to
>>> > run this more like a Round Table: Minimal introduction, plenty
of time
>>> for
>>> > discussion.
>>> >
>>> > Does anyone have any LLVM JIT related topics that they would
>>> particularly
>>> > like to discuss at this session? Any questions that they think
could be
>>> > best answered by a round-table style discussion? I'll aim
to rope in
>>> the
>>> > right people and prepare answers to make sure we get the most
out of
>>> the
>>> > session.
>>>
>>> A topic that I'd find interesting is what it'd take to make
it easier to
>>> use profile guided optimization in the context of JIT.  A few years
back
>>> I crudely hacked this together, but it was fairly ugly. It'd be
nice to
>>> make that easier.  Possibly too complicated for that type of
session?
>>>
>>> I dimly recall that the main issue was that there is no good way to
>>> extract the profile information without going through files /
applying
>>> the profile data without going through files.
>>>
>>> Greetings,
>>>
>>> Andres Freund
>>>
>>
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