[llvm-dev] LLVM Developers Meeting JIT BoF -- Request for Topics of Interest

[Lang Hames via llvm-dev]

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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