[llvm-dev] [RFC] Moving tools/llvm-mca/lib into lib/MCA

[Greg Bedwell via llvm-dev]

Makes sense to me.  Should CODE_OWNERS.TXT also be updated to reflect the
move too?

On Wed, 12 Dec 2018 at 12:52, Andrea Di Biagio <andrea.dibiagio at gmail.com>
wrote:

> Thanks Clement for working on this.
>
> I like the idea of moving the core abstractions of llvm-mca in llvm/lib,
> as it potentially enables a number of interesting use cases and future
> developments.
>
> As you wrote, the patch is very simple (a pretty mechanical change).
> From my point of view, this all looks good. Let see if other people have
> the same opinion on this.
>
> -Andrea
>
>
> On Wed, Dec 12, 2018 at 11:58 AM Clement Courbet <courbet at google.com>
> wrote:
>
>> (on the correct mailing list)
>>
>>
>> Hi all,
>>
>> tl;dr: We'd like to propose moving tools/llvm-mca/lib into lib/MCA and
>> create a new MCA library in LLVM.
>>
>> llvm-mca has recently been split
>> <https://bugs.llvm.org/show_bug.cgi?id=37696> into its core part and the
>> tool part.
>>
>>    -
>>
>>    The core part simulates the execution of a basic block of machine
>>    instructions as modeled by the llvm SchedModel.
>>    -
>>
>>    The tool part deals with the plumbing and interacting with the user.
>>
>>
>> The core part can be used by parts of LLVM that deal with cost modeling
>> (e.g. scheduling and vectorization). MCA provides a more realistic target
>> for optimization than the heuristics typically used to drive these passes.
>> We think that using approaches based on fine-grained cost modeling can
>> greatly improve the performance of critically hot code, by trading compile
>> time for performance.
>>
>> As an example of how MCA can be used to improve scheduling, we have built
>> a prototype machine scheduler that optimizes the simulated latency of a
>> block of code under the constraints of the scheduling DAG. We've had
>> interesting wins of 2-3% on assembly kernels for webp
>> <https://github.com/webmproject/libwebp/commit/67748b41dbb21a43e88f2b6ddf6117f4338873a3>
>> and gemmlowp <https://github.com/google/gemmlowp/pull/91>*.
>>
>> The patch is completely mechanical and can be seen here
>> <https://reviews.llvm.org/D55557>. It only moves the files and updates
>> all references.
>>
>> We'd like to hear if there are any things comments/objections to this
>> change.
>>
>> Thanks !
>>
>> *note: We did this before llvm-mca was released and were using a
>> different simulator, but the idea remains the same.
>>
>> On Wed, Dec 12, 2018 at 11:44 AM Clement Courbet <courbet at google.com>
>> wrote:
>>
>>> Hi all,
>>>
>>> tl;dr: We'd like to propose moving tools/llvm-mca/lib into lib/MCA and
>>> create a new MCA library in LLVM.
>>>
>>> llvm-mca has recently been split
>>> <https://bugs.llvm.org/show_bug.cgi?id=37696> into its core part and
>>> the tool part.
>>>
>>>    -
>>>
>>>    The core part simulates the execution of a basic block of machine
>>>    instructions as modeled by the llvm SchedModel.
>>>    -
>>>
>>>    The tool part deals with the plumbing and interacting with the user.
>>>
>>>
>>> The core part can be used by parts of LLVM that deal with cost modeling
>>> (e.g. scheduling and vectorization). MCA provides a more realistic target
>>> for optimization than the heuristics typically used to drive these passes.
>>> We think that using approaches based on fine-grained cost modeling can
>>> greatly improve the performance of critically hot code, by trading compile
>>> time for performance.
>>>
>>> As an example of how MCA can be used to improve scheduling, we have
>>> built a prototype machine scheduler that optimizes the simulated latency of
>>> a block of code under the constraints of the scheduling DAG. We've had
>>> interesting wins of 2-3% on assembly kernels for webp
>>> <https://github.com/webmproject/libwebp/commit/67748b41dbb21a43e88f2b6ddf6117f4338873a3>
>>> and gemmlowp <https://github.com/google/gemmlowp/pull/91>*.
>>>
>>> The patch is completely mechanical and can be seen here
>>> <https://reviews.llvm.org/D55557>. It only moves the files and updates
>>> all references.
>>>
>>> We'd like to hear if there are any things comments/objections to this
>>> change.
>>>
>>> Thanks !
>>>
>>> *note: We did this before llvm-mca was released and were using a
>>> different simulator, but the idea remains the same.
>>>
>>>
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