[llvm-dev] LLVM bc converter from LLVM 3.9 to LLVM 3.1

Tue Aug 2 19:26:43 PDT 2016

Hi Hongbin,

On Tue, Aug 2, 2016 at 5:42 PM, Jakub Kuderski <kubakuderski+llvm at gmail.com>
wrote:

> I also have a look at the code, looks like it directly parse the bitcode
>> and build in memory representation in a different LLVM version than the
>> bitcode. Is this correct?
>
> According to your description, I guess the BitCodeWriter should be the
>> one to do the bitcode version downgrade, right?
>
> I think so.
>
> I don't know much about it and don't want to give you misleading
> information; I'm cc-ing Stephen.
>
>
> On 2 August 2016 at 16:53, Hongbin Zheng <etherzhhb at gmail.com> wrote:
>
>> Thanks Jakub. Looks Like I didn't rely all.
>>
>> I also have a look at the code, looks like it directly parse the bitcode
>> and build in memory representation in a different LLVM version than the
>> bitcode. Is this correct?
>>
>
Yes, it uses a TOT reader (which can support reading all 3.x Bitcode), and
then lowers the in-memory representation back through a forked version of
the 3.2 BitcodeWriter.

>
>> According to your description, I guess the BitCodeWriter should be the
>> one to do the bitcode version downgrade, right?
>>
>
Yes, we use a separately-maintained LLVM 3.2 BticodeWriter to generate the
downgraded form. We also have 2 other BitcodeWriters based on roughly LLVM
2.9 (but not exactly 2.9, so I would steer you away from those).
https://android.googlesource.com/platform/frameworks/compile/slang/+/refs/heads/master/BitWriter_3_2/
is a link to the actual primary writer we use.

>
>>
>> Does this took work on LLVM 3.9svn?
>>
>
It currently only works up to LLVM r256229. We will most likely be updating
it to closer to TOT LLVM in the next few months, but it isn't an extreme
priority for us right now. Usually, maintenance requires us to fix up any
internal API differences that might have changed for walking/manipulating
the in-memory representation.

>
>> And could you give some hints about how you test the bitcode translator?
>>
>
We have very few tests for this, and mostly rely on older Android devices
running applications that we build using the translated bitcode. If the
older device (which only has LLVM 3.2) passes those tests, we consider it a
success. I suppose that we could take a 3.2-era BitcodeReader and wash
bitcode back and forth through it, but I don't work directly on
RenderScript these days.

One word of caution about reusing our BitcodeWriter passes - we have only
ever cared about C99, so we definitely removed some code that relates to
exception handling (and possibly some other C++-specific features). We also
only expect IR constructs that come about from normal C99
compilation/optimization, so if you have handwritten IR, there may be
unsupported instructions that we don't know how to generate legacy bitcode
for.

Thanks,
Steve

>
>> Thanks
>> Hongbin
>>
>>
>>
>>
>> On Tue, Aug 2, 2016 at 3:25 PM, Jakub Kuderski <
>> kubakuderski+llvm at gmail.com> wrote:
>>
>>> I'm not sure if it was intended, but I think that you responded only to
>>> me (not to the list).
>>>
>>> Anyway, RenderScript currently uses llvm 3.2 IR as binary
>>> representation/exchangeable format, but the llvm version is higher
>>> internally. Essentially, there it reads old bitcode and operates on the
>>> newer one in memory. When it's done, it's also able to output bitcode in
>>> the old format. The corresponding classes should be something like
>>> BitCodeReader and BitCodeWriter.
>>> The reader/writer is maintained to work with Android's llvm version,
>>> which follows upstream llvm version.
>>>
>>> I haven't worked on it myself, but if you have some specific questions,
>>> I should be able to point you to appropriate people.
>>>
>>> Regards
>>>
>>> On 2 August 2016 at 15:17, Hongbin Zheng <etherzhhb at gmail.com> wrote:
>>>
>>>> Hi Jakub,
>>>>
>>>> Thanks a lot. Do you have any document about this tool? or could you
>>>> gave me a rough idea what it do?
>>>>
>>>> Thanks
>>>> Hongbin
>>>>
>>>> On Tue, Aug 2, 2016 at 3:06 PM, Jakub Kuderski <
>>>> kubakuderski+llvm at gmail.com> wrote:
>>>>
>>>>> Hi Hongbin,
>>>>>
>>>>> Android's RenderScript uses a tool like that. You can find the sources
>>>>> here:
>>>>> https://android.googlesource.com/platform/frameworks/compile/libbcc/+/master/bcinfo/
>>>>>  .
>>>>>
>>>>> Best,
>>>>> Jakub
>>>>>
>>>>>
>>>>> On 2 August 2016 at 11:10, Hongbin Zheng via llvm-dev <
>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>
>>>>>> Hi mailing list,
>>>>>>
>>>>>> I has been working on a large project that is based on LLVM 3.1.
>>>>>> Recently we are thinking to introduce an LLVM bc converter from LLVM 3.9 to
>>>>>> LLVM 3.1, such that we can introduce some of the newest LLVM analyses and
>>>>>> optimizations to our  LLVM 3.1 based project.
>>>>>>
>>>>>> Have you worked on similar things that converting LLVM bc downward
>>>>>> and has anything to share?
>>>>>>
>>>>>> Thanks
>>>>>> Hongbin
>>>>>>
>>>>>> _______________________________________________
>>>>>> LLVM Developers mailing list
>>>>>> llvm-dev at lists.llvm.org
>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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