[LLVMdev] [NVPTX] llc -march=nvptx64 -mcpu=sm_20 generates invalid zero align for device function params

[Dmitry N. Mikushin]

Hi Justin,

Very glad you're finally back! How's you PhD?

Please see the attached updated patch. Since you think ABI is better,
I'm only adding a test case.

- D.

2012/11/9 Justin Holewinski <justin.holewinski at gmail.com>:
> Test cases exist under test/CodeGen/NVPTX (name changed in May).  Now that
> I'm back at NVIDIA, I'm going to be running through the bugzilla issues
> (thanks Dmitry for the reports!).  I have practically the exact same patch
> here in my queue. :)
>
> In this case, I would prefer ABI alignment for compatibility with the vendor
> compiler.  It should work either way, but I do need to audit the codebase
> and tie up any issues here.
>
>
> On Fri, Nov 9, 2012 at 5:23 AM, Duncan Sands <baldrick at free.fr> wrote:
>>
>> Hi Dmitry,
>>
>>
>>> You're right, global variables use preferred alignment. And - yes,
>>> preferred alignment in this case is bigger: 8 instead of 4. NVIDIA's
>>> prop. compiler gives 4. However, since CUDA 5.0 ptx modules are
>>> linkable with each other, I think alignments for externally visible
>>> functions and data should all follow ABI rules.
>>
>>
>> giving it an alignment of 8 does follow ABI rules: everything that is
>> 8 byte aligned has an address that is a multiple of 4, i.e. it is also
>> 4 byte aligned.
>>
>> It would be wrong to assume that external globals have the preferred
>> alignment: they can only be assumed to have the ABI alignment.  But
>> as we are aligning this variable we can give it the alignment we like
>> as long as it is at least 4.
>>
>> In short, I think using the preferred alignment is correct in this
>> context.
>>
>>
>>> Is there a guide on making tests? I have ~5 pending patches never
>>> accepted simply because I'm not familiar with LLVM test system :-/
>>
>>
>> Your test would go in test/CodeGen/PTX/.  It should use FileCheck,
>> take a look at test/CodeGen/X86/zext-trunc.ll for an example.  As
>> there are no PTX tests at all for the moment, you need to create a
>> lit.local.cfg file in PTX/.  Imitate the X86 one.
>>
>> Ciao, Duncan.
>>
>>
>>>
>>> - D.
>>>
>>> 2012/11/9 Duncan Sands <baldrick at free.fr>:
>>>>
>>>> Hi Dmitry,
>>>>
>>>>
>>>>> I'm attaching a patch that should fix the issue mentioned above. It
>>>>>
>>>>> simply makes the same check seen in the same file for global
>>>>> variables:
>>>>>
>>>>>     emitPTXAddressSpace(PTy->getAddressSpace(), O);
>>>>>     if (GVar->getAlignment() == 0)
>>>>>       O << " .align " << (int) TD->getPrefTypeAlignment(ETy);
>>>>>     else
>>>>>       O << " .align " << GVar->getAlignment();
>>>>
>>>>
>>>>
>>>> it's not quite the same because your patch uses the ABI alignment, while
>>>> in this snippet it is the preferred alignment (which is usually the same
>>>> as the ABI alignment, but may be bigger).
>>>>
>>>>
>>>>> Could you please review and commit? Do you think it needs a test case?
>>>>
>>>>
>>>>
>>>> Yes, it needs a testcase.
>>>>
>>>> Ciao, Duncan.
>>>>
>>>> _______________________________________________
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>>
>>
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>
>
>
>
> --
>
> Thanks,
>
> Justin Holewinski
>
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