[LLVMdev] String attributes for function arguments and return values
Philip Reames
listmail at philipreames.com
Tue Jul 14 21:42:46 PDT 2015
On 07/14/2015 09:09 PM, Eric Christopher wrote:
>
>
> On Tue, Jul 14, 2015 at 9:01 PM Philip Reames
> <listmail at philipreames.com <mailto:listmail at philipreames.com>> wrote:
>
> On 07/14/2015 05:07 PM, Pete Cooper wrote:
>>
>>> On Jul 14, 2015, at 4:48 PM, Reid Kleckner <rnk at google.com
>>> <mailto:rnk at google.com>> wrote:
>>>
>>> This sounds more like a use case for metadata. Can we attach
>>> metadata to function arguments, or does that not work currently?
>> We can’t, no.
>>
>> I have an out of tree patch which allows metadata in
>> AttributeSets. This would also potentially also work here.
>>
>> However, depending on the number of unique strings/metadata in
>> AttributeSets, this could get large. I don’t think we’ve ever
>> had more that a few unique AttributeSets in an entire module. If
>> you have too many different strings then you could have a
>> significant number of sets which could get slow.
>>
>> Metadata attached to the function or the function arguments is
>> likely to scale better than strings/metadata in the
>> AttributeSets, but I guess it all depends on whether many are
>> even needed.
> As far as I can tell, the string attributes on function parameters
> is already "supposed to work". We support it in bytecode. We
> even support serialization of the attributes. It's just the
> parsing that's broken. I don't have any problem with an eventual
> move towards supporting metadata on arguments, but does anyone
> object to landing the current patches? Whether we believe that the
> use case motivating the patch is better represented by metadata or
> not, having the deserialization support seems like a clear
> improvement.
>
> As a side note, I can't find any mention of the string attribute
> functionality in the LangRef or ExtendingLLVM. Seems like it might
> be time to add something about the capability for extension. We
> should probably also *explicitly* reserve the entire namespace of
> possible keywords for future LLVM in tree enhancements.
>
>
> So as far as the attribute versus metadata question here I don't have
> a particular care whether or not we support attributes on any
> particular thing in the Value hierarchy. As far as your particular
> case I really only have one question: are the attributes needed for
> correctness or for optimization? If they're the latter they should
> probably be metadata, the former then attributes seem to make the best
> sense.
For the particular use case we have, metadata on arguments would be a
better semantic fit. It's a pure optimization hint. Having said that,
attributes work just fine in practice as well.
>
> Mostly just trying to see about you getting the right fixes in for the
> support you need and the rest of us not having to worry about not
> breaking things that no one cares about :)
Let me restate my previous comment: Having support for custom attributes
on function arguments is generally useful for external users of LLVM.
Whether it is ideal in this particular case is not really relevant.
There are certainly reasonable cases where using a target/environment
specific attribute to effect call lowering makes perfect sense. It
seems desireable to be able to prototype these quickly so that they can
mature and (possibly) make it upstream.
My view is that we *already* support these attributes. I don't have an
example user, but it really wouldn't surprise me if folks were using
this functionality already. Everything works if generated through the
C++ APIs or read from bitcode. It's only the deserialization parts that
break. In particular, you can have a working compiler which generates
output which isn't parseable by LLVM's existing tools. That's not
exactly a good state to be in.
>
> -eric
>
>
> Philip
>
>>>
>>> On Mon, Jul 13, 2015 at 7:42 AM, Artur Pilipenko
>>> <apilipenko at azulsystems.com <mailto:apilipenko at azulsystems.com>>
>>> wrote:
>>>
>>> Hi,
>>>
>>>> On 13 Jul 2015, at 15:59, Hal Finkel <hfinkel at anl.gov
>>>> <mailto:hfinkel at anl.gov>> wrote:
>>>>
>>>> ----- Original Message -----
>>>>> From: "Artur Pilipenko" <apilipenko at azulsystems.com
>>>>> <mailto:apilipenko at azulsystems.com>>
>>>>> To:llvmdev at cs.uiuc.edu <mailto:llvmdev at cs.uiuc.edu>
>>>>> Cc: "Hal Finkel" <hfinkel at anl.gov <mailto:hfinkel at anl.gov>>
>>>>> Sent: Monday, July 13, 2015 6:45:35 AM
>>>>> Subject: String attributes for function arguments and
>>>>> return values
>>>>>
>>>>> Hi,
>>>>>
>>>>> I’d like to support string attributes on function
>>>>> arguments and
>>>>> return values. We are going to use them in our tree to express
>>>>> higher level language types.
>>>>
>>>> How do you expect to use this information? Will you need
>>>> the inliner to do something special with these?
>>> Type information is required for Java specific
>>> optimizations, like devirtualization, subtype check
>>> optimizations, etc. There are no plans to upstream them,
>>> because they are too specific to Java.
>>>
>>> W.r.t inlining I don’t think that these attributes will
>>> require any special handling.
>>>
>>> Artur
>>>
>>>>
>>>> Thanks again,
>>>> Hal
>>>>
>>>>>
>>>>> Internally attributes framework have everything to do
>>>>> this, it’s even
>>>>> possible to generate string attributes via API right now:
>>>>> Function *function;
>>>>> function->setAttributes(function->getAttributes().addAttribute(context,
>>>>> i, "attribute"));
>>>>> But because it’s not supported in LLParser if you dump the
>>>>> function
>>>>> and try to parse it back it will fail. I have a patch to
>>>>> fix this
>>>>> problem:
>>>>> http://reviews.llvm.org/D11058
>>>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_D11058&d=AwMGaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=Mfk2qtn1LTDThVkh6-oGglNfMADXfJdty4_bhmuhMHA&m=QxcZ1dQY-4Fptsg8J_QZvUH5zX3_zJfFtYe_mFFV434&s=yDXYh5H5eycn3Yn6A7bDimwo8jVbqaGav2FdRRIz0lg&e=>
>>>>> I consider this part as a bug fix for existing functionality.
>>>>>
>>>>> The second patch is to add accessors to string attributes
>>>>> to Argument
>>>>> and Function classes:
>>>>> http://reviews.llvm.org/D10872
>>>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_D10872&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=Mfk2qtn1LTDThVkh6-oGglNfMADXfJdty4_bhmuhMHA&m=x-SxyqtoLVC9ndWtSNBJBeyYQml3MZ2Ch4L_B4Hc3Yg&s=a-NOt0poEqPq0I1bAMlsGTKRbxjviviAhMjJ41PNN2Y&e=>
>>>>> This part is optional because there no code in upstream
>>>>> will make use
>>>>> of it. But if we support string attributes syntax it makes
>>>>> sense to
>>>>> provide API support as well.
>>>>>
>>>>> Does anyone have any objections?
>>>>>
>>>>> Thanks,
>>>>> Artur
>>>>>
>>>>>
>>>>>
>>>>
>>>> --
>>>> Hal Finkel
>>>> Assistant Computational Scientist
>>>> Leadership Computing Facility
>>>> Argonne National Laboratory
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu>
>>> http://llvm.cs.uiuc.edu <http://llvm.cs.uiuc.edu/>
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu>
>>> http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu> http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu>
> http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150714/fae0f469/attachment.html>
More information about the llvm-dev
mailing list