[PATCH] align_value attribute in Clang

[Bataev, Alexey]

Hi Hal,
I'm not sure is it a proper solution, but I would try just to propagate 
this attribute on auto type deduction. Adding a new type will take a lot 
of time, though it is more perspective in terms of future extension for 
the new similar attributes.

Best regards,
Alexey Bataev
=============
Software Engineer
Intel Compiler Team

18.09.2014 3:25, Hal Finkel пишет:
> ----- Original Message -----
>> From: "Hal Finkel" <hfinkel at anl.gov>
>> To: reviews+D4635+public+b7e82bdc1d8c324a at reviews.llvm.org
>> Cc: "a bataev" <a.bataev at hotmail.com>, "nurmukhametov alex" <nurmukhametov.alex at gmail.com>, "aaron ballman"
>> <aaron.ballman at gmail.com>, richard at metafoo.co.uk, cfe-commits at cs.uiuc.edu
>> Sent: Monday, September 8, 2014 6:59:07 PM
>> Subject: Re: [PATCH] align_value attribute in Clang
>>
>> ----- Original Message -----
>>> From: hfinkel at anl.gov
>>> To: hfinkel at anl.gov, "aaron ballman" <aaron.ballman at gmail.com>,
>>> bigcheesegs at gmail.com, richard at metafoo.co.uk, "a
>>> bataev" <a.bataev at hotmail.com>
>>> Cc: cfe-commits at cs.uiuc.edu, "nurmukhametov alex"
>>> <nurmukhametov.alex at gmail.com>
>>> Sent: Monday, September 8, 2014 6:38:44 PM
>>> Subject: Re: [PATCH] align_value attribute in Clang
>>>
>>> Rebased, and removed from inappropriate
>>> isTypeDependent/isValueDependent checks (inappropriate here for the
>>> same reason they were inappropriate in patch D4601 for the
>>> assume_aligned attribute).
>>>
>>> Work still needs to be done to allow use as a type attribute (so
>>> that
>>> the attribute follows type deduction, auto, etc.). I'll send a
>>> follow-up e-mail about this with questions.
> Pinging re: the design question below.
>
> Thanks again,
> Hal
>
>> I need this attribute to follow type deduction (auto, etc.), and as
>> we've discussed, just making this a declaration attribute does not
>> seem to do this. It seems to me that what I need to do, or at least
>> might do, is hook align_value into AttributedType, and handle it in
>> lib/Sema/SemaType.cpp. First, it is not clear where I should store
>> the alignment parameter:
>>    - address_space stores its value in the type qualifiers
>>    - reg_parm stores its value as part of FunctionType
>>    - vector_type / ext_vector_type are their own Type subclasses
>>    (where ExtVectorType is a subclass of VectorType, but there is
>>    also DependentSizedExtVectorType which handles dependent
>>    attributes).
>>
>> Given that align_value also needs to handle dependent alignment
>> values, that seems most like the
>> ExtVectorType/DependentSizedExtVectorType setup. I could create
>> AlignValuePointerType/DependentAlignValuePointerType (or similar),
>> maybe with AlignValuePointerType being a subclass of PointerType?
>> (or maybe both being subclasses of PointerType?)
>>
>> That having been said, creating subclasses of PointerType and/or new
>> Type subclasses seems like an unfortunate amount of infrastructure
>> for this feature. An alternative would be to place extra data
>> directly into PointerType, but I don't like that idea because it
>> adds memory (and some runtime) overhead to the common case with no
>> corresponding benefit.
>>
>> Ideally, I'd be able to use the original AlignValueAttr nodes,
>> perhaps in combination with AttributedType somehow to indicate that
>> a relevant AlignValueAttr node exists somewhere. Is there a way to
>> do this?
>>
>> In short, I'm not sure what the best way of doing this is, and I'm
>> looking for advice.
>>
>> Thanks again,
>> Hal
>>
>>> http://reviews.llvm.org/D4635
>>>
>>> Files:
>>>    include/clang/Basic/Attr.td
>>>    include/clang/Basic/AttrDocs.td
>>>    include/clang/Basic/DiagnosticSemaKinds.td
>>>    include/clang/Sema/AttributeList.h
>>>    include/clang/Sema/Sema.h
>>>    lib/CodeGen/CGCall.cpp
>>>    lib/Sema/SemaDeclAttr.cpp
>>>    lib/Sema/SemaTemplateInstantiateDecl.cpp
>>>    test/CodeGen/align_value.cpp
>>>    test/Sema/align_value.c
>>>    test/SemaCXX/align_value.cpp
>>>
>> --
>> Hal Finkel
>> Assistant Computational Scientist
>> Leadership Computing Facility
>> Argonne National Laboratory
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