[cfe-commits] r50262 - in /cfe/trunk: include/clang/AST/Attr.h include/clang/Parse/AttributeList.h lib/Parse/AttributeList.cpp lib/Sema/Sema.h lib/Sema/SemaDecl.cpp

[Christopher Lamb]

Nuno,

Handling extra type attributes can be a bit complicated given that  
the type system and type conversion are core operations at the heart  
of the front-end. To implement address space qualified types has  
required adding a new wrapper type (ASQualType) and supporting this  
type throughout clang.
	
It sounds like your new type attribute may be more narrowly  
applicable to RecordTypes, but I don't think what you want can be  
solved as easily as putting the Decl's type attributes on the Type  
object itself. You can take a look at where ASQualType has been  
introduced to see how essentially adding a single attribute (address  
space) for a type, not only involves adding storage for that  
attribute in the type system, but how it must be handled robustly  
throughout the type modifications that happen in the front-end.

Thinking about adding an extra field for Record types, or a wrapper  
object for record types, are two ways of getting the information  
through to code gen. It would also be informative to see where in the  
code Record types are modified so that you could make a decision  
about how hard it will be to propagate the information through.

In all, adding such an attribute is not a quick task. I could never  
have done the ASQualType stuff in GCC, so I think there is hope. Good  
luck!
--
Chris

On Apr 25, 2008, at 2:54 AM, Nuno Lopes wrote:

> Hi,
>
> I was trying to implement the transparent_union type attribute, but  
> I think
> we need some additional API to handle it. I think we should add the
> attribute API as found in Decl to Type (i.e. addAttr(), getAttrs 
> (), ...).
> This could be used to implement this attribute and all the others type
> attributes
> (http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Type-Attributes.html).
> Alternatively we could just add an ad-hoc field to the RecordType  
> struct to
> record if it's a transparent union or not, which also makes sense.
>
> Please give me some feedback.
>
> Thanks,
> Nuno
>
>
>> URL: http://llvm.org/viewvc/llvm-project?rev=50262&view=rev
>> Log:
>> initial support for recognizing __transparent_union__ attributes
>> comments on the ML will follow
>> ===================================================================== 
>> =========
>> --- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
>> +++ cfe/trunk/lib/Sema/SemaDecl.cpp Fri Apr 25 04:32:00 2008
>> @@ -2419,6 +2422,29 @@
>>                             Idx.getZExtValue(),  
>> FirstArg.getZExtValue()));
>> }
>>
>> +void Sema::HandleTransparentUnionAttribute(Decl *d, AttributeList
>> *rawAttr) {
>> +  // check the attribute arguments.
>> +  if (rawAttr->getNumArgs() != 0) {
>> +    Diag(rawAttr->getLoc(),  
>> diag::err_attribute_wrong_number_arguments,
>> +         std::string("0"));
>> +    return;
>> +  }
>> +
>> +  TypeDecl *decl = dyn_cast<TypeDecl>(d);
>> +
>> +  if (!decl || !Context.getTypeDeclType(decl)->isUnionType()) {
>> +    Diag(rawAttr->getLoc(), diag::warn_attribute_wrong_decl_type,
>> +         "transparent_union", "union");
>> +    return;
>> +  }
>> +
>> +  QualType QTy = Context.getTypeDeclType(decl);
>> +  const RecordType *Ty = QTy->getAsUnionType();
>> +
>> +// FIXME
>> +// Ty->addAttr(new TransparentUnionAttr());
>> +}
>> +
>
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--
Christopher Lamb



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