[PATCH] D7895: Anonymous namespaces are missing import DW_TAG_imported_module.

[Robinson, Paul via llvm-commits]

DWARF describes a mapping from source to object.  It tries to use language-neutral mechanisms to do this.  "Namespace" is not a C++-specific notion.  "Importing" a name or set of names from one scope to another is not a C++-specific notion.  Emitting an artificial import seems like a perfectly natural way to translate the C++ language-specific rule about anonymous namespaces into a language-neutral DWARF description.

This is not about how to let a user identify an entity available within a scope; this is about what entities are available within the scope in the first place.  The artificial import gives you that.  Failing to provide the import imposes a *requirement* on the client to understand language-specific scope-munging rules, in order for the client to even know what entities are available.  DWARF tries hard not to impose that kind of requirement.  (DWARF does assume that inner scopes can see all entities in outer scopes, which is how most but not all languages work.  COBOL's data-visibility rules are really arcane.)

Regarding ADL, it is not a DWARF-imposed requirement that every debug-info client understand all the C++-defined shorthand methods for identifying an entity.  While could be very user-friendly of the client to permit users to type in C++-like syntax to name things, and disambiguate them for you, that depends on the client's UI and at most is a quality-of-implementation issue for the client, not something assumed or imposed (and certainly not required) by DWARF.

Regarding calling conventions, a lot of the relevant information is actually explicit in the DWARF, and (without having thought about it much) I expect what's implicit would be platform-dependent not language-dependent.  Clients *are* expected to understand the target platform.

To recap: An artificial import of a C++ anonymous namespace conforms to DWARF's intent, and having it be target-dependent is silly.
--paulr

From: David Blaikie [mailto:dblaikie at gmail.com]
Sent: Monday, August 17, 2015 6:16 PM
To: reviews+D7895+public+7827be49c0b04087 at reviews.llvm.org; Robinson, Paul
Cc: Romanova, Katya; Eric Christopher; Frédéric Riss; Duncan P. N. Exon Smith; llvm-commits
Subject: Re: [PATCH] D7895: Anonymous namespaces are missing import DW_TAG_imported_module.



On Mon, Aug 17, 2015 at 6:12 PM, Paul Robinson via llvm-commits <llvm-commits at lists.llvm.org<mailto:llvm-commits at lists.llvm.org>> wrote:
probinson added a comment.

I don't think this should be PS4-special.  I know I was more wishy-washy about it before, but really DWARF-the-standard tries to be language-neutral.  Emitting an explicit import matches the intent of DWARF, and Clang should always do it.

I don't quite see how "DWARF the standard tries to be language neutral" and "DWARF should model the source" are resolved here... the source is an anonymous namespace, without any using directive. In the same way that DWARF clients figure out calling conventions (and name lookup rules for other entities - including complex things like ADL) based on the language, so would this, I would think.



http://reviews.llvm.org/D7895



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