> On Sep 8, 2015, at 3:08 PM, Paul Robinson
> <paul_robin...@playstation.sony.com> wrote:
>
> probinson added inline comments.
>
> ================
> Comment at: lib/CodeGen/CGDebugInfo.cpp:3263-3264
> @@ +3262,4 @@
> + const NamespaceDecl *NSDecl = UD.getNominatedNamespace();
> + if (!NSDecl->isAnonymousNamespace() ||
> + CGM.getTarget().getTriple().isPS4CPU()) {
> + DBuilder.createImportedModule(
> ----------------
> rsmith wrote:
>> I think we should do this unconditionally, to better match the source
>> language semantics, but I'm curious what David, Eric, and other folks on the
>> DWARF side think.
> David (in previous discussions and review comments) has said he thinks it is
> unnecessary as the debugger already must know so much about C++ to get
> various things right, it might as well know that it has to implicitly import
> the anonymous namespace contents. One example debugger UI allows the user to
> type source-like syntax, and requires the debugger to apply (for example) C++
> parameter-type matching rules to distinguish between overloaded functions.
> Compared to this, implicit imports are child's play.
>
> I believe Eric agrees with David; I don't remember whether Adrian said
> anything in the previous iterations of this patch.
The information is redundant but otherwise harmless and there are other
compilers that emit it and debuggers that came to expect it; this makes it look
like a perfect candidate for a debugger tuning setting.
>
> I believe the explicit (although artificial) import is a good thing, because
> it matches the source language semantics. I find an important distinction
> between "which declarations are available in this scope" and "how does the
> user disambiguate declarations in this scope." As a counterpart to the above
> debugger UI example, I postulate a GUI drop-down list of symbols available
> in-scope; this UI needs to know nothing about language semantics and
> automatic imports, if the DWARF provides the correct explicit import. This
> suggests to me that the DWARF should provide it.
>
> There's also the piddly detail that debuggers are not the only consumers of
> DWARF information, and presenting the DWARF in a more source-language-neutral
> way (i.e., with the explicit artificial import) could be beneficial for those
> other consumers, who might not necessarily want to learn language-specific
> scoping rules.
>
> No debugger will be thrown for a loop if it sees the explicit import; however
> for some debuggers it would be redundant (because they implicitly import the
> anonymous namespace already). There is a pretty trivial space savings if
> it's omitted.
>
> Katya has mentioned the GCC and ICC precedent; in fairness I will say GCC
> didn't used to emit this, and GDB tolerated that.
>
> Note that the DWARF standard does not tell us what to do; it merely tells us
> how to emit the import, if we want to emit one. Whether we want to emit one
> is up to us.
Appendix D.3 does give an (albeit non-normative) example of an anonymous
top-level namespace without an explicit import.
-- adrian
>
> http://reviews.llvm.org/D12624
>
>
>
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