r253012 - [modules] When a declaration has non-trivial visibility, check whether it's

[Sean Silva via cfe-commits]

On Mon, Nov 16, 2015 at 7:09 PM, Richard Smith <richard at metafoo.co.uk>
wrote:

> On Mon, Nov 16, 2015 at 7:00 PM, Sean Silva <chisophugis at gmail.com> wrote:
>
>> On Sat, Nov 14, 2015 at 2:30 PM, Richard Smith <richard at metafoo.co.uk>
>> wrote:
>>
>>> On Nov 13, 2015 7:23 PM, "Sean Silva" <chisophugis at gmail.com> wrote:
>>> >
>>> >
>>> >
>>> > On Thu, Nov 12, 2015 at 9:14 PM, Richard Smith via cfe-commits <
>>> cfe-commits at lists.llvm.org> wrote:
>>> >>
>>> >> Author: rsmith
>>> >> Date: Thu Nov 12 23:14:45 2015
>>> >> New Revision: 253012
>>> >>
>>> >> URL: http://llvm.org/viewvc/llvm-project?rev=253012&view=rev
>>> >> Log:
>>> >> [modules] When a declaration has non-trivial visibility, check
>>> whether it's
>>> >
>>> >
>>> > What is "non-trivial visibility"? Is this "visibility" something that
>>> exists in the present C++ language? (e.g. `using namespace std` etc.) or is
>>> this a different notion?
>>>
>>> This is the modules notion of visibility (whether the declaration has
>>> been imported or not). Here, non-trivial visibility means "not known to be
>>> unconditionally visible", and corresponds to the Hidden flag on the Decl
>>> being true.
>>>
>>
>> I just looked at the comment on the `Hidden` flag and it doesn't seem to
>> mention anything about being "trivial" or "non-trivial". Why say
>> "declaration has non-trivial visibility" instead of just "declaration is
>> hidden"? Do they mean different things?
>>
>
> Yes; the comment on that flag is out of date. Whether a declaration is
> visible is a function of several factors and isn't as simple as checking
> that flag. When performing template instantiation, names from unimported
> modules (and module-private names from imported modules) can be made
> visible if they were visible when the template was defined. When local
> submodule visibility is enabled, the visibility of a declaration is
> computed each time we reference it, because module visibility is not
> monotonically increasing.
>

Ah, that makes sense. Also that sounds scary complicated.

-- Sean Silva


>
> If the Hidden flag is false, the declararation is unconditionally visible.
> If the Hidden flag is true, the declaration might still be visible,
> depending on who's asking and from where.
>
>
>> -- Sean Silva
>>
>>
>>> > -- Sean Silva
>>> >
>>> >>
>>> >> actually hidden before we check its linkage. This avoids computing
>>> the linkage
>>> >> "too early" for an anonymous struct with a typedef name for linkage.
>>> >>
>>> >> Modified:
>>> >>     cfe/trunk/include/clang/Sema/Lookup.h
>>> >>     cfe/trunk/test/Modules/submodule-visibility.cpp
>>> >>
>>> >> Modified: cfe/trunk/include/clang/Sema/Lookup.h
>>> >> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/Lookup.h?rev=253012&r1=253011&r2=253012&view=diff
>>> >>
>>> ==============================================================================
>>> >> --- cfe/trunk/include/clang/Sema/Lookup.h (original)
>>> >> +++ cfe/trunk/include/clang/Sema/Lookup.h Thu Nov 12 23:14:45 2015
>>> >> @@ -303,8 +303,7 @@ public:
>>> >>      if (!D->isInIdentifierNamespace(IDNS))
>>> >>        return nullptr;
>>> >>
>>> >> -    if (!D->isHidden() || isHiddenDeclarationVisible(D) ||
>>> >> -        isVisibleSlow(getSema(), D))
>>> >> +    if (isVisible(getSema(), D) || isHiddenDeclarationVisible(D))
>>> >>        return D;
>>> >>
>>> >>      return getAcceptableDeclSlow(D);
>>> >>
>>> >> Modified: cfe/trunk/test/Modules/submodule-visibility.cpp
>>> >> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Modules/submodule-visibility.cpp?rev=253012&r1=253011&r2=253012&view=diff
>>> >>
>>> ==============================================================================
>>> >> --- cfe/trunk/test/Modules/submodule-visibility.cpp (original)
>>> >> +++ cfe/trunk/test/Modules/submodule-visibility.cpp Thu Nov 12
>>> 23:14:45 2015
>>> >> @@ -28,3 +28,10 @@ int k = n + m; // OK, a and b are visibl
>>> >>  #ifndef B
>>> >>  #error B is not defined
>>> >>  #endif
>>> >> +
>>> >> +// Ensure we don't compute the linkage of this struct before we find
>>> it has a
>>> >> +// typedef name for linkage purposes.
>>> >> +typedef struct {
>>> >> +  int p;
>>> >> +  void (*f)(int p);
>>> >> +} name_for_linkage;
>>> >>
>>> >>
>>> >> _______________________________________________
>>> >> cfe-commits mailing list
>>> >> cfe-commits at lists.llvm.org
>>> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
>>> >
>>> >
>>>
>>
>>
>
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