[PATCH] D51340: Add /Zc:DllexportInlines option to clang-cl

[Takuto Ikuta via Phabricator via cfe-commits]

takuto.ikuta added inline comments.


================
Comment at: clang/lib/Sema/SemaDecl.cpp:11976
+
+    while (FD && !getDLLAttr(FD) &&
+           !FD->hasAttr<DLLExportStaticLocalAttr>() &&
----------------
hans wrote:
> takuto.ikuta wrote:
> > hans wrote:
> > > Why does this need to be a loop? I don't think FunctionDecl's can be nested?
> > This is for static local var in lambda function.
> > static_x's ParentFunction does not become f().
> > ```
> > class __declspec(dllexport) C {
> >   int f() {
> >     return ([]() { static int static_x; return ++static_x; })();
> >   }
> > };
> > ```
> I don't think the lambda (or its static local) should be exported in this case.
If we don't export static_x, dllimport library cannot find static_x when linking?




================
Comment at: clang/lib/Sema/SemaDecl.cpp:11995
+
+        // Function having static local variables should be exported.
+        auto *ExportAttr = cast<InheritableAttr>(NewAttr->clone(getASTContext()));
----------------
hans wrote:
> takuto.ikuta wrote:
> > hans wrote:
> > > Isn't it enough that the static local is exported, does the function itself need to be exported too?
> > Adding dllexport only to variable does not export variable when the function is not used.
> > But dllimport is not necessary for function, removed.
> Hmm, I wonder if we could fix that instead? That is, export the variable in that case even if the function is not used?
I see. I'll investigate which code path emits static variables


================
Comment at: clang/lib/Sema/SemaDeclCXX.cpp:5719
+          TSK != TSK_ExplicitInstantiationDeclaration &&
+          TSK != TSK_ExplicitInstantiationDefinition) {
+        if (ClassExported) {
----------------
hans wrote:
> I still don't understand why we need these checks for template instantiations. Why does it matter whether the functions get inlined or not?
When function of dllimported class is not inlined, such funtion needs to be dllexported from implementation library.

c.h
```
template<typename T>
class EXPORT C {
 public:
  void f() {}
};
```

cuser.cc
```
#include "c.h"

void cuser() {
  C<int> c;
  c.f();  // This function may not be inlined when EXPORT is __declspec(dllimport), so link may fail.
}
```

When cuser.cc and c.h are built to different library, cuser.cc needs to be able to see dllexported C::f() when C::f() is not inlined.
This is my understanding.


https://reviews.llvm.org/D51340