takuto.ikuta added inline comments.
================
Comment at: clang/lib/AST/ASTContext.cpp:9552
+ // overwrite linkage of explicit template instantiation
+ // definition/declaration.
+ return GVA_DiscardableODR;
----------------
hans wrote:
> takuto.ikuta wrote:
> > takuto.ikuta wrote:
> > > hans wrote:
> > > > Can you give an example for why this is needed?
> > > Sorry, this change does not need. Removed.
> > Sorry, this change is necessary still.
> >
> > Without this, definition of inline function in explicit template
> > instantiation declaration is not be emitted, due to GVA_AvailableExternally
> > linkage.
> > But we stop exporting definition of inline function in explicit template
> > instantiation definition too.
> >
> > So without this, definition of dllimported inline function of explicit
> > template instantiation declaration won't be available.
> >
> Can you provide a code example of why this is needed?
If we don't change function linkage, following code will be compiled like below
with -fno-dllexport-inlines.
```
template<typename>
class M{
public:
void foo() {}
};
template class __declspec(dllexport) M<int>;
extern template class __declspec(dllimport) M<short>;
void f (){
M<int> mi;
mi.foo();
M<short> ms;
ms.foo();
}
```
```
$"?foo@?$M@H@@QEAAXXZ" = comdat any
; Function Attrs: noinline nounwind optnone
define weak_odr dso_local void @"?foo@?$M@H@@QEAAXXZ"(%class.M* %this) #0
comdat align 2 {
entry:
%this.addr = alloca %class.M*, align 8
store %class.M* %this, %class.M** %this.addr, align 8
%this1 = load %class.M*, %class.M** %this.addr, align 8
ret void
}
; Function Attrs: noinline nounwind optnone
define dso_local void @"?f@@YAXXZ"() #0 {
entry:
%mi = alloca %class.M, align 1
%ms = alloca %class.M.0, align 1
call void @"?foo@?$M@H@@QEAAXXZ"(%class.M* %mi)
call void @"?foo@?$M@F@@QEAAXXZ"(%class.M.0* %ms)
ret void
}
declare dso_local void @"?foo@?$M@F@@QEAAXXZ"(%class.M.0*) #1
```
M<short>::foo() is declared, but inline function is not dllexported (See
M<int>::foo() is not dllexported). So this code cannot be linked because
definition of M<short>::foo does not exist. If the function is properly
inlined, we don't need to have this code. But I'm not sure why the function is
not inlined.
https://reviews.llvm.org/D51340
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