If the thinks are not imported, why would it make sense to export them? Maybe devirtualization could trigger this?
On Wed, Jul 5, 2017 at 1:17 PM Shoaib Meenai <smee...@fb.com> wrote: > The thunks are (as far as I know, at least) only referenced from vtables, > so > there's no opportunity to perform indirect calls via the IAT for them. The > vtable would just end up referencing the linker-generated import thunk > instead. > > I can play around with marking the thunks as dllimport if the function > being > thunked is dllimport, but I was curious if you had any specific scenarios > in > mind where you thought it would make a difference. > > From: cfe-commits <cfe-commits-boun...@lists.llvm.org> on behalf of David > Majnemer via cfe-commits <cfe-commits@lists.llvm.org> > Reply-To: David Majnemer <david.majne...@gmail.com> > Date: Tuesday, July 4, 2017 at 8:42 AM > To: Shoaib Meenai via Phabricator <revi...@reviews.llvm.org>, " > compn...@compnerd.org" <compn...@compnerd.org>, " > reviews+d34972+public+8a22767368a5b...@reviews.llvm.org" < > reviews+d34972+public+8a22767368a5b...@reviews.llvm.org>, "r...@google.com" > <r...@google.com> > Cc: "ztur...@google.com" <ztur...@google.com>, "cfe-commits@lists.llvm.org" > <cfe-commits@lists.llvm.org> > Subject: Re: [PATCH] D34972: [CodeGen] Propagate dllexport to thunks > > What about the import side? > > On Mon, Jul 3, 2017 at 10:37 PM Shoaib Meenai via Phabricator via > cfe-commits <cfe-commits@lists.llvm.org> wrote: > smeenai created this revision. > > Under Windows Itanium, we need to export virtual and non-virtual thunks > if the functions being thunked are exported. These thunks would > previously inherit their dllexport attribute from the declaration, but > r298330 changed declarations to not have dllexport attributes. We > therefore need to add the dllexport attribute to the definition > ourselves now. This is consistent with MinGW GCC's behavior. > > This redoes r306770 but limits the logic to Itanium. MicrosoftCXXABI's > setThunkLinkage ensures that thunks aren't exported under that ABI, so > I'm handling this in ItaniumCXXABI's setThunkLinkage for symmetry. > > > https://reviews.llvm.org/D34972 > > Files: > lib/CodeGen/ItaniumCXXABI.cpp > test/CodeGenCXX/dllexport-vtable-thunks.cpp > > > Index: test/CodeGenCXX/dllexport-vtable-thunks.cpp > =================================================================== > --- /dev/null > +++ test/CodeGenCXX/dllexport-vtable-thunks.cpp > @@ -0,0 +1,23 @@ > +// RUN: %clang_cc1 -triple x86_64-windows-gnu -fdeclspec -emit-llvm -o - > %s | FileCheck %s > +// RUN: %clang_cc1 -triple x86_64-windows-itanium -fdeclspec -emit-llvm > -o - %s | FileCheck %s > + > +struct __declspec(dllexport) A { > + virtual void m(); > +}; > +struct __declspec(dllexport) B { > + virtual void m(); > +}; > +struct __declspec(dllexport) C : A, B { > + virtual void m(); > +}; > +void C::m() {} > +// CHECK: define dllexport void @_ZThn8_N1C1mEv > + > +struct Base { > + virtual void m(); > +}; > +struct __declspec(dllexport) Derived : virtual Base { > + virtual void m(); > +}; > +void Derived::m() {} > +// CHECK: define dllexport void @_ZTv0_n24_N7Derived1mEv > Index: lib/CodeGen/ItaniumCXXABI.cpp > =================================================================== > --- lib/CodeGen/ItaniumCXXABI.cpp > +++ lib/CodeGen/ItaniumCXXABI.cpp > @@ -284,6 +284,11 @@ > // linkage together with vtables when needed. > if (ForVTable && !Thunk->hasLocalLinkage()) > Thunk->setLinkage(llvm::GlobalValue::AvailableExternallyLinkage); > + > + // Propagate dllexport storage. > + const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl()); > + if (MD->hasAttr<DLLExportAttr>()) > + Thunk->setDLLStorageClass(llvm::GlobalValue::DLLExportStorageClass); > } > > llvm::Value *performThisAdjustment(CodeGenFunction &CGF, Address This, > > > _______________________________________________ > cfe-commits mailing list > cfe-commits@lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits > > >
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