Author: smeenai Date: Mon Jul 24 10:16:27 2017 New Revision: 308899 URL: http://llvm.org/viewvc/llvm-project?rev=308899&view=rev Log: [CodeGen] Propagate dllexport to thunks
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. We need to export these thunks because they can be referenced outside the library they're defined in. For example, if a child class without a key function inherits from a parent class with a key function, the parent's thunks will only be defined in the library with the key function, but the construction vtable for the parent in the child might be emitted outside the library (since the child doesn't have a key function), and it needs to reference the parent's thunks. We don't need to mark these thunks as imported since any references to them will occur in data, so the compiler can't generate the IAT load sequence anyway. Instead, we rely on the linker generating import thunks for the thunks. Differential Revision: https://reviews.llvm.org/D34972 Added: cfe/trunk/test/CodeGenCXX/dllexport-vtable-thunks.cpp Modified: cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp Modified: cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp?rev=308899&r1=308898&r2=308899&view=diff ============================================================================== --- cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp (original) +++ cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp Mon Jul 24 10:16:27 2017 @@ -284,6 +284,14 @@ public: // linkage together with vtables when needed. if (ForVTable && !Thunk->hasLocalLinkage()) Thunk->setLinkage(llvm::GlobalValue::AvailableExternallyLinkage); + + // Propagate dllexport storage, to enable the linker to generate import + // thunks as necessary (e.g. when a parent class has a key function and a + // child class doesn't, and the construction vtable for the parent in the + // child needs to reference the parent's thunks). + const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl()); + if (MD->hasAttr<DLLExportAttr>()) + Thunk->setDLLStorageClass(llvm::GlobalValue::DLLExportStorageClass); } llvm::Value *performThisAdjustment(CodeGenFunction &CGF, Address This, Added: cfe/trunk/test/CodeGenCXX/dllexport-vtable-thunks.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/dllexport-vtable-thunks.cpp?rev=308899&view=auto ============================================================================== --- cfe/trunk/test/CodeGenCXX/dllexport-vtable-thunks.cpp (added) +++ cfe/trunk/test/CodeGenCXX/dllexport-vtable-thunks.cpp Mon Jul 24 10:16:27 2017 @@ -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 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
