[COFF] Don't try to emit weak aliases on COFF
This comes up when a derived class destructor is equivalent to a base
class destructor defined in the same TU, and we try to alias them.
A COFF weak alias cannot satisfy a normal undefined symbol reference
from another TU. The other TU must also mark the referenced symbol as
weak, and we can't rely on that.
Clang already has a special case here for dllexport, but we failed to
realize that the problem also applies to other non-discardable symbols
such as those from explicit template instantiations.
Fixes PR25477.
llvm-svn: 252659
diff --git a/clang/lib/CodeGen/CGCXX.cpp b/clang/lib/CodeGen/CGCXX.cpp
index ea32e38..6847df9 100644
--- a/clang/lib/CodeGen/CGCXX.cpp
+++ b/clang/lib/CodeGen/CGCXX.cpp
@@ -131,11 +131,6 @@
if (!llvm::GlobalAlias::isValidLinkage(Linkage))
return true;
- // Don't create a weak alias for a dllexport'd symbol.
- if (AliasDecl.getDecl()->hasAttr<DLLExportAttr>() &&
- llvm::GlobalValue::isWeakForLinker(Linkage))
- return true;
-
llvm::GlobalValue::LinkageTypes TargetLinkage =
getFunctionLinkage(TargetDecl);
@@ -173,6 +168,16 @@
return false;
}
+ // If we have a weak, non-discardable alias (weak, weak_odr), like an extern
+ // template instantiation or a dllexported class, avoid forming it on COFF.
+ // A COFF weak external alias cannot satisfy a normal undefined symbol
+ // reference from another TU. The other TU must also mark the referenced
+ // symbol as weak, which we cannot rely on.
+ if (llvm::GlobalValue::isWeakForLinker(Linkage) &&
+ getTriple().isOSBinFormatCOFF()) {
+ return true;
+ }
+
if (!InEveryTU) {
// If we don't have a definition for the destructor yet, don't
// emit. We can't emit aliases to declarations; that's just not
diff --git a/clang/test/CodeGenCXX/microsoft-abi-structors-alias.cpp b/clang/test/CodeGenCXX/microsoft-abi-structors-alias.cpp
index 6007e5a..08df374 100644
--- a/clang/test/CodeGenCXX/microsoft-abi-structors-alias.cpp
+++ b/clang/test/CodeGenCXX/microsoft-abi-structors-alias.cpp
@@ -24,3 +24,19 @@
}
// CHECK-DAG: @"\01??1B@test2@@UAE@XZ" = alias void (%"struct.test2::B"*), bitcast (void (%"struct.test2::A"*)* @"\01??1A@test2@@UAE@XZ" to void (%"struct.test2::B"*)*)
}
+
+namespace test3 {
+struct A { virtual ~A(); };
+A::~A() {}
+}
+// CHECK-DAG: define x86_thiscallcc void @"\01??1A@test3@@UAE@XZ"(
+namespace test3 {
+template <typename T>
+struct B : A {
+ virtual ~B() { }
+};
+template struct B<int>;
+}
+// This has to be weak, and emitting weak aliases is fragile, so we don't do the
+// aliasing.
+// CHECK-DAG: define weak_odr x86_thiscallcc void @"\01??1?$B@H@test3@@UAE@XZ"(