[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