Avoid producing mismatched comdats.

The problem was that given

template<typename T>
struct foo {
  ~foo() {}
};
template class foo<int>;

We would produce a alias, creating a comdat with D0 and D1, since the symbols
have to be weak. Another TU is not required to have a explicit template
instantiation definition or an explict template instantiation declaration and
for

template<typename T>
struct foo {
  ~foo() {}
};
foo<int> a;

we would produce a comdat with only one symbol in it.

llvm-svn: 194520

1 files changed, 7 insertions, 6 deletions

diff --git a/clang/lib/CodeGen/CGCXX.cpp b/clang/lib/CodeGen/CGCXX.cpp
index 0f55616ea6b..b16c59d5f65 100644
--- a/clang/lib/CodeGen/CGCXX.cpp
+++ b/clang/lib/CodeGen/CGCXX.cpp
@@ -146,14 +146,15 @@ bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
     /// how aliases work.
     if (Ref->isDeclaration())
       return true;
-
-    // Don't create an alias to a linker weak symbol unless we know we can do
-    // that in every TU. This avoids producing different COMDATs in different
-    // TUs.
-    if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
-      return true;
   }
 
+  // Don't create an alias to a linker weak symbol. This avoids producing
+  // different COMDATs in different TUs. Another option would be to
+  // output the alias both for weak_odr and linkonce_odr, but that
+  // requires explicit comdat support in the IL.
+  if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
+    return true;
+
   // Create the alias with no name.
   llvm::GlobalAlias *Alias = 
     new llvm::GlobalAlias(AliasType, Linkage, "", Aliasee, &getModule());