Force visibility of llvm::Any to external
llvm::Any::TypeId::Id relies on the uniqueness of the address of a static
variable defined in a template function. hidden visibility implies vague linkage
for that variable, which does not guarantee the uniqueness of the address across
a binary and a shared library. This totally breaks the implementation of
llvm::Any.
Ideally, setting visibility to llvm::Any::TypeId::Id should be enough,
unfortunately this doesn't work as expected and we lack time (before 12.0.1
release) to understand why setting the visibility to llvm::Any does work.
See https://gcc.gnu.org/wiki/Visibility and
https://gcc.gnu.org/onlinedocs/gcc/Vague-Linkage.html
for more information on that topic.
Differential Revision: https://reviews.llvm.org/D101972
(cherry picked from commit 3d3abc22b3ef189813a3b9061c2a90ba86a32f44)
diff --git a/llvm/include/llvm/ADT/Any.h b/llvm/include/llvm/ADT/Any.h
index 0aded62..1e3abca 100644
--- a/llvm/include/llvm/ADT/Any.h
+++ b/llvm/include/llvm/ADT/Any.h
@@ -23,7 +23,12 @@
namespace llvm {
-class Any {
+class LLVM_EXTERNAL_VISIBILITY Any {
+
+ // The `Typeid<T>::Id` static data member below is a globally unique
+ // identifier for the type `T`. It is explicitly marked with default
+ // visibility so that when `-fvisibility=hidden` is used, the loader still
+ // merges duplicate definitions across DSO boundaries.
template <typename T> struct TypeId { static const char Id; };
struct StorageBase {
