hidden visibility with shared objects lead to subtle bugs

[serge-sans-paille]

Bugzilla Link	50237
Resolution	DUPLICATE
Resolved on	May 11, 2021 21:18
Version	trunk
OS	Linux
Blocks	#48661
CC	@bd1976bris,@pogo59,@tstellar

Extended Description

We should not set CMAKE_CXX_VISIBILITY_PRESET to hidden for llvm Targets

Using this feature is error prone and interacts in subtle ways with the LLVM
codebase.

As an example, 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.

See https://gcc.gnu.org/wiki/Visibility and https://gcc.gnu.org/onlinedocs/gcc/Vague-Linkage.html
for more information on that topic.

Proposed patch: https://reviews.llvm.org/D101972

[tstellar]

*** This bug has been marked as a duplicate of bug #48336 ***