Extended Description

When an odr-use of a constinit thread_local variable of incomplete class type occurs, Clang does not make any attempt to register the odr-use (and thus the initialization and any associated destructor calls). The case where the variable is a (possibly multi-dimensional) array of an incomplete class type is similarly affected.

SOURCE ():

struct A;
extern constinit thread_local A a;
A &foo() { return a; }

COMPILER INVOCATION:

clang -cc1 -emit-llvm -Wall -Wextra -Werror -pedantic-errors -std=c++20 -xc++ -std=c++20 -

ACTUAL OUTPUT (IR snippet):

define dso_local nonnull align 1 %struct.A* @​_Z3foov() #​0 {
entry:
ret %struct.A* @​a
}

EXPECTED OUTPUT (IR snippet):

define dso_local nonnull align 1 dereferenceable(1) %struct.A* @​_Z3foov() #​0 {
entry:
%0 = call %struct.A* @​_ZTW1a()
ret %struct.A* %0
}

COMPILER VERSION INFO (clang++ -v):

clang version 13.0.0 (https://github.com/llvm/llvm-project.git c4ed142)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/wandbox/clang-head/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.5.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@MX32
Selected multilib: .;@m64