[libc++abi] Make once_flag constinit in cxa_exception_storage

[ldionne]

This makes it clearer that initialization of this global variable is taking place at compile-time, reducing the likelihood of static initialization order fiasco.

[llvmbot]

@llvm/pr-subscribers-libcxxabi

Author: Louis Dionne (ldionne)

Changes

This makes it clearer that initialization of this global variable is taking place at compile-time, reducing the likelihood of static initialization order fiasco.

---

Full diff: https://github.com/llvm/llvm-project/pull/124627.diff

1 Files Affected:

• (modified) libcxxabi/src/cxa_exception_storage.cpp (+1-1)

diff --git a/libcxxabi/src/cxa_exception_storage.cpp b/libcxxabi/src/cxa_exception_storage.cpp
index 733f0d470569a2..05da6a48e313cf 100644
--- a/libcxxabi/src/cxa_exception_storage.cpp
+++ b/libcxxabi/src/cxa_exception_storage.cpp
@@ -56,7 +56,7 @@ extern "C" {
 namespace __cxxabiv1 {
 namespace {
     std::__libcpp_tls_key key_;
-    std::__libcpp_exec_once_flag flag_ = _LIBCPP_EXEC_ONCE_INITIALIZER;
+    constinit std::__libcpp_exec_once_flag flag_ = _LIBCPP_EXEC_ONCE_INITIALIZER;
 
     void _LIBCPP_TLS_DESTRUCTOR_CC destruct_(void *p) {
         __free_with_fallback(p);