[PATCH] D135919: [Clang] Set thread_local Itanium ABI guard variables before calling constructors.

[Tom Honermann via Phabricator via cfe-commits]

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Previously, for thread_local variables that do not require thread safe initialization, guard variables used in the Itanium ABI to store the initialization state of such a variable were set after object initialization was complete. This resulted in recursive re-initialization loops in cases where a constructor references the variable being initialized. For example:

  template<typename T>
  struct ct {
    ct();
  };
  template<typename T>
  ct<T>& ft() {
    static thread_local ct<T> tlslv;
    return tlslv;
  }
  template<typename T>
  ct<T>::ct() {
    ft<T>();
  }

With this change, guard variables are set before initialization is started so as to avoid such re-initialization loops. It is worth noting that, per C++20 [class.cdtor]p2, access to the value (as opposed to the address) of the object under construction via the thread_local variable results in unspecified behavior.

Fixes https://github.com/llvm/llvm-project/issues/57828


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D135919

Files:
  clang/lib/CodeGen/ItaniumCXXABI.cpp
  clang/test/CodeGenCXX/aix-static-init-temp-spec-and-inline-var.cpp
  clang/test/CodeGenCXX/cxx11-thread-local.cpp
  clang/test/CodeGenCXX/cxx1y-variable-template.cpp
  clang/test/CodeGenCXX/global-init.cpp
  clang/test/CodeGenCXX/static-data-member.cpp
  clang/test/OpenMP/parallel_copyin_codegen.cpp
  clang/test/OpenMP/threadprivate_codegen.cpp

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