[all-commits] [llvm/llvm-project] 072e2a: [MS] Implement on-demand TLS initialization for Mi...

[Maurice Heumann via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 072e2a7c67b74b8bde35f78ac0b0b13a269380f8
      https://github.com/llvm/llvm-project/commit/072e2a7c67b74b8bde35f78ac0b0b13a269380f8
  Author: Maurice Heumann <MauriceHeumann at gmail.com>
  Date:   2022-01-13 (Thu, 13 Jan 2022)

  Changed paths:
    M clang/include/clang/Basic/LangOptions.h
    M clang/lib/CodeGen/CGCXXABI.cpp
    M clang/lib/CodeGen/CGCXXABI.h
    M clang/lib/CodeGen/ItaniumCXXABI.cpp
    M clang/lib/CodeGen/MicrosoftCXXABI.cpp
    M clang/test/CodeGenCXX/ms-thread_local.cpp

  Log Message:
  -----------
  [MS] Implement on-demand TLS initialization for Microsoft CXX ABI

TLS initializers, for example constructors of thread-local variables, don't necessarily get called. If a thread was created before a module is loaded, the module's TLS initializers are not executed for this particular thread.

This is why Microsoft added support for dynamic TLS initialization. Before every use of thread-local variables, a check is added that runs the module's TLS initializers on-demand.

To do this, the method `__dyn_tls_on_demand_init` gets called. Internally, it simply calls `__dyn_tls_init`.

No additional TLS initializer that sets the guard needs to be emitted, as the guard always gets set by `__dyn_tls_init`.
The guard is also checked again within `__dyn_tls_init`. This makes our check redundant, however, as Microsoft's compiler also emits this check, the behaviour is adopted here.

Reviewed By: majnemer

Differential Revision: https://reviews.llvm.org/D115456