[lld] lld::makeThreadLocal: omit thread_local when threads disabled

[keithw]

This PR lets lld be used as a library in single-threaded environments without TLS.

[llvmbot]

@llvm/pr-subscribers-lld

Author: Keith Winstein (keithw)

Changes

This PR lets lld be used as a library in single-threaded environments without TLS.

---

Full diff: https://github.com/llvm/llvm-project/pull/72057.diff

1 Files Affected:

• (modified) lld/include/lld/Common/Memory.h (+4)

diff --git a/lld/include/lld/Common/Memory.h b/lld/include/lld/Common/Memory.h
index c7612a08c6b00db..23e8737bcc207be 100644
--- a/lld/include/lld/Common/Memory.h
+++ b/lld/include/lld/Common/Memory.h
@@ -65,7 +65,11 @@ template <typename T, typename... U> T *make(U &&... args) {
 template <typename T>
 inline llvm::SpecificBumpPtrAllocator<T> &
 getSpecificAllocSingletonThreadLocal() {
+  #if LLVM_ENABLE_THREADS
   thread_local SpecificAlloc<T> instance;
+  #else
+  static SpecificAlloc<T> instance;
+  #endif
   return instance.alloc;
 }
 

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[keithw]

@smithp35 @MaskRay

[MaskRay]

Can you describe how is your single-threaded environment look like? Is thread_local an error for your compiler, linker, or loader?

It seems that we don't use thread_local for !LLVM_ENABLE_THREADS configurations in llvm/ and clang/ (but not mlir/) and I don't think it is good for the project if we add a lot of code in non-testable configurations (those with very special requirements).

---

static LLVM_THREAD_LOCAL should look better.

[MaskRay]

.