[llvm-branch-commits] [clang] release/19.x: [clang] Define `ATOMIC_FLAG_INIT` correctly for C++. (#97534) (PR #100365)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: None (llvmbot)

<details>
<summary>Changes</summary>

Backport 4bb3a1e16f3a854d05bc0b8c5b6f8f78effb1d93

Requested by: @<!-- -->AaronBallman

---
Full diff: https://github.com/llvm/llvm-project/pull/100365.diff


3 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+3) 
- (modified) clang/lib/Headers/stdatomic.h (+4) 
- (modified) clang/test/Headers/stdatomic.c (+5) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 24d88ed6edf00..5b6ee9830b507 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -891,6 +891,9 @@ Bug Fixes in This Version
 - Fixed an assertion failure when a template non-type parameter contains
   an invalid expression.
 
+- Fixed the definition of ``ATOMIC_FLAG_INIT`` in ``<stdatomic.h>`` so it can
+  be used in C++.
+
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/clang/lib/Headers/stdatomic.h b/clang/lib/Headers/stdatomic.h
index 2027055f38796..1991351f9e9ef 100644
--- a/clang/lib/Headers/stdatomic.h
+++ b/clang/lib/Headers/stdatomic.h
@@ -172,7 +172,11 @@ typedef _Atomic(uintmax_t)          atomic_uintmax_t;
 
 typedef struct atomic_flag { atomic_bool _Value; } atomic_flag;
 
+#ifdef __cplusplus
+#define ATOMIC_FLAG_INIT {false}
+#else
 #define ATOMIC_FLAG_INIT { 0 }
+#endif
 
 /* These should be provided by the libc implementation. */
 #ifdef __cplusplus
diff --git a/clang/test/Headers/stdatomic.c b/clang/test/Headers/stdatomic.c
index 3643fd4245b31..9afd531a9ed9b 100644
--- a/clang/test/Headers/stdatomic.c
+++ b/clang/test/Headers/stdatomic.c
@@ -1,5 +1,8 @@
 // RUN: %clang_cc1 -std=c11 -E %s | FileCheck %s
 // RUN: %clang_cc1 -std=c11 -fms-compatibility -E %s | FileCheck %s
+// RUN: %clang_cc1 -std=c11 %s -verify
+// RUN: %clang_cc1 -x c++ -std=c++11 %s -verify
+// expected-no-diagnostics
 #include <stdatomic.h>
 
 int bool_lock_free = ATOMIC_BOOL_LOCK_FREE;
@@ -31,3 +34,5 @@ int llong_lock_free = ATOMIC_LLONG_LOCK_FREE;
 
 int pointer_lock_free = ATOMIC_POINTER_LOCK_FREE;
 // CHECK: pointer_lock_free = {{ *[012] *;}}
+
+atomic_flag f = ATOMIC_FLAG_INIT;

``````````

</details>


https://github.com/llvm/llvm-project/pull/100365