[libc] add more APIs of cmgxchg variants

[SchrodingerZhu]

Such APIs are useful in lock implementations

[llvmbot]

@llvm/pr-subscribers-libc

Author: Schrodinger ZHU Yifan (SchrodingerZhu)

Changes

Such APIs are useful in lock implementations

---

Full diff: https://github.com/llvm/llvm-project/pull/91208.diff

1 Files Affected:

• (modified) libc/src/__support/CPP/atomic.h (+30)

diff --git a/libc/src/__support/CPP/atomic.h b/libc/src/__support/CPP/atomic.h
index 5e428940565b99..e273d998c07029 100644
--- a/libc/src/__support/CPP/atomic.h
+++ b/libc/src/__support/CPP/atomic.h
@@ -101,6 +101,36 @@ template <typename T> struct Atomic {
                                        int(mem_ord), int(mem_ord));
   }
 
+  // Atomic compare exchange (separate success and failure memory orders)
+  bool compare_exchange_strong(
+      T &expected, T desired, MemoryOrder success_order,
+      MemoryOrder failure_order,
+      [[maybe_unused]] MemoryScope mem_scope = MemoryScope::DEVICE) {
+    return __atomic_compare_exchange_n(&val, &expected, desired, false,
+                                       static_cast<int>(success_order),
+                                       static_cast<int>(failure_order));
+  }
+
+  // Atomic compare exchange (weak version)
+  bool compare_exchange_weak(
+      T &expected, T desired, MemoryOrder mem_ord = MemoryOrder::SEQ_CST,
+      [[maybe_unused]] MemoryScope mem_scope = MemoryScope::DEVICE) {
+    return __atomic_compare_exchange_n(&val, &expected, desired, true,
+                                       static_cast<int>(mem_ord),
+                                       static_cast<int>(mem_ord));
+  }
+
+  // Atomic compare exchange (weak version with separate success and failure
+  // memory orders)
+  bool compare_exchange_weak(
+      T &expected, T desired, MemoryOrder success_order,
+      MemoryOrder failure_order,
+      [[maybe_unused]] MemoryScope mem_scope = MemoryScope::DEVICE) {
+    return __atomic_compare_exchange_n(&val, &expected, desired, true,
+                                       static_cast<int>(success_order),
+                                       static_cast<int>(failure_order));
+  }
+
   T exchange(T desired, MemoryOrder mem_ord = MemoryOrder::SEQ_CST,
              [[maybe_unused]] MemoryScope mem_scope = MemoryScope::DEVICE) {
 #if __has_builtin(__scoped_atomic_exchange_n)