diff --git a/compiler-rt/lib/builtins/atomic.c b/compiler-rt/lib/builtins/atomic.c
--- a/compiler-rt/lib/builtins/atomic.c
+++ b/compiler-rt/lib/builtins/atomic.c
@@ -36,6 +36,8 @@
 #pragma redefine_extname __atomic_exchange_c SYMBOL_NAME(__atomic_exchange)
 #pragma redefine_extname __atomic_compare_exchange_c SYMBOL_NAME(              \
     __atomic_compare_exchange)
+#pragma redefine_extname __atomic_is_lock_free_c SYMBOL_NAME(                  \
+    __atomic_is_lock_free)
 
 /// Number of locks.  This allocates one page on 32-bit platforms, two on
 /// 64-bit.  This can be specified externally if a different trade between
@@ -157,6 +159,14 @@
     }                                                                          \
   } while (0)
 
+/// Whether atomic operations for the given size (and alignment) are lock-free.
+bool __atomic_is_lock_free_c(size_t size, void *ptr) {
+#define LOCK_FREE_ACTION(type) return true;
+  LOCK_FREE_CASES(ptr);
+#undef LOCK_FREE_ACTION
+  return false;
+}
+
 /// An atomic load operation.  This is atomic with respect to the source
 /// pointer only.
 void __atomic_load_c(int size, void *src, void *dest, int model) {