diff --git a/clang/lib/Headers/__clang_cuda_device_functions.h b/clang/lib/Headers/__clang_cuda_device_functions.h
--- a/clang/lib/Headers/__clang_cuda_device_functions.h
+++ b/clang/lib/Headers/__clang_cuda_device_functions.h
@@ -519,6 +519,7 @@
   return __nv_fast_sincosf(__a, __s, __c);
 }
 __DEVICE__ float __sinf(float __a) { return __nv_fast_sinf(__a); }
+__DEVICE__ int __syncthreads() { return __nvvm_bar(); }
 __DEVICE__ int __syncthreads_and(int __a) { return __nvvm_bar0_and(__a); }
 __DEVICE__ int __syncthreads_count(int __a) { return __nvvm_bar0_popc(__a); }
 __DEVICE__ int __syncthreads_or(int __a) { return __nvvm_bar0_or(__a); }