Index: runtime/src/kmp.h
===================================================================
--- runtime/src/kmp.h
+++ runtime/src/kmp.h
@@ -3970,6 +3970,18 @@
 extern int __kmpc_get_target_offload();
 #endif
 
+// from libcxx/include/__config
+// Use a function like macro to imply that it must be followed by a semicolon
+#if __cplusplus > 201402L && __has_cpp_attribute(fallthrough)
+#  define _LIBOMP_FALLTHROUGH() [[fallthrough]]
+#elif __has_cpp_attribute(clang::fallthrough)
+#  define _LIBOMP_FALLTHROUGH() [[clang::fallthrough]]
+#elif __has_attribute(fallthough) || _GNUC_VER >= 700
+#  define _LIBOMP_FALLTHROUGH() __attribute__((__fallthrough__))
+#else
+#  define _LIBOMP_FALLTHROUGH() ((void)0)
+#endif
+
 #ifdef __cplusplus
 }
 #endif
Index: runtime/src/kmp_dispatch.cpp
===================================================================
--- runtime/src/kmp_dispatch.cpp
+++ runtime/src/kmp_dispatch.cpp
@@ -349,6 +349,7 @@
       /* too few iterations: fall-through to kmp_sch_static_balanced */
     } // if
     /* FALL-THROUGH to static balanced */
+    _LIBOMP_FALLTHROUGH();
   } // case
 #endif
   case kmp_sch_static_balanced: {
Index: runtime/src/kmp_runtime.cpp
===================================================================
--- runtime/src/kmp_runtime.cpp
+++ runtime/src/kmp_runtime.cpp
@@ -6343,6 +6343,7 @@
         // library. Assume the other library is alive.
         // WARN( ... ); // TODO: Issue a warning.
         file_name = "unknown library";
+        _LIBOMP_FALLTHROUGH();
       // Attention! Falling to the next case. That's intentional.
       case 1: { // Neighbor is alive.
         // Check it is allowed.
Index: runtime/src/kmp_tasking.cpp
===================================================================
--- runtime/src/kmp_tasking.cpp
+++ runtime/src/kmp_tasking.cpp
@@ -4204,6 +4204,7 @@
   case 0: // no schedule clause specified, we can choose the default
     // let's try to schedule (team_size*10) tasks
     grainsize = thread->th.th_team_nproc * 10;
+    _LIBOMP_FALLTHROUGH();
   case 2: // num_tasks provided
     if (grainsize > tc) {
       num_tasks = tc; // too big num_tasks requested, adjust values