[OMPT] Make sure that OMPT is enabled when accessing internals of the runtime

The three switch fallthrough generate a warning with -Wimplicit-fallthrough.
Two are documented as fallthrough, one is not, but I think the intention is to also fallthrough in kmp_tasking.cpp.

Not sure whether kmp.h is the best place to define the macro.

Reviewers: jlpeyton, AndreyChurbanov, Hahnfeld

Reviewed By: jlpeyton

Tags: #openmp

Differential Revision: https://reviews.llvm.org/D56397

llvm-svn: 353052

openmp/runtime/src/kmp_dispatch.cpp

@@ -348,6 +348,7 @@ void __kmp_dispatch_init_algorithm(ident_t *loc, int gtid,
       /* too few iterations: fall-through to kmp_sch_static_balanced */
     } // if
     /* FALL-THROUGH to static balanced */
+    KMP_FALLTHROUGH();
   } // case
 #endif
   case kmp_sch_static_balanced: {

openmp/runtime/src/kmp_os.h

@@ -296,6 +296,20 @@ extern "C" {
 
 #define KMP_CACHE_PREFETCH(ADDR) /* nothing */
 
+// Define attribute that indicates that the fall through from the previous 
+// case label is intentional and should not be diagnosed by a compiler
+//   Code 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 KMP_FALLTHROUGH() [[fallthrough]]
+#elif __has_cpp_attribute(clang::fallthrough)
+#  define KMP_FALLTHROUGH() [[clang::fallthrough]]
+#elif __has_attribute(fallthough) || _GNUC_VER >= 700
+#  define KMP_FALLTHROUGH() __attribute__((__fallthrough__))
+#else
+#  define KMP_FALLTHROUGH() ((void)0)
+#endif
+
 // Define attribute that indicates a function does not return
 #if __cplusplus >= 201103L
 #define KMP_NORETURN [[noreturn]]

openmp/runtime/src/kmp_runtime.cpp

@@ -6421,6 +6421,7 @@ void __kmp_register_library_startup(void) {
         // library. Assume the other library is alive.
         // WARN( ... ); // TODO: Issue a warning.
         file_name = "unknown library";
+        KMP_FALLTHROUGH();
       // Attention! Falling to the next case. That's intentional.
       case 1: { // Neighbor is alive.
         // Check it is allowed.

openmp/runtime/src/kmp_tasking.cpp

@@ -4205,6 +4205,7 @@ void __kmpc_taskloop(ident_t *loc, int gtid, kmp_task_t *task, int if_val,
   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;
+    KMP_FALLTHROUGH();
   case 2: // num_tasks provided
     if (grainsize > tc) {
       num_tasks = tc; // too big num_tasks requested, adjust values