[OpenMP] Introduce GOMP taskwait depend in the runtime

This change introduces the GOMP_taskwait_depend() function. It implements
the OpenMP 5.0 feature of #pragma omp taskwait with depend() clause by
wrapping around __kmpc_omp_wait_deps().

Differential Revision: https://reviews.llvm.org/D87269

Author: Peyton, Jonathan L

openmp/runtime/src/kmp_ftn_os.h

@@ -680,5 +680,6 @@
 #define KMP_API_NAME_GOMP_PARALLEL_LOOP_MAYBE_NONMONOTONIC_RUNTIME             \
   GOMP_parallel_loop_maybe_nonmonotonic_runtime
 #define KMP_API_NAME_GOMP_TEAMS_REG GOMP_teams_reg
+#define KMP_API_NAME_GOMP_TASKWAIT_DEPEND GOMP_taskwait_depend
 
 #endif /* KMP_FTN_OS_H */

openmp/runtime/src/kmp_gsupport.cpp

@@ -1867,6 +1867,19 @@ void KMP_EXPAND_NAME(KMP_API_NAME_GOMP_TEAMS_REG)(void (*fn)(void *),
   KA_TRACE(20, ("GOMP_teams_reg exit: T#%d\n", gtid));
 }
 
+void KMP_EXPAND_NAME(KMP_API_NAME_GOMP_TASKWAIT_DEPEND)(void **depend) {
+  MKLOC(loc, "GOMP_taskwait_depend");
+  int gtid = __kmp_entry_gtid();
+  KA_TRACE(20, ("GOMP_taskwait_depend: T#%d\n", gtid));
+  kmp_gomp_depends_info_t gomp_depends(depend);
+  kmp_int32 ndeps = gomp_depends.get_num_deps();
+  kmp_depend_info_t dep_list[ndeps];
+  for (kmp_int32 i = 0; i < ndeps; i++)
+    dep_list[i] = gomp_depends.get_kmp_depend(i);
+  __kmpc_omp_wait_deps(&loc, gtid, ndeps, dep_list, 0, NULL);
+  KA_TRACE(20, ("GOMP_taskwait_depend exit: T#%d\n", gtid));
+}
+
 /* The following sections of code create aliases for the GOMP_* functions, then
    create versioned symbols using the assembler directive .symver. This is only
    pertinent for ELF .so library. The KMP_VERSION_SYMBOL macro is defined in
@@ -2039,6 +2052,7 @@ KMP_VERSION_SYMBOL(KMP_API_NAME_GOMP_PARALLEL_LOOP_NONMONOTONIC_RUNTIME, 50,
 KMP_VERSION_SYMBOL(KMP_API_NAME_GOMP_PARALLEL_LOOP_MAYBE_NONMONOTONIC_RUNTIME,
                    50, "GOMP_5.0");
 KMP_VERSION_SYMBOL(KMP_API_NAME_GOMP_TEAMS_REG, 50, "GOMP_5.0");
+KMP_VERSION_SYMBOL(KMP_API_NAME_GOMP_TASKWAIT_DEPEND, 50, "GOMP_5.0");
 
 #endif // KMP_USE_VERSION_SYMBOLS
 

openmp/runtime/test/tasking/omp50_taskwait_depend.c

@@ -0,0 +1,108 @@
+// RUN: %libomp-compile-and-run
+// UNSUPPORTED: gcc-4, gcc-5, gcc-6, gcc-7, gcc-8
+// clang does not yet support taskwait with depend clause
+// clang-12 introduced parsing, but no codegen
+// TODO: update expected result when codegen in clang is added
+// icc does not yet support taskwait with depend clause
+// TODO: update expected result when support for icc is added
+// XFAIL: clang, icc
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <omp.h>
+#include "omp_my_sleep.h"
+
+int a = 0, b = 0;
+int task_grabbed = 0, task_can_proceed = 0;
+int task2_grabbed = 0, task2_can_proceed = 0;
+
+static void wait_on_flag(int *flag) {
+  int flag_value;
+  int timelimit = 30;
+  int secs = 0;
+  do {
+    #pragma omp atomic read
+    flag_value = *flag;
+    my_sleep(1.0);
+    secs++;
+    if (secs == timelimit) {
+      fprintf(stderr, "error: timeout in wait_on_flag()\n");
+      exit(EXIT_FAILURE);
+    }
+  } while (flag_value == 0);
+}
+
+static void signal_flag(int *flag) {
+  #pragma omp atomic
+  (*flag)++;
+}
+
+int main(int argc, char** argv) {
+
+  // Ensure two threads are running
+  int num_threads = omp_get_max_threads();
+  if (num_threads < 2)
+    omp_set_num_threads(2);
+
+  #pragma omp parallel shared(a)
+  {
+    int a_value;
+    // Let us be extra safe here
+    if (omp_get_num_threads() > 1) {
+      #pragma omp single nowait
+      {
+        // Schedule independent child task that
+        // waits to be flagged after sebsequent taskwait depend()
+        #pragma omp task
+        {
+          signal_flag(&task_grabbed);
+          wait_on_flag(&task_can_proceed);
+        }
+        // Let another worker thread grab the task to execute
+        wait_on_flag(&task_grabbed);
+        // This should be ignored since the task above has
+        // no dependency information
+        #pragma omp taskwait depend(inout: a)
+        // Signal the independent task to proceed
+        signal_flag(&task_can_proceed);
+
+        // Schedule child task with dependencies that taskwait does
+        // not care about
+        #pragma omp task depend(inout: b)
+        {
+          signal_flag(&task2_grabbed);
+          wait_on_flag(&task2_can_proceed);
+          #pragma omp atomic
+          b++;
+        }
+        // Let another worker thread grab the task to execute
+        wait_on_flag(&task2_grabbed);
+        // This should be ignored since the task above has
+        // dependency information on b instead of a
+        #pragma omp taskwait depend(inout: a)
+        // Signal the task to proceed
+        signal_flag(&task2_can_proceed);
+
+        // Generate one child task for taskwait
+        #pragma omp task shared(a) depend(inout: a)
+        {
+          my_sleep(1.0);
+          #pragma omp atomic
+          a++;
+        }
+        #pragma omp taskwait depend(inout: a)
+
+        #pragma omp atomic read
+        a_value = a;
+
+        if (a_value != 1) {
+          fprintf(stderr, "error: dependent task was not executed before "
+                          "taskwait finished\n");
+          exit(EXIT_FAILURE);
+        }
+      } // #pragma omp single
+    } // if (num_threads > 1)
+  } // #pragma omp parallel
+
+  return EXIT_SUCCESS;
+}