openmp: Add taskwait nowait depend support [PR105378]

This patch adds support for (so far C/C++)
  #pragma omp taskwait nowait depend(...)
directive, which is like
  #pragma omp task depend(...)
  ;
but slightly optimized on the library side, so that it creates
the task only for the purpose of dependency tracking and doesn't actually
schedule it and wait for it when the dependencies are satisfied, instead
makes its dependencies satisfied right away.

2022-05-24  Jakub Jelinek  <jakub@redhat.com>

	PR c/105378
gcc/
	* omp-builtins.def (BUILT_IN_GOMP_TASKWAIT_DEPEND_NOWAIT): New
	builtin.
	* gimplify.cc (gimplify_omp_task): Diagnose taskwait with nowait
	clause but no depend clauses.
	* omp-expand.cc (expand_taskwait_call): Use
	BUILT_IN_GOMP_TASKWAIT_DEPEND_NOWAIT rather than
	BUILT_IN_GOMP_TASKWAIT_DEPEND if nowait clause is present.
gcc/c/
	* c-parser.cc (OMP_TASKWAIT_CLAUSE_MASK): Add nowait clause.
gcc/cp/
	* parser.cc (OMP_TASKWAIT_CLAUSE_MASK): Add nowait clause.
gcc/testsuite/
	* c-c++-common/gomp/taskwait-depend-nowait-1.c: New test.
libgomp/
	* libgomp_g.h (GOMP_taskwait_depend_nowait): Declare.
	* libgomp.map (GOMP_taskwait_depend_nowait): Export at GOMP_5.1.1.
	* task.c (empty_task): New function.
	(gomp_task_run_post_handle_depend_hash): Declare earlier.
	(gomp_task_run_post_handle_depend): Declare.
	(GOMP_task): Optimize fn == empty_task if there is nothing to wait
	for.
	(gomp_task_run_post_handle_dependers): Optimize task->fn == empty_task.
	(GOMP_taskwait_depend_nowait): New function.
	* testsuite/libgomp.c-c++-common/taskwait-depend-nowait-1.c: New test.

6 files changed, 53 insertions, 12 deletions

diff --git a/gcc/c/c-parser.cc b/gcc/c/c-parser.cc
index 8df8f60..492d995 100644
--- a/gcc/c/c-parser.cc
+++ b/gcc/c/c-parser.cc
@@ -20453,7 +20453,8 @@ c_parser_omp_task (location_t loc, c_parser *parser, bool *if_p)
 */
 
 #define OMP_TASKWAIT_CLAUSE_MASK					\
-	(OMP_CLAUSE_MASK_1 << PRAGMA_OMP_CLAUSE_DEPEND)
+	( (OMP_CLAUSE_MASK_1 << PRAGMA_OMP_CLAUSE_DEPEND)		\
+	| (OMP_CLAUSE_MASK_1 << PRAGMA_OMP_CLAUSE_NOWAIT))
 
 static void
 c_parser_omp_taskwait (c_parser *parser)
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 24585c1..868b861 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -43793,7 +43793,8 @@ cp_parser_omp_task (cp_parser *parser, cp_token *pragma_tok, bool *if_p)
    # pragma omp taskwait taskwait-clause[opt] new-line  */
 
 #define OMP_TASKWAIT_CLAUSE_MASK				\
-	(OMP_CLAUSE_MASK_1 << PRAGMA_OMP_CLAUSE_DEPEND)
+	( (OMP_CLAUSE_MASK_1 << PRAGMA_OMP_CLAUSE_DEPEND)	\
+	| (OMP_CLAUSE_MASK_1 << PRAGMA_OMP_CLAUSE_NOWAIT))
 
 static void
 cp_parser_omp_taskwait (cp_parser *parser, cp_token *pragma_tok)
diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
index 98f5544..cd17966 100644
--- a/gcc/gimplify.cc
+++ b/gcc/gimplify.cc
@@ -12319,17 +12319,34 @@ gimplify_omp_task (tree *expr_p, gimple_seq *pre_p)
   tree expr = *expr_p;
   gimple *g;
   gimple_seq body = NULL;
+  bool nowait = false;
+  bool has_depend = false;
 
   if (OMP_TASK_BODY (expr) == NULL_TREE)
-    for (tree c = OMP_TASK_CLAUSES (expr); c; c = OMP_CLAUSE_CHAIN (c))
-      if (OMP_CLAUSE_CODE (c) == OMP_CLAUSE_DEPEND
-	  && OMP_CLAUSE_DEPEND_KIND (c) == OMP_CLAUSE_DEPEND_MUTEXINOUTSET)
+    {
+      for (tree c = OMP_TASK_CLAUSES (expr); c; c = OMP_CLAUSE_CHAIN (c))
+	if (OMP_CLAUSE_CODE (c) == OMP_CLAUSE_DEPEND)
+	  {
+	    has_depend = true;
+	    if (OMP_CLAUSE_DEPEND_KIND (c) == OMP_CLAUSE_DEPEND_MUTEXINOUTSET)
+	      {
+		error_at (OMP_CLAUSE_LOCATION (c),
+			  "%<mutexinoutset%> kind in %<depend%> clause on a "
+			  "%<taskwait%> construct");
+		break;
+	      }
+	  }
+	else if (OMP_CLAUSE_CODE (c) == OMP_CLAUSE_NOWAIT)
+	  nowait = true;
+      if (nowait && !has_depend)
 	{
-	  error_at (OMP_CLAUSE_LOCATION (c),
-		    "%<mutexinoutset%> kind in %<depend%> clause on a "
-		    "%<taskwait%> construct");
-	  break;
+	  error_at (EXPR_LOCATION (expr),
+		    "%<taskwait%> construct with %<nowait%> clause but no "
+		    "%<depend%> clauses");
+	  *expr_p = NULL_TREE;
+	  return;
 	}
+    }
 
   gimplify_scan_omp_clauses (&OMP_TASK_CLAUSES (expr), pre_p,
 			     omp_find_clause (OMP_TASK_CLAUSES (expr),
diff --git a/gcc/omp-builtins.def b/gcc/omp-builtins.def
index cfa6483..ee5213e 100644
--- a/gcc/omp-builtins.def
+++ b/gcc/omp-builtins.def
@@ -89,6 +89,9 @@ DEF_GOMP_BUILTIN (BUILT_IN_GOMP_TASKWAIT, "GOMP_taskwait",
 		  BT_FN_VOID, ATTR_NOTHROW_LEAF_LIST)
 DEF_GOMP_BUILTIN (BUILT_IN_GOMP_TASKWAIT_DEPEND, "GOMP_taskwait_depend",
 		  BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
+DEF_GOMP_BUILTIN (BUILT_IN_GOMP_TASKWAIT_DEPEND_NOWAIT,
+		  "GOMP_taskwait_depend_nowait",
+		  BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
 DEF_GOMP_BUILTIN (BUILT_IN_GOMP_TASKYIELD, "GOMP_taskyield",
 		  BT_FN_VOID, ATTR_NOTHROW_LEAF_LIST)
 DEF_GOMP_BUILTIN (BUILT_IN_GOMP_TASKGROUP_START, "GOMP_taskgroup_start",
diff --git a/gcc/omp-expand.cc b/gcc/omp-expand.cc
index 5729a20..0821b8d 100644
--- a/gcc/omp-expand.cc
+++ b/gcc/omp-expand.cc
@@ -916,10 +916,12 @@ expand_taskwait_call (basic_block bb, gomp_task *entry_stmt)
 
   depend = OMP_CLAUSE_DECL (depend);
 
+  bool nowait = omp_find_clause (clauses, OMP_CLAUSE_NOWAIT) != NULL_TREE;
   gimple_stmt_iterator gsi = gsi_last_nondebug_bb (bb);
-  tree t
-    = build_call_expr (builtin_decl_explicit (BUILT_IN_GOMP_TASKWAIT_DEPEND),
-		       1, depend);
+  enum built_in_function f = (nowait
+			      ? BUILT_IN_GOMP_TASKWAIT_DEPEND_NOWAIT
+			      : BUILT_IN_GOMP_TASKWAIT_DEPEND);
+  tree t = build_call_expr (builtin_decl_explicit (f), 1, depend);
 
   force_gimple_operand_gsi (&gsi, t, true, NULL_TREE,
 			    false, GSI_CONTINUE_LINKING);
diff --git a/gcc/testsuite/c-c++-common/gomp/taskwait-depend-nowait-1.c b/gcc/testsuite/c-c++-common/gomp/taskwait-depend-nowait-1.c
new file mode 100644
index 0000000..54df023
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/gomp/taskwait-depend-nowait-1.c
@@ -0,0 +1,17 @@
+void
+foo (int *p)
+{
+  #pragma omp taskwait depend(iterator(i = 0:16) , in : p[i]) nowait depend(out : p[32])
+}
+
+void
+bar (int *p)
+{
+  #pragma omp taskwait depend(mutexinoutset : p[0]) nowait	/* { dg-error "'mutexinoutset' kind in 'depend' clause on a 'taskwait' construct" } */
+}
+
+void
+baz (void)
+{
+  #pragma omp taskwait nowait	/* { dg-error "'taskwait' construct with 'nowait' clause but no 'depend' clauses" } */
+}