[PATCH, OpenACC] Properly handle wait clause with no arguments

[Chung-Lin Tang <chunglin_tang@mentor.com>]

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Hi, this patch properly handles OpenACC 'wait' clauses without arguments, making it an equivalent of "wait all".
(current trunk basically discards and ignores such argument-less wait clauses)  This adds additional handling in
the pack/unpack of the wait argument across the compiler/libgomp interface, but is done in a matter that
doesn't affect binary compatibility.

This patch was part of the OpenACC async re-work that was done on the gomp4 branch (later merged to OG7/OG8), see [1].
I'm separating this part out and submitting it first because it's logically independent.

[1] https://gcc.gnu.org/ml/gcc-patches/2017-06/msg01842.html

Re-tested with offloading to ensure no regressions, is this okay for trunk?

Thanks,
Chung-Lin

2018-08-30  Chung-Lin Tang  <cltang@codesourcery.com>

         gcc/c/
         * c-parser.c (c_parser_oacc_clause_wait): Add representation of wait
         clause without argument as 'wait (GOMP_ASYNC_NOVAL)', adjust comments.

         gcc/cp/
         * parser.c (cp_parser_oacc_clause_wait): Add representation of wait
         clause without argument as 'wait (GOMP_ASYNC_NOVAL)', adjust comments.

         gcc/fortran/
         * trans-openmp.c (gfc_trans_omp_clauses_1): Add representation of wait
         clause without argument as 'wait (GOMP_ASYNC_NOVAL)'.

         gcc/
         * omp-low.c (expand_omp_target): Add middle-end support for handling
         OMP_CLAUSE_WAIT clause with a GOMP_ASYNC_NOVAL(-1) as the argument.

         include/
         * gomp-constants.h (GOMP_LAUNCH_OP_MASK): Define.
         (GOMP_LAUNCH_PACK): Add bitwise-and of GOMP_LAUNCH_OP_MASK.
         (GOMP_LAUNCH_OP): Likewise.

         libgomp/
         * oacc-parallel.c (GOACC_parallel_keyed): Interpret launch op as
         signed 16-bit field, adjust num_waits handling.
         (GOACC_enter_exit_data): Adjust num_waits handling.
         (GOACC_update): Adjust num_waits handling.

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Index: gcc/c/c-parser.c
===================================================================
--- gcc/c/c-parser.c	(revision 263981)
+++ gcc/c/c-parser.c	(working copy)
@@ -12719,7 +12719,7 @@ c_parser_oacc_clause_tile (c_parser *parser, tree
 }
 
 /* OpenACC:
-   wait ( int-expr-list ) */
+   wait [( int-expr-list )] */
 
 static tree
 c_parser_oacc_clause_wait (c_parser *parser, tree list)
@@ -12728,7 +12728,15 @@ c_parser_oacc_clause_wait (c_parser *parser, tree
 
   if (c_parser_peek_token (parser)->type == CPP_OPEN_PAREN)
     list = c_parser_oacc_wait_list (parser, clause_loc, list);
+  else
+    {
+      tree c = build_omp_clause (clause_loc, OMP_CLAUSE_WAIT);
 
+      OMP_CLAUSE_DECL (c) = build_int_cst (integer_type_node, GOMP_ASYNC_NOVAL);
+      OMP_CLAUSE_CHAIN (c) = list;
+      list = c;
+    }
+
   return list;
 }
 
Index: gcc/cp/parser.c
===================================================================
--- gcc/cp/parser.c	(revision 263981)
+++ gcc/cp/parser.c	(working copy)
@@ -32137,7 +32137,7 @@ cp_parser_oacc_wait_list (cp_parser *parser, locat
 }
 
 /* OpenACC:
-   wait ( int-expr-list ) */
+   wait [( int-expr-list )] */
 
 static tree
 cp_parser_oacc_clause_wait (cp_parser *parser, tree list)
@@ -32144,10 +32144,16 @@ cp_parser_oacc_clause_wait (cp_parser *parser, tre
 {
   location_t location = cp_lexer_peek_token (parser->lexer)->location;
 
-  if (cp_lexer_peek_token (parser->lexer)->type != CPP_OPEN_PAREN)
-    return list;
+  if (cp_lexer_peek_token (parser->lexer)->type == CPP_OPEN_PAREN)
+    list = cp_parser_oacc_wait_list (parser, location, list);
+  else
+    {
+      tree c = build_omp_clause (location, OMP_CLAUSE_WAIT);
 
-  list = cp_parser_oacc_wait_list (parser, location, list);
+      OMP_CLAUSE_DECL (c) = build_int_cst (integer_type_node, GOMP_ASYNC_NOVAL);
+      OMP_CLAUSE_CHAIN (c) = list;
+      list = c;
+    }
 
   return list;
 }
Index: gcc/fortran/trans-openmp.c
===================================================================
--- gcc/fortran/trans-openmp.c	(revision 263981)
+++ gcc/fortran/trans-openmp.c	(working copy)
@@ -2922,6 +2922,13 @@ gfc_trans_omp_clauses (stmtblock_t *block, gfc_omp
 	  omp_clauses = c;
 	}
     }
+  else if (clauses->wait)
+    {
+      c = build_omp_clause (where.lb->location, OMP_CLAUSE_WAIT);
+      OMP_CLAUSE_DECL (c) = build_int_cst (integer_type_node, GOMP_ASYNC_NOVAL);
+      OMP_CLAUSE_CHAIN (c) = omp_clauses;
+      omp_clauses = c;
+    }
   if (clauses->num_gangs_expr)
     {
       tree num_gangs_var
Index: gcc/omp-expand.c
===================================================================
--- gcc/omp-expand.c	(revision 263981)
+++ gcc/omp-expand.c	(working copy)
@@ -7381,16 +7381,32 @@ expand_omp_target (struct omp_region *region)
 	  /* ... push a placeholder.  */
 	  args.safe_push (integer_zero_node);
 
+	bool noval_seen = false;
+	tree noval = build_int_cst (integer_type_node, GOMP_ASYNC_NOVAL);
+
 	for (; c; c = OMP_CLAUSE_CHAIN (c))
 	  if (OMP_CLAUSE_CODE (c) == OMP_CLAUSE_WAIT)
 	    {
+	      tree wait_expr = OMP_CLAUSE_WAIT_EXPR (c);
+
+	      if (TREE_CODE (wait_expr) == INTEGER_CST
+		  && tree_int_cst_compare (wait_expr, noval) == 0)
+		{
+		  noval_seen = true;
+		  continue;
+		}
+
 	      args.safe_push (fold_convert_loc (OMP_CLAUSE_LOCATION (c),
-						integer_type_node,
-						OMP_CLAUSE_WAIT_EXPR (c)));
+						integer_type_node, wait_expr));
 	      num_waits++;
 	    }
 
-	if (!tagging || num_waits)
+	if (noval_seen && num_waits == 0)
+	  args[t_wait_idx] =
+	    (tagging
+	     ? oacc_launch_pack (GOMP_LAUNCH_WAIT, NULL_TREE, GOMP_ASYNC_NOVAL)
+	     : noval);
+	else if (!tagging || num_waits)
 	  {
 	    tree len;
 
Index: include/gomp-constants.h
===================================================================
--- include/gomp-constants.h	(revision 263981)
+++ include/gomp-constants.h	(working copy)
@@ -221,13 +221,14 @@ enum gomp_map_kind
 #define GOMP_LAUNCH_CODE_SHIFT	28
 #define GOMP_LAUNCH_DEVICE_SHIFT 16
 #define GOMP_LAUNCH_OP_SHIFT 0
+#define GOMP_LAUNCH_OP_MASK 0xffff
 #define GOMP_LAUNCH_PACK(CODE,DEVICE,OP)	\
   (((CODE) << GOMP_LAUNCH_CODE_SHIFT)		\
    | ((DEVICE) << GOMP_LAUNCH_DEVICE_SHIFT)	\
-   | ((OP) << GOMP_LAUNCH_OP_SHIFT))
+   | (((OP) & GOMP_LAUNCH_OP_MASK) << GOMP_LAUNCH_OP_SHIFT))
 #define GOMP_LAUNCH_CODE(X) (((X) >> GOMP_LAUNCH_CODE_SHIFT) & 0xf)
 #define GOMP_LAUNCH_DEVICE(X) (((X) >> GOMP_LAUNCH_DEVICE_SHIFT) & 0xfff)
-#define GOMP_LAUNCH_OP(X) (((X) >> GOMP_LAUNCH_OP_SHIFT) & 0xffff)
+#define GOMP_LAUNCH_OP(X) (((X) >> GOMP_LAUNCH_OP_SHIFT) & GOMP_LAUNCH_OP_MASK)
 #define GOMP_LAUNCH_OP_MAX 0xffff
 
 /* Bitmask to apply in order to find out the intended device of a target
Index: libgomp/oacc-parallel.c
===================================================================
--- libgomp/oacc-parallel.c	(revision 263981)
+++ libgomp/oacc-parallel.c	(working copy)
@@ -194,10 +194,14 @@ GOACC_parallel_keyed (int device, void (*fn) (void
 
 	case GOMP_LAUNCH_WAIT:
 	  {
-	    unsigned num_waits = GOMP_LAUNCH_OP (tag);
+	    /* Be careful to cast the op field as a signed 16-bit, and
+	       sign-extend to full integer.  */
+	    int num_waits = ((signed short) GOMP_LAUNCH_OP (tag));
 
-	    if (num_waits)
+	    if (num_waits > 0)
 	      goacc_wait (async, num_waits, &ap);
+	    else if (num_waits == acc_async_noval)
+	      acc_wait_all_async (async);
 	    break;
 	  }
 
@@ -351,7 +355,7 @@ GOACC_enter_exit_data (int device, size_t mapnum,
       || host_fallback)
     return;
 
-  if (num_waits)
+  if (num_waits > 0)
     {
       va_list ap;
 
@@ -359,6 +363,8 @@ GOACC_enter_exit_data (int device, size_t mapnum,
       goacc_wait (async, num_waits, &ap);
       va_end (ap);
     }
+  else if (num_waits == acc_async_noval)
+    acc_wait_all_async (async);
 
   /* Determine whether "finalize" semantics apply to all mappings of this
      OpenACC directive.  */
@@ -542,7 +548,7 @@ GOACC_update (int device, size_t mapnum,
       || host_fallback)
     return;
 
-  if (num_waits)
+  if (num_waits > 0)
     {
       va_list ap;
 
@@ -550,6 +556,8 @@ GOACC_update (int device, size_t mapnum,
       goacc_wait (async, num_waits, &ap);
       va_end (ap);
     }
+  else if (num_waits == acc_async_noval)
+    acc_wait_all_async (async);
 
   acc_dev->openacc.async_set_async_func (async);