OpenMP: Prepare omp-* for ancestor:1 handling

gcc/ChangeLog:

	* omp-expand.cc (expand_omp_target): Set device to
	GOMP_DEVICE_HOST_FALLBACK for ancestor.
	* omp-low.cc (scan_omp_target): Add 'omp target device_ancestor'
	attribute to generated target-region function for ancestor:1.
	* omp-offload.cc (pass_omp_target_link::execute): Don't nullify
	function pointer for ancestor:1.

 gcc/omp-expand.cc  | 6 +++++-
 gcc/omp-low.cc     | 6 ++++++
 gcc/omp-offload.cc | 9 +++++++++
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/gcc/omp-expand.cc b/gcc/omp-expand.cc
index 1023c56fc3d..dc0a963e9e3 100644
--- a/gcc/omp-expand.cc
+++ b/gcc/omp-expand.cc
@@ -10005,7 +10005,11 @@ expand_omp_target (struct omp_region *region)
 	    need_device_adjustment = true;
 	  device_loc = OMP_CLAUSE_LOCATION (c);
 	  if (OMP_CLAUSE_DEVICE_ANCESTOR (c))
-	    sorry_at (device_loc, "%<ancestor%> not yet supported");
+	    {
+	      device = build_int_cst (integer_type_node,
+				      GOMP_DEVICE_HOST_FALLBACK);
+	      sorry_at (device_loc, "%<ancestor%> not yet supported");
+	    }
 	}
       else
 	{
diff --git a/gcc/omp-low.cc b/gcc/omp-low.cc
index b9d5529f212..140ef229cc0 100644
--- a/gcc/omp-low.cc
+++ b/gcc/omp-low.cc
@@ -3094,6 +3094,12 @@ scan_omp_target (gomp_target *stmt, omp_context *outer_ctx)
   if (offloaded)
     {
       create_omp_child_function (ctx, false);
+      tree c = omp_find_clause (gimple_omp_target_clauses (ctx->stmt),
+				OMP_CLAUSE_DEVICE);
+      if (c && OMP_CLAUSE_DEVICE_ANCESTOR (c))
+	DECL_ATTRIBUTES (ctx->cb.dst_fn)
+	  = tree_cons (get_identifier ("omp target device_ancestor"),
+		       NULL_TREE, DECL_ATTRIBUTES (ctx->cb.dst_fn));
       gimple_omp_target_set_child_fn (stmt, ctx->cb.dst_fn);
     }
 
diff --git a/gcc/omp-offload.cc b/gcc/omp-offload.cc
index 3a89119371c..a6c108aef30 100644
--- a/gcc/omp-offload.cc
+++ b/gcc/omp-offload.cc
@@ -2803,6 +2803,15 @@ pass_omp_target_link::execute (function *fun)
 	{
 	  if (gimple_call_builtin_p (gsi_stmt (gsi), BUILT_IN_GOMP_TARGET))
 	    {
+	      tree dev = gimple_call_arg (gsi_stmt (gsi), 0);
+	      tree fn = gimple_call_arg (gsi_stmt (gsi), 1);
+	      if (POINTER_TYPE_P (TREE_TYPE (fn)))
+		fn = TREE_OPERAND (fn, 0);
+	      if (TREE_CODE (dev) == INTEGER_CST
+		  && wi::to_wide (dev) == GOMP_DEVICE_HOST_FALLBACK
+		  && lookup_attribute ("omp target device_ancestor",
+				       DECL_ATTRIBUTES (fn)) != NULL_TREE)
+		continue;  /* ancestor:1  */
 	      /* Nullify the second argument of __builtin_GOMP_target_ext.  */
 	      gimple_call_set_arg (gsi_stmt (gsi), 1, null_pointer_node);
 	      update_stmt (gsi_stmt (gsi));