[Ada] tech debt: Parent (Empty) is not allowed

gcc/ada/

	* atree.adb, atree.ads (Parent, Set_Parent): Assert node is
	Present.
	(Copy_Parent, Parent_Kind): New helper routines.
	* gen_il-gen.adb: Add with clause.
	* nlists.adb (Parent): Assert Parent of list is Present.
	* aspects.adb, checks.adb, exp_aggr.adb, exp_ch6.adb,
	exp_util.adb, lib-xref-spark_specific.adb, osint.ads,
	sem_ch12.adb, sem_ch13.adb, sem_ch3.adb, sem_ch6.adb,
	sem_dim.adb, sem_prag.adb, sem_res.adb, sem_util.adb,
	treepr.adb: Do not call Parent and Set_Parent on the Empty node.
	* libgnat/a-stwiun__shared.adb, libgnat/a-stzunb__shared.adb:
	Minor: Fix typos in comments.
	* einfo.ads: Minor comment update.
	* sinfo-utils.ads, sinfo-utils.adb (Parent_Kind, Copy_Parent):
	New functions.

1 files changed, 6 insertions, 5 deletions

diff --git a/gcc/ada/nlists.adb b/gcc/ada/nlists.adb
index 821c0ab..7339c17 100644
--- a/gcc/ada/nlists.adb
+++ b/gcc/ada/nlists.adb
@@ -27,11 +27,11 @@
 --  file must be properly reflected in the corresponding C header a-nlists.h
 
 with Alloc;
-with Atree;          use Atree;
-with Debug;          use Debug;
-with Output;         use Output;
-with Sinfo;          use Sinfo;
-with Sinfo.Nodes;    use Sinfo.Nodes;
+with Atree;       use Atree;
+with Debug;       use Debug;
+with Output;      use Output;
+with Sinfo;       use Sinfo;
+with Sinfo.Nodes; use Sinfo.Nodes;
 with Table;
 
 package body Nlists is
@@ -1015,6 +1015,7 @@ package body Nlists is
 
    function Parent (List : List_Id) return Node_Or_Entity_Id is
    begin
+      pragma Assert (Present (List));
       pragma Assert (List <= Lists.Last);
       return Lists.Table (List).Parent;
    end Parent;