[Ada] Do not crash with -gnatR3 on Ghost aspects

2019-08-14  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_aux.adb (Next_Rep_Item): If a node in the rep chain
	involves a Ghost aspect it may have been replaced by a null
	statement; use the original node to find next Rep_Item.
	* repinfo.adb (List_Entities): Do not list an Ignored
	Ghost_Entity, for which information may have been deleted.

From-SVN: r274470

gcc/ada/ChangeLog

+2019-08-14  Ed Schonberg  <schonberg@adacore.com>
+
+	* sem_aux.adb (Next_Rep_Item): If a node in the rep chain
+	involves a Ghost aspect it may have been replaced by a null
+	statement; use the original node to find next Rep_Item.
+	* repinfo.adb (List_Entities): Do not list an Ignored
+	Ghost_Entity, for which information may have been deleted.
+
 2019-08-14  Bob Duff  <duff@adacore.com>
 
 	* sem_prag.ads, sem_prag.adb

gcc/ada/repinfo.adb

@@ -479,6 +479,7 @@ package body Repinfo is
 
       if Present (Ent)
         and then Nkind (Declaration_Node (Ent)) not in N_Renaming_Declaration
+        and then not Is_Ignored_Ghost_Entity (Ent)
       then
          --  If entity is a subprogram and we are listing mechanisms,
          --  then we need to list mechanisms for this entity. We skip this

gcc/ada/sem_aux.adb

@@ -569,6 +569,12 @@ package body Sem_Aux is
             elsif Entity (N) = E then
                return N;
             end if;
+
+         --  A Ghost-related aspect, if disabled, may have been replaced by a
+         --  null statement.
+
+         elsif Nkind (N) = N_Null_Statement then
+            N := Original_Node (N);
          end if;
 
          Next_Rep_Item (N);