[Ada] Refine checks for uplevel references

2018-05-25  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* exp_unst.adb (Visit_Node): Restrict check for uplevel references in
	prefixes of array attributes, to prefixes that are entity names whose
	type is constrained.
	(Note_Uplevel_Bound): Verify that the bound is declared in an enclosing
	subprogram, as itype created for loops in pre/postcondition may appear
	in loops at the library level.

From-SVN: r260717

gcc/ada/ChangeLog

 2018-05-25  Ed Schonberg  <schonberg@adacore.com>
 
+	* exp_unst.adb (Visit_Node): Restrict check for uplevel references in
+	prefixes of array attributes, to prefixes that are entity names whose
+	type is constrained.
+	(Note_Uplevel_Bound): Verify that the bound is declared in an enclosing
+	subprogram, as itype created for loops in pre/postcondition may appear
+	in loops at the library level.
+
+2018-05-25  Ed Schonberg  <schonberg@adacore.com>
+
 	* sem_ch13.adb (Build_Predicate_Functions): The predicate function
 	declaration is inserted into the tree and analyzed at that point, so
 	should not be reinserted when the body is constructed. Inside a

gcc/ada/exp_unst.adb

@@ -401,9 +401,14 @@ package body Exp_Unst is
                procedure Note_Uplevel_Bound (N : Node_Id) is
                begin
                   --  Entity name case
+                  --  Make sure that that the entity is declared in a
+                  --  subprogram. THis may not be the case for an type
+                  --  in a loop appearing in a precondition.
 
                   if Is_Entity_Name (N) then
-                     if Present (Entity (N)) then
+                     if Present (Entity (N))
+                        and then Present (Enclosing_Subprogram (Entity (N)))
+                     then
                         Note_Uplevel_Ref
                           (E      => Entity (N),
                            Caller => Current_Subprogram,
@@ -616,12 +621,26 @@ package body Exp_Unst is
                         | Attribute_Last
                         | Attribute_Length
                      =>
+                        --  Special-case attributes of array objects
+                        --  whose bounds may be uplevel references.
+                        --  More complex prefixes are handled during
+                        --  full traversal. Note that if the nominal
+                        --  subtype of the prefix is unconstrained, the
+                        --  bound must be obtained from the object, not
+                        --  from the (possibly) uplevel reference,
+
+                        if Is_Entity_Name (Prefix (N))
+                          and then Is_Constrained (Etype (Prefix (N)))
+                        then
                            declare
                               DT : Boolean := False;
                            begin
                               Check_Static_Type (Etype (Prefix (N)), DT);
                            end;
 
+                           return OK;
+                        end if;
+
                      when others =>
                         null;
                   end case;