[Ada] Incorrect Dynamic_Predicate results for static arguments

Message ID 20211011133947.GA1519068@adacore.com
State New
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  • [Ada] Incorrect Dynamic_Predicate results for static arguments
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Commit Message

Jason Merrill via Gcc-patches Oct. 11, 2021, 1:39 p.m.
In determining at run time whether a statically-known discrete value
satisifies the predicate of a subtype where both

   - a Dynamic_Predicate aspect specification applies (directly or
     indirectly) to a subtype; and

   - at least one other predicate aspect specification (that is, either
     a Static_Predicate aspect specification, a GNAT-defined Predicate
     aspect specification, or a second Dynamic_Predicate aspect
     specification) applies (directly or indirectly) to that same

sometimes only the "last" Dynamic_Predicate aspect's condition was
checked; the other predicate aspects were incorrectly ignored. This
could result in a subtype membership test incorrectly yielding a result
of True. This error is corrected.

Tested on x86_64-pc-linux-gnu, committed on trunk


	* exp_ch6.adb (Can_Fold_Predicate_Call): Do not attempt folding
	if there is more than one predicate involved. Recall that
	predicate aspect specification are additive, not overriding, and
	that there are three different predicate
	aspects (Dynamic_Predicate, Static_Predicate, and the
	GNAT-defined Predicate aspect). These various ways of
	introducing multiple predicates are all checked for.  A new
	nested function, Augments_Other_Dynamic_Predicate, is
	* sem_ch4.adb
	(Analyze_Indexed_Component_Form.Process_Function_Call): When
	determining whether a name like "X (Some_Discrete_Type)" might
	be interpreted as a slice, the answer should be "no" if the
	type/subtype name denotes the current instance of type/subtype.


diff --git a/gcc/ada/exp_ch6.adb b/gcc/ada/exp_ch6.adb
--- a/gcc/ada/exp_ch6.adb
+++ b/gcc/ada/exp_ch6.adb
@@ -3143,6 +3143,13 @@  package body Exp_Ch6 is
       function Can_Fold_Predicate_Call (P : Entity_Id) return Boolean is
          Actual : Node_Id;
+         function Augments_Other_Dynamic_Predicate (DP_Aspect_Spec : Node_Id)
+           return Boolean;
+         --  Given a Dynamic_Predicate aspect aspecification for a
+         --  discrete type, returns True iff another DP specification
+         --  applies (indirectly, via a subtype type or a derived type)
+         --  to the same entity that this aspect spec applies to.
          function May_Fold (N : Node_Id) return Traverse_Result;
          --  The predicate expression is foldable if it only contains operators
          --  and literals. During this check, we also replace occurrences of
@@ -3150,6 +3157,36 @@  package body Exp_Ch6 is
          --  value of the actual. This is done on a copy of the analyzed
          --  expression for the predicate.
+         --------------------------------------
+         -- Augments_Other_Dynamic_Predicate --
+         --------------------------------------
+         function Augments_Other_Dynamic_Predicate (DP_Aspect_Spec : Node_Id)
+           return Boolean
+         is
+            Aspect_Bearer : Entity_Id := Entity (DP_Aspect_Spec);
+         begin
+            loop
+               Aspect_Bearer := Nearest_Ancestor (Aspect_Bearer);
+               if not Present (Aspect_Bearer) then
+                  return False;
+               end if;
+               declare
+                  Aspect_Spec : constant Node_Id :=
+                    Find_Aspect (Aspect_Bearer, Aspect_Dynamic_Predicate);
+               begin
+                  if Present (Aspect_Spec)
+                    and then Aspect_Spec /= DP_Aspect_Spec
+                  then
+                     --  Found another Dynamic_Predicate aspect spec
+                     return True;
+                  end if;
+               end;
+            end loop;
+         end Augments_Other_Dynamic_Predicate;
          -- May_Fold --
@@ -3192,7 +3229,7 @@  package body Exp_Ch6 is
          function Try_Fold is new Traverse_Func (May_Fold);
-         --  Other lLocal variables
+         --  Other Local variables
          Subt   : constant Entity_Id := Etype (First_Entity (P));
          Aspect : Node_Id;
@@ -3220,6 +3257,11 @@  package body Exp_Ch6 is
            or else Nkind (Actual) /= N_Integer_Literal
            or else not Has_Dynamic_Predicate_Aspect (Subt)
            or else No (Aspect)
+           --  Do not fold if multiple applicable predicate aspects
+           or else Present (Find_Aspect (Subt, Aspect_Static_Predicate))
+           or else Present (Find_Aspect (Subt, Aspect_Predicate))
+           or else Augments_Other_Dynamic_Predicate (Aspect)
            or else CodePeer_Mode
             return False;

diff --git a/gcc/ada/sem_ch4.adb b/gcc/ada/sem_ch4.adb
--- a/gcc/ada/sem_ch4.adb
+++ b/gcc/ada/sem_ch4.adb
@@ -2534,6 +2534,7 @@  package body Sem_Ch4 is
               and then Is_Entity_Name (Actual)
               and then Is_Type (Entity (Actual))
               and then Is_Discrete_Type (Entity (Actual))
+              and then not Is_Current_Instance (Actual)
                Replace (N,
                  Make_Slice (Loc,