atree.ads, atree.adb (Traverse_Func): Walk Field2 last, and eliminate the…

atree.ads, atree.adb (Traverse_Func): Walk Field2 last, and eliminate the resulting tail recursion by hand.

2007-12-19  Bob Duff  <duff@adacore.com>

	* atree.ads, atree.adb (Traverse_Func): Walk Field2 last, and eliminate
	the resulting tail recursion by hand. This prevents running out of
	memory on deeply nested concatenations, since Field2 is where the left
	operand of concatenations is stored.
	Fix bug (was returning OK_Orig in some cases). Fix return subtype to
	clarify that it can only return OK or Abandon.

	* sem_res.adb (Resolve_Op_Concat): Replace the recursion on the left
	operand by iteration, in order to avoid running out of memory on
	deeply-nested concatenations. Use the Parent pointer to get back up the
	tree.
	(Resolve_Op_Concat_Arg, Resolve_Op_Concat_First,
	 Resolve_Op_Concat_Rest): New procedures split out of
	Resolve_Op_Concat, so the iterative algorithm in Resolve_Op_Concat is
	clearer.

	* checks.adb (Remove_Checks): Use Traverse_Proc instead of
	Traverse_Func, because the former already takes care of discarding the
	result.

	* errout.adb (First_Node): Use Traverse_Proc instead of Traverse_Func,
	because the former already takes care of discarding the result.
	(Remove_Warning_Messages): Use appropriate subtype for Status and
	Discard

From-SVN: r131070

gcc/ada/atree.adb

@@ -2624,12 +2624,12 @@ package body Atree is
    -- Traverse_Func --
    -------------------
 
-   function Traverse_Func (Node : Node_Id) return Traverse_Result is
+   function Traverse_Func (Node : Node_Id) return Traverse_Final_Result is
 
       function Traverse_Field
         (Nod : Node_Id;
          Fld : Union_Id;
-         FN  : Field_Num) return Traverse_Result;
+         FN  : Field_Num) return Traverse_Final_Result;
       --  Fld is one of the fields of Nod. If the field points to syntactic
       --  node or list, then this node or list is traversed, and the result is
       --  the result of this traversal. Otherwise a value of True is returned
@@ -2642,7 +2642,7 @@ package body Atree is
       function Traverse_Field
         (Nod : Node_Id;
          Fld : Union_Id;
-         FN  : Field_Num) return Traverse_Result
+         FN  : Field_Num) return Traverse_Final_Result
       is
       begin
          if Fld = Union_Id (Empty) then
@@ -2697,10 +2697,21 @@ package body Atree is
          end if;
       end Traverse_Field;
 
+      Cur_Node : Node_Id := Node;
+
    --  Start of processing for Traverse_Func
 
    begin
-      case Process (Node) is
+      --  We walk Field2 last, and if it is a node, we eliminate the tail
+      --  recursion by jumping back to this label. This is because Field2 is
+      --  where the Left_Opnd field of N_Op_Concat is stored, and in practice
+      --  concatenations are sometimes deeply nested, as in X1&X2&...&XN. This
+      --  trick prevents us from running out of memory in that case. We don't
+      --  bother eliminating the tail recursion if Field2 is a list.
+
+      <<Tail_Recurse>>
+
+      case Process (Cur_Node) is
          when Abandon =>
             return Abandon;
 
@@ -2708,41 +2719,37 @@ package body Atree is
             return OK;
 
          when OK =>
-            if Traverse_Field (Node, Union_Id (Field1 (Node)), 1) = Abandon
-                 or else
-               Traverse_Field (Node, Union_Id (Field2 (Node)), 2) = Abandon
-                 or else
-               Traverse_Field (Node, Union_Id (Field3 (Node)), 3) = Abandon
-                 or else
-               Traverse_Field (Node, Union_Id (Field4 (Node)), 4) = Abandon
-                 or else
-               Traverse_Field (Node, Union_Id (Field5 (Node)), 5) = Abandon
-            then
-               return Abandon;
-            else
-               return OK;
-            end if;
+            null;
 
          when OK_Orig =>
-            declare
-               Onod : constant Node_Id := Original_Node (Node);
-            begin
-               if Traverse_Field (Onod, Union_Id (Field1 (Onod)), 1) = Abandon
-                    or else
-                  Traverse_Field (Onod, Union_Id (Field2 (Onod)), 2) = Abandon
-                    or else
-                  Traverse_Field (Onod, Union_Id (Field3 (Onod)), 3) = Abandon
-                    or else
-                  Traverse_Field (Onod, Union_Id (Field4 (Onod)), 4) = Abandon
-                    or else
-                  Traverse_Field (Onod, Union_Id (Field5 (Onod)), 5) = Abandon
-               then
-                  return Abandon;
-               else
-                  return OK_Orig;
-               end if;
-            end;
+            Cur_Node := Original_Node (Cur_Node);
       end case;
+
+      if Traverse_Field (Cur_Node, Field1 (Cur_Node), 1) = Abandon
+           or else  --  skip Field2 here
+         Traverse_Field (Cur_Node, Field3 (Cur_Node), 3) = Abandon
+           or else
+         Traverse_Field (Cur_Node, Field4 (Cur_Node), 4) = Abandon
+           or else
+         Traverse_Field (Cur_Node, Field5 (Cur_Node), 5) = Abandon
+      then
+         return Abandon;
+      end if;
+
+      if Field2 (Cur_Node) not in Node_Range then
+         return Traverse_Field (Cur_Node, Field2 (Cur_Node), 2);
+      elsif Is_Syntactic_Field (Nkind (Cur_Node), 2) and then
+        Field2 (Cur_Node) /= Empty_List_Or_Node
+      then
+         --  Here is the tail recursion step, we reset Cur_Node and jump
+         --  back to the start of the procedure, which has the same
+         --  semantic effect as a call.
+
+         Cur_Node := Node_Id (Field2 (Cur_Node));
+         goto Tail_Recurse;
+      end if;
+
+      return OK;
    end Traverse_Func;
 
    -------------------
@@ -2751,7 +2758,7 @@ package body Atree is
 
    procedure Traverse_Proc (Node : Node_Id) is
       function Traverse is new Traverse_Func (Process);
-      Discard : Traverse_Result;
+      Discard : Traverse_Final_Result;
       pragma Warnings (Off, Discard);
    begin
       Discard := Traverse (Node);

gcc/ada/atree.ads

@@ -503,18 +503,22 @@ package Atree is
    --  function is used only by Sinfo.CN to change nodes into their
    --  corresponding entities.
 
-   type Traverse_Result is (OK, OK_Orig, Skip, Abandon);
+   type Traverse_Result is (Abandon, OK, OK_Orig, Skip);
    --  This is the type of the result returned by the Process function passed
-   --  to Traverse_Func and Traverse_Proc and also the type of the result of
-   --  Traverse_Func itself. See descriptions below for details.
+   --  to Traverse_Func and Traverse_Proc. See below for details.
+
+   subtype Traverse_Final_Result is Traverse_Result range Abandon .. OK;
+   --  This is the type of the final result returned Traverse_Func, based on
+   --  the results of Process calls. See below for details.
 
    generic
      with function Process (N : Node_Id) return Traverse_Result is <>;
-   function Traverse_Func (Node : Node_Id) return Traverse_Result;
+   function Traverse_Func (Node : Node_Id) return Traverse_Final_Result;
    --  This is a generic function that, given the parent node for a subtree,
    --  traverses all syntactic nodes of this tree, calling the given function
-   --  Process on each one. The traversal is controlled as follows by the
-   --  result returned by Process:
+   --  Process on each one, in pre order (i.e. top-down). The order of
+   --  traversing subtrees is arbitrary. The traversal is controlled as follows
+   --  by the result returned by Process:
 
    --    OK       The traversal continues normally with the syntactic
    --             children of the node just processed.
@@ -537,7 +541,7 @@ package Atree is
      with function Process (N : Node_Id) return Traverse_Result is <>;
    procedure Traverse_Proc (Node : Node_Id);
    pragma Inline (Traverse_Proc);
-   --  This is similar to Traverse_Func except that no result is returned,
+   --  This is the same as Traverse_Func except that no result is returned,
    --  i.e. Traverse_Func is called and the result is simply discarded.
 
    ---------------------------

gcc/ada/checks.adb

@@ -2360,7 +2360,6 @@ package body Checks is
          Analyze_And_Resolve (N, Typ);
          return;
       end if;
-
    end Apply_Universal_Integer_Attribute_Checks;
 
    -------------------------------
@@ -5366,14 +5365,11 @@ package body Checks is
    -------------------
 
    procedure Remove_Checks (Expr : Node_Id) is
-      Discard : Traverse_Result;
-      pragma Warnings (Off, Discard);
-
       function Process (N : Node_Id) return Traverse_Result;
       --  Process a single node during the traversal
 
-      function Traverse is new Traverse_Func (Process);
-      --  The traversal function itself
+      procedure Traverse is new Traverse_Proc (Process);
+      --  The traversal procedure itself
 
       -------------
       -- Process --
@@ -5389,7 +5385,7 @@ package body Checks is
 
          case Nkind (N) is
             when N_And_Then =>
-               Discard := Traverse (Left_Opnd (N));
+               Traverse (Left_Opnd (N));
                return Skip;
 
             when N_Attribute_Reference =>
@@ -5425,7 +5421,7 @@ package body Checks is
                end case;
 
             when N_Or_Else =>
-               Discard := Traverse (Left_Opnd (N));
+               Traverse (Left_Opnd (N));
                return Skip;
 
             when N_Selected_Component =>
@@ -5446,7 +5442,7 @@ package body Checks is
    --  Start of processing for Remove_Checks
 
    begin
-      Discard := Traverse (Expr);
+      Traverse (Expr);
    end Remove_Checks;
 
    ----------------------------

gcc/ada/errout.adb

@@ -1235,15 +1235,12 @@ package body Errout is
       Sfile    : constant Source_File_Index := Get_Source_File_Index (L);
       Earliest : Node_Id;
       Eloc     : Source_Ptr;
-      Discard  : Traverse_Result;
-
-      pragma Warnings (Off, Discard);
 
       function Test_Earlier (N : Node_Id) return Traverse_Result;
       --  Function applied to every node in the construct
 
-      function Search_Tree_First is new Traverse_Func (Test_Earlier);
-      --  Create traversal function
+      procedure Search_Tree_First is new Traverse_Proc (Test_Earlier);
+      --  Create traversal procedure
 
       ------------------
       -- Test_Earlier --
@@ -1273,7 +1270,7 @@ package body Errout is
    begin
       Earliest := Original_Node (C);
       Eloc := Sloc (Earliest);
-      Discard := Search_Tree_First (Original_Node (C));
+      Search_Tree_First (Original_Node (C));
       return Earliest;
    end First_Node;
 
@@ -1982,7 +1979,7 @@ package body Errout is
             --  to the tree is harmless.
 
             declare
-               Status : Traverse_Result;
+               Status : Traverse_Final_Result;
 
             begin
                if Is_List_Member (N) then
@@ -2006,7 +2003,7 @@ package body Errout is
    begin
       if Warnings_Detected /= 0 then
          declare
-            Discard : Traverse_Result;
+            Discard : Traverse_Final_Result;
             pragma Warnings (Off, Discard);
 
          begin