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------------------------------------------------------------------------------
-- --
-- GNAT COMPILER COMPONENTS --
-- --
-- P A R . L A B L --
-- --
-- B o d y --
-- --
-- Copyright (C) 1992-2022, Free Software Foundation, Inc. --
-- --
-- GNAT is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
-- ware Foundation; either version 3, or (at your option) any later ver- --
-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
-- for more details. You should have received a copy of the GNU General --
-- Public License distributed with GNAT; see file COPYING3. If not, go to --
-- http://www.gnu.org/licenses for a complete copy of the license. --
-- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc. --
-- --
------------------------------------------------------------------------------
separate (Par)
procedure Labl is
Enclosing_Body_Or_Block : Node_Id;
-- Innermost enclosing body or block statement
Label_Decl_Node : Node_Id;
-- Implicit label declaration node
Defining_Ident_Node : Node_Id;
-- Defining identifier node for implicit label declaration
Next_Label_Elmt : Elmt_Id;
-- Next element on label element list
Label_Node : Node_Id;
-- Next label node to process
function Find_Enclosing_Body_Or_Block (N : Node_Id) return Node_Id;
-- Find the innermost body or block that encloses N
function Find_Enclosing_Body (N : Node_Id) return Node_Id;
-- Find the innermost body that encloses N
procedure Check_Distinct_Labels;
-- Checks the rule in RM-5.1(11), which requires distinct identifiers
-- for all the labels in a given body.
procedure Find_Natural_Loops;
-- Recognizes loops created by backward gotos, and rewrites the
-- corresponding statements into a proper loop, for optimization
-- purposes (for example, to control reclaiming local storage).
---------------------------
-- Check_Distinct_Labels --
---------------------------
procedure Check_Distinct_Labels is
Label_Id : constant Node_Id := Identifier (Label_Node);
Enclosing_Body : constant Node_Id :=
Find_Enclosing_Body (Enclosing_Body_Or_Block);
-- Innermost enclosing body
Next_Other_Label_Elmt : Elmt_Id := First_Elmt (Label_List);
-- Next element on label element list
Other_Label : Node_Id;
-- Next label node to process
begin
-- Loop through all the labels, and if we find some other label
-- (i.e. not Label_Node) that has the same identifier,
-- and whose innermost enclosing body is the same,
-- then we have an error.
-- Note that in the worst case, this is quadratic in the number
-- of labels. However, labels are not all that common, and this
-- is only called for explicit labels.
-- ???Nonetheless, the efficiency could be improved. For example,
-- call Labl for each body, rather than once per compilation.
while Present (Next_Other_Label_Elmt) loop
Other_Label := Node (Next_Other_Label_Elmt);
exit when Label_Node = Other_Label;
if Chars (Label_Id) = Chars (Identifier (Other_Label))
and then Enclosing_Body = Find_Enclosing_Body (Other_Label)
then
Error_Msg_Sloc := Sloc (Other_Label);
Error_Msg_N ("& conflicts with label#", Label_Id);
exit;
end if;
Next_Elmt (Next_Other_Label_Elmt);
end loop;
end Check_Distinct_Labels;
-------------------------
-- Find_Enclosing_Body --
-------------------------
function Find_Enclosing_Body (N : Node_Id) return Node_Id is
Result : Node_Id := N;
begin
-- This is the same as Find_Enclosing_Body_Or_Block, except
-- that we skip block statements and accept statements, instead
-- of stopping at them.
while Present (Result)
and then Nkind (Result) /= N_Entry_Body
and then Nkind (Result) /= N_Task_Body
and then Nkind (Result) /= N_Package_Body
and then Nkind (Result) /= N_Subprogram_Body
loop
Result := Parent (Result);
end loop;
return Result;
end Find_Enclosing_Body;
----------------------------------
-- Find_Enclosing_Body_Or_Block --
----------------------------------
function Find_Enclosing_Body_Or_Block (N : Node_Id) return Node_Id is
Result : Node_Id := Parent (N);
begin
-- Climb up the parent chain until we find a body or block
while Present (Result)
and then Nkind (Result) /= N_Accept_Statement
and then Nkind (Result) /= N_Entry_Body
and then Nkind (Result) /= N_Task_Body
and then Nkind (Result) /= N_Package_Body
and then Nkind (Result) /= N_Subprogram_Body
and then Nkind (Result) /= N_Block_Statement
loop
Result := Parent (Result);
end loop;
return Result;
end Find_Enclosing_Body_Or_Block;
------------------------
-- Find_Natural_Loops --
------------------------
procedure Find_Natural_Loops is
Node_List : constant Elist_Id := New_Elmt_List;
N : Elmt_Id;
Succ : Elmt_Id;
function Goto_Id (Goto_Node : Node_Id) return Name_Id;
-- Find Name_Id of goto statement, which may be an expanded name
function Matches
(Label_Node : Node_Id;
Goto_Node : Node_Id) return Boolean;
-- A label and a goto are candidates for a loop if the names match,
-- and both nodes appear in the same body. In addition, both must
-- appear in the same statement list. If they are not in the same
-- statement list, the goto is from within an nested structure, and
-- the label is not a header. We ignore the case where the goto is
-- within a conditional structure, and capture only infinite loops.
procedure Merge;
-- Merge labels and goto statements in order of increasing sloc value.
-- Discard labels of loop and block statements.
procedure No_Header (N : Elmt_Id);
-- The label N is known not to be a loop header. Scan forward and
-- remove all subsequent gotos that may have this node as a target.
procedure Process_Goto (N : Elmt_Id);
-- N is a forward jump. Scan forward and remove all subsequent gotos
-- that may have the same target, to preclude spurious loops.
procedure Rewrite_As_Loop
(Loop_Header : Node_Id;
Loop_End : Node_Id);
-- Given a label and a backwards goto, rewrite intervening statements
-- as a loop. Remove the label from the node list, and rewrite the
-- goto with the body of the new loop.
procedure Try_Loop (N : Elmt_Id);
-- N is a label that may be a loop header. Scan forward to find some
-- backwards goto with which to make a loop. Do nothing if there is
-- an intervening label that is not part of a loop, or more than one
-- goto with this target.
-------------
-- Goto_Id --
-------------
function Goto_Id (Goto_Node : Node_Id) return Name_Id is
begin
if Nkind (Name (Goto_Node)) = N_Identifier then
return Chars (Name (Goto_Node));
elsif Nkind (Name (Goto_Node)) = N_Selected_Component then
return Chars (Selector_Name (Name (Goto_Node)));
else
-- In case of error, return Id that can't match anything
return Name_Null;
end if;
end Goto_Id;
-------------
-- Matches --
-------------
function Matches
(Label_Node : Node_Id;
Goto_Node : Node_Id) return Boolean
is
begin
return Chars (Identifier (Label_Node)) = Goto_Id (Goto_Node)
and then Find_Enclosing_Body (Label_Node) =
Find_Enclosing_Body (Goto_Node);
end Matches;
-----------
-- Merge --
-----------
procedure Merge is
L1 : Elmt_Id;
G1 : Elmt_Id;
begin
L1 := First_Elmt (Label_List);
G1 := First_Elmt (Goto_List);
while Present (L1)
and then Present (G1)
loop
if Sloc (Node (L1)) < Sloc (Node (G1)) then
-- Optimization: remove labels of loops and blocks, which
-- play no role in what follows.
if Nkind (Node (L1)) /= N_Loop_Statement
and then Nkind (Node (L1)) /= N_Block_Statement
then
Append_Elmt (Node (L1), Node_List);
end if;
Next_Elmt (L1);
else
Append_Elmt (Node (G1), Node_List);
Next_Elmt (G1);
end if;
end loop;
while Present (L1) loop
Append_Elmt (Node (L1), Node_List);
Next_Elmt (L1);
end loop;
while Present (G1) loop
Append_Elmt (Node (G1), Node_List);
Next_Elmt (G1);
end loop;
end Merge;
---------------
-- No_Header --
---------------
procedure No_Header (N : Elmt_Id) is
S1, S2 : Elmt_Id;
begin
S1 := Next_Elmt (N);
while Present (S1) loop
S2 := Next_Elmt (S1);
if Nkind (Node (S1)) = N_Goto_Statement
and then Matches (Node (N), Node (S1))
then
Remove_Elmt (Node_List, S1);
end if;
S1 := S2;
end loop;
end No_Header;
------------------
-- Process_Goto --
------------------
procedure Process_Goto (N : Elmt_Id) is
Goto1 : constant Node_Id := Node (N);
Goto2 : Node_Id;
S, S1 : Elmt_Id;
begin
S := Next_Elmt (N);
while Present (S) loop
S1 := Next_Elmt (S);
Goto2 := Node (S);
if Nkind (Goto2) = N_Goto_Statement
and then Goto_Id (Goto1) = Goto_Id (Goto2)
and then Find_Enclosing_Body (Goto1) =
Find_Enclosing_Body (Goto2)
then
-- Goto2 may have the same target, remove it from
-- consideration.
Remove_Elmt (Node_List, S);
end if;
S := S1;
end loop;
end Process_Goto;
---------------------
-- Rewrite_As_Loop --
---------------------
procedure Rewrite_As_Loop
(Loop_Header : Node_Id;
Loop_End : Node_Id)
is
Loop_Body : constant List_Id := New_List;
Loop_Stmt : constant Node_Id :=
New_Node (N_Loop_Statement, Sloc (Loop_Header));
Stat : Node_Id;
Next_Stat : Node_Id;
begin
Stat := Next (Loop_Header);
while Stat /= Loop_End loop
Next_Stat := Next (Stat);
Remove (Stat);
Append (Stat, Loop_Body);
Stat := Next_Stat;
end loop;
Set_Statements (Loop_Stmt, Loop_Body);
Set_Identifier (Loop_Stmt, Identifier (Loop_Header));
Remove (Loop_Header);
Rewrite (Loop_End, Loop_Stmt);
Error_Msg_N
("info: code between label and backwards goto rewritten as loop??",
Loop_End);
end Rewrite_As_Loop;
--------------
-- Try_Loop --
--------------
procedure Try_Loop (N : Elmt_Id) is
Source : Elmt_Id;
Found : Boolean := False;
S1 : Elmt_Id;
begin
S1 := Next_Elmt (N);
while Present (S1) loop
if Nkind (Node (S1)) = N_Goto_Statement
and then Matches (Node (N), Node (S1))
then
if not Found then
-- If the label and the goto are both in the same statement
-- list, then we've found a loop. Note that labels and goto
-- statements are always part of some list, so In_Same_List
-- always makes sense.
if In_Same_List (Node (N), Node (S1)) then
Source := S1;
Found := True;
-- The goto is within some nested structure
else
No_Header (N);
return;
end if;
else
-- More than one goto with the same target
No_Header (N);
return;
end if;
elsif Nkind (Node (S1)) = N_Label
and then not Found
then
-- Intervening label before possible end of loop. Current
-- label is not a candidate. This is conservative, because
-- the label might not be the target of any jumps, but not
-- worth dealing with useless labels.
No_Header (N);
return;
else
-- If the node is a loop_statement, it corresponds to a
-- label-goto pair rewritten as a loop. Continue forward scan.
null;
end if;
Next_Elmt (S1);
end loop;
if Found then
Rewrite_As_Loop (Node (N), Node (Source));
Remove_Elmt (Node_List, N);
Remove_Elmt (Node_List, Source);
end if;
end Try_Loop;
begin
-- Start of processing for Find_Natural_Loops
Merge;
N := First_Elmt (Node_List);
while Present (N) loop
Succ := Next_Elmt (N);
if Nkind (Node (N)) = N_Label then
if No (Succ) then
exit;
elsif Nkind (Node (Succ)) = N_Label then
Try_Loop (Succ);
-- If a loop was found, the label has been removed, and
-- the following goto rewritten as the loop body.
Succ := Next_Elmt (N);
if Nkind (Node (Succ)) = N_Label then
-- Following label was not removed, so current label
-- is not a candidate header.
No_Header (N);
else
-- Following label was part of inner loop. Current
-- label is still a candidate.
Try_Loop (N);
Succ := Next_Elmt (N);
end if;
elsif Nkind (Node (Succ)) = N_Goto_Statement then
Try_Loop (N);
Succ := Next_Elmt (N);
end if;
elsif Nkind (Node (N)) = N_Goto_Statement then
Process_Goto (N);
Succ := Next_Elmt (N);
end if;
N := Succ;
end loop;
end Find_Natural_Loops;
-- Start of processing for Par.Labl
begin
Next_Label_Elmt := First_Elmt (Label_List);
while Present (Next_Label_Elmt) loop
Label_Node := Node (Next_Label_Elmt);
if not Comes_From_Source (Label_Node) then
goto Next_Label;
end if;
-- Find the innermost enclosing body or block, which is where
-- we need to implicitly declare this label
Enclosing_Body_Or_Block := Find_Enclosing_Body_Or_Block (Label_Node);
-- If we didn't find a parent, then the label in question never got
-- hooked into a reasonable declarative part. This happens only in
-- error situations, and we simply ignore the entry (we aren't going
-- to get into the semantics in any case given the error).
if Present (Enclosing_Body_Or_Block) then
Check_Distinct_Labels;
-- Now create the implicit label declaration node and its
-- corresponding defining identifier. Note that the defining
-- occurrence of a label is the implicit label declaration that
-- we are creating. The label itself is an applied occurrence.
Label_Decl_Node :=
New_Node (N_Implicit_Label_Declaration, Sloc (Label_Node));
Defining_Ident_Node :=
New_Entity (N_Defining_Identifier, Sloc (Identifier (Label_Node)));
Set_Chars (Defining_Ident_Node, Chars (Identifier (Label_Node)));
Set_Defining_Identifier (Label_Decl_Node, Defining_Ident_Node);
Set_Label_Construct (Label_Decl_Node, Label_Node);
-- The following makes sure that Comes_From_Source is appropriately
-- set for the entity, depending on whether the label appeared in
-- the source explicitly or not.
Set_Comes_From_Source
(Defining_Ident_Node, Comes_From_Source (Identifier (Label_Node)));
-- Now attach the implicit label declaration to the appropriate
-- declarative region, creating a declaration list if none exists
if No (Declarations (Enclosing_Body_Or_Block)) then
Set_Declarations (Enclosing_Body_Or_Block, New_List);
end if;
Append (Label_Decl_Node, Declarations (Enclosing_Body_Or_Block));
end if;
<<Next_Label>>
Next_Elmt (Next_Label_Elmt);
end loop;
Find_Natural_Loops;
end Labl;