544 lines
18 KiB
Ada
544 lines
18 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNAT COMPILER COMPONENTS --
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-- --
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-- P A R . L A B L --
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-- --
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-- B o d y --
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-- --
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-- Copyright (C) 1992-2020, Free Software Foundation, Inc. --
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-- --
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-- GNAT is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 3, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
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-- for more details. You should have received a copy of the GNU General --
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-- Public License distributed with GNAT; see file COPYING3. If not, go to --
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-- http://www.gnu.org/licenses for a complete copy of the license. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc. --
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-- --
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------------------------------------------------------------------------------
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separate (Par)
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procedure Labl is
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Enclosing_Body_Or_Block : Node_Id;
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-- Innermost enclosing body or block statement
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Label_Decl_Node : Node_Id;
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-- Implicit label declaration node
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Defining_Ident_Node : Node_Id;
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-- Defining identifier node for implicit label declaration
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Next_Label_Elmt : Elmt_Id;
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-- Next element on label element list
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Label_Node : Node_Id;
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-- Next label node to process
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function Find_Enclosing_Body_Or_Block (N : Node_Id) return Node_Id;
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-- Find the innermost body or block that encloses N
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function Find_Enclosing_Body (N : Node_Id) return Node_Id;
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-- Find the innermost body that encloses N
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procedure Check_Distinct_Labels;
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-- Checks the rule in RM-5.1(11), which requires distinct identifiers
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-- for all the labels in a given body.
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procedure Find_Natural_Loops;
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-- Recognizes loops created by backward gotos, and rewrites the
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-- corresponding statements into a proper loop, for optimization
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-- purposes (for example, to control reclaiming local storage).
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---------------------------
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-- Check_Distinct_Labels --
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---------------------------
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procedure Check_Distinct_Labels is
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Label_Id : constant Node_Id := Identifier (Label_Node);
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Enclosing_Body : constant Node_Id :=
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Find_Enclosing_Body (Enclosing_Body_Or_Block);
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-- Innermost enclosing body
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Next_Other_Label_Elmt : Elmt_Id := First_Elmt (Label_List);
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-- Next element on label element list
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Other_Label : Node_Id;
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-- Next label node to process
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begin
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-- Loop through all the labels, and if we find some other label
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-- (i.e. not Label_Node) that has the same identifier,
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-- and whose innermost enclosing body is the same,
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-- then we have an error.
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-- Note that in the worst case, this is quadratic in the number
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-- of labels. However, labels are not all that common, and this
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-- is only called for explicit labels.
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-- ???Nonetheless, the efficiency could be improved. For example,
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-- call Labl for each body, rather than once per compilation.
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while Present (Next_Other_Label_Elmt) loop
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Other_Label := Node (Next_Other_Label_Elmt);
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exit when Label_Node = Other_Label;
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if Chars (Label_Id) = Chars (Identifier (Other_Label))
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and then Enclosing_Body = Find_Enclosing_Body (Other_Label)
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then
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Error_Msg_Sloc := Sloc (Other_Label);
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Error_Msg_N ("& conflicts with label#", Label_Id);
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exit;
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end if;
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Next_Elmt (Next_Other_Label_Elmt);
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end loop;
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end Check_Distinct_Labels;
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-------------------------
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-- Find_Enclosing_Body --
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-------------------------
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function Find_Enclosing_Body (N : Node_Id) return Node_Id is
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Result : Node_Id := N;
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begin
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-- This is the same as Find_Enclosing_Body_Or_Block, except
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-- that we skip block statements and accept statements, instead
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-- of stopping at them.
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while Present (Result)
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and then Nkind (Result) /= N_Entry_Body
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and then Nkind (Result) /= N_Task_Body
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and then Nkind (Result) /= N_Package_Body
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and then Nkind (Result) /= N_Subprogram_Body
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loop
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Result := Parent (Result);
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end loop;
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return Result;
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end Find_Enclosing_Body;
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----------------------------------
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-- Find_Enclosing_Body_Or_Block --
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----------------------------------
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function Find_Enclosing_Body_Or_Block (N : Node_Id) return Node_Id is
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Result : Node_Id := Parent (N);
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begin
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-- Climb up the parent chain until we find a body or block
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while Present (Result)
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and then Nkind (Result) /= N_Accept_Statement
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and then Nkind (Result) /= N_Entry_Body
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and then Nkind (Result) /= N_Task_Body
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and then Nkind (Result) /= N_Package_Body
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and then Nkind (Result) /= N_Subprogram_Body
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and then Nkind (Result) /= N_Block_Statement
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loop
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Result := Parent (Result);
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end loop;
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return Result;
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end Find_Enclosing_Body_Or_Block;
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------------------------
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-- Find_Natural_Loops --
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------------------------
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procedure Find_Natural_Loops is
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Node_List : constant Elist_Id := New_Elmt_List;
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N : Elmt_Id;
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Succ : Elmt_Id;
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function Goto_Id (Goto_Node : Node_Id) return Name_Id;
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-- Find Name_Id of goto statement, which may be an expanded name
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function Matches
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(Label_Node : Node_Id;
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Goto_Node : Node_Id) return Boolean;
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-- A label and a goto are candidates for a loop if the names match,
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-- and both nodes appear in the same body. In addition, both must
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-- appear in the same statement list. If they are not in the same
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-- statement list, the goto is from within an nested structure, and
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-- the label is not a header. We ignore the case where the goto is
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-- within a conditional structure, and capture only infinite loops.
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procedure Merge;
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-- Merge labels and goto statements in order of increasing sloc value.
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-- Discard labels of loop and block statements.
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procedure No_Header (N : Elmt_Id);
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-- The label N is known not to be a loop header. Scan forward and
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-- remove all subsequent gotos that may have this node as a target.
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procedure Process_Goto (N : Elmt_Id);
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-- N is a forward jump. Scan forward and remove all subsequent gotos
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-- that may have the same target, to preclude spurious loops.
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procedure Rewrite_As_Loop
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(Loop_Header : Node_Id;
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Loop_End : Node_Id);
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-- Given a label and a backwards goto, rewrite intervening statements
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-- as a loop. Remove the label from the node list, and rewrite the
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-- goto with the body of the new loop.
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procedure Try_Loop (N : Elmt_Id);
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-- N is a label that may be a loop header. Scan forward to find some
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-- backwards goto with which to make a loop. Do nothing if there is
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-- an intervening label that is not part of a loop, or more than one
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-- goto with this target.
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-------------
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-- Goto_Id --
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-------------
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function Goto_Id (Goto_Node : Node_Id) return Name_Id is
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begin
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if Nkind (Name (Goto_Node)) = N_Identifier then
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return Chars (Name (Goto_Node));
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elsif Nkind (Name (Goto_Node)) = N_Selected_Component then
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return Chars (Selector_Name (Name (Goto_Node)));
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else
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-- In case of error, return Id that can't match anything
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return Name_Null;
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end if;
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end Goto_Id;
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-------------
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-- Matches --
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-------------
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function Matches
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(Label_Node : Node_Id;
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Goto_Node : Node_Id) return Boolean
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is
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begin
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return Chars (Identifier (Label_Node)) = Goto_Id (Goto_Node)
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and then Find_Enclosing_Body (Label_Node) =
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Find_Enclosing_Body (Goto_Node);
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end Matches;
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-----------
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-- Merge --
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-----------
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procedure Merge is
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L1 : Elmt_Id;
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G1 : Elmt_Id;
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begin
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L1 := First_Elmt (Label_List);
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G1 := First_Elmt (Goto_List);
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while Present (L1)
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and then Present (G1)
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loop
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if Sloc (Node (L1)) < Sloc (Node (G1)) then
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-- Optimization: remove labels of loops and blocks, which
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-- play no role in what follows.
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if Nkind (Node (L1)) /= N_Loop_Statement
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and then Nkind (Node (L1)) /= N_Block_Statement
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then
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Append_Elmt (Node (L1), Node_List);
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end if;
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Next_Elmt (L1);
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else
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Append_Elmt (Node (G1), Node_List);
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Next_Elmt (G1);
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end if;
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end loop;
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while Present (L1) loop
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Append_Elmt (Node (L1), Node_List);
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Next_Elmt (L1);
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end loop;
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while Present (G1) loop
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Append_Elmt (Node (G1), Node_List);
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Next_Elmt (G1);
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end loop;
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end Merge;
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---------------
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-- No_Header --
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---------------
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procedure No_Header (N : Elmt_Id) is
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S1, S2 : Elmt_Id;
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begin
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S1 := Next_Elmt (N);
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while Present (S1) loop
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S2 := Next_Elmt (S1);
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if Nkind (Node (S1)) = N_Goto_Statement
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and then Matches (Node (N), Node (S1))
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then
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Remove_Elmt (Node_List, S1);
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end if;
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S1 := S2;
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end loop;
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end No_Header;
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------------------
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-- Process_Goto --
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------------------
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procedure Process_Goto (N : Elmt_Id) is
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Goto1 : constant Node_Id := Node (N);
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Goto2 : Node_Id;
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S, S1 : Elmt_Id;
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begin
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S := Next_Elmt (N);
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while Present (S) loop
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S1 := Next_Elmt (S);
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Goto2 := Node (S);
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if Nkind (Goto2) = N_Goto_Statement
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and then Goto_Id (Goto1) = Goto_Id (Goto2)
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and then Find_Enclosing_Body (Goto1) =
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Find_Enclosing_Body (Goto2)
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then
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-- Goto2 may have the same target, remove it from
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-- consideration.
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Remove_Elmt (Node_List, S);
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end if;
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S := S1;
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end loop;
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end Process_Goto;
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---------------------
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-- Rewrite_As_Loop --
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---------------------
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procedure Rewrite_As_Loop
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(Loop_Header : Node_Id;
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Loop_End : Node_Id)
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is
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Loop_Body : constant List_Id := New_List;
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Loop_Stmt : constant Node_Id :=
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New_Node (N_Loop_Statement, Sloc (Loop_Header));
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Stat : Node_Id;
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Next_Stat : Node_Id;
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begin
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Stat := Next (Loop_Header);
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while Stat /= Loop_End loop
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Next_Stat := Next (Stat);
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Remove (Stat);
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Append (Stat, Loop_Body);
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Stat := Next_Stat;
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end loop;
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Set_Statements (Loop_Stmt, Loop_Body);
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Set_Identifier (Loop_Stmt, Identifier (Loop_Header));
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Remove (Loop_Header);
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Rewrite (Loop_End, Loop_Stmt);
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Error_Msg_N
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("info: code between label and backwards goto rewritten as loop??",
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Loop_End);
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end Rewrite_As_Loop;
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--------------
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-- Try_Loop --
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--------------
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procedure Try_Loop (N : Elmt_Id) is
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Source : Elmt_Id;
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Found : Boolean := False;
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S1 : Elmt_Id;
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begin
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S1 := Next_Elmt (N);
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while Present (S1) loop
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if Nkind (Node (S1)) = N_Goto_Statement
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and then Matches (Node (N), Node (S1))
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then
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if not Found then
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-- If the label and the goto are both in the same statement
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-- list, then we've found a loop. Note that labels and goto
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-- statements are always part of some list, so In_Same_List
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-- always makes sense.
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if In_Same_List (Node (N), Node (S1)) then
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Source := S1;
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Found := True;
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-- The goto is within some nested structure
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else
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No_Header (N);
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return;
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end if;
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else
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-- More than one goto with the same target
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No_Header (N);
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return;
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end if;
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elsif Nkind (Node (S1)) = N_Label
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and then not Found
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then
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-- Intervening label before possible end of loop. Current
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-- label is not a candidate. This is conservative, because
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-- the label might not be the target of any jumps, but not
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-- worth dealing with useless labels.
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No_Header (N);
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return;
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else
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-- If the node is a loop_statement, it corresponds to a
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-- label-goto pair rewritten as a loop. Continue forward scan.
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null;
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end if;
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Next_Elmt (S1);
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end loop;
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if Found then
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Rewrite_As_Loop (Node (N), Node (Source));
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Remove_Elmt (Node_List, N);
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Remove_Elmt (Node_List, Source);
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end if;
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end Try_Loop;
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begin
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-- Start of processing for Find_Natural_Loops
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Merge;
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N := First_Elmt (Node_List);
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while Present (N) loop
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Succ := Next_Elmt (N);
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if Nkind (Node (N)) = N_Label then
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if No (Succ) then
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exit;
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elsif Nkind (Node (Succ)) = N_Label then
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Try_Loop (Succ);
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-- If a loop was found, the label has been removed, and
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-- the following goto rewritten as the loop body.
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Succ := Next_Elmt (N);
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if Nkind (Node (Succ)) = N_Label then
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-- Following label was not removed, so current label
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-- is not a candidate header.
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No_Header (N);
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else
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-- Following label was part of inner loop. Current
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-- label is still a candidate.
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Try_Loop (N);
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Succ := Next_Elmt (N);
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end if;
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elsif Nkind (Node (Succ)) = N_Goto_Statement then
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Try_Loop (N);
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Succ := Next_Elmt (N);
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end if;
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elsif Nkind (Node (N)) = N_Goto_Statement then
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Process_Goto (N);
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Succ := Next_Elmt (N);
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end if;
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N := Succ;
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end loop;
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end Find_Natural_Loops;
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-- Start of processing for Par.Labl
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begin
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Next_Label_Elmt := First_Elmt (Label_List);
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while Present (Next_Label_Elmt) loop
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Label_Node := Node (Next_Label_Elmt);
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if not Comes_From_Source (Label_Node) then
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goto Next_Label;
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end if;
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-- Find the innermost enclosing body or block, which is where
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-- we need to implicitly declare this label
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Enclosing_Body_Or_Block := Find_Enclosing_Body_Or_Block (Label_Node);
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-- If we didn't find a parent, then the label in question never got
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-- hooked into a reasonable declarative part. This happens only in
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-- error situations, and we simply ignore the entry (we aren't going
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-- to get into the semantics in any case given the error).
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if Present (Enclosing_Body_Or_Block) then
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Check_Distinct_Labels;
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-- Now create the implicit label declaration node and its
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-- corresponding defining identifier. Note that the defining
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-- occurrence of a label is the implicit label declaration that
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-- we are creating. The label itself is an applied occurrence.
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Label_Decl_Node :=
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New_Node (N_Implicit_Label_Declaration, Sloc (Label_Node));
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Defining_Ident_Node :=
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New_Entity (N_Defining_Identifier, Sloc (Identifier (Label_Node)));
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Set_Chars (Defining_Ident_Node, Chars (Identifier (Label_Node)));
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Set_Defining_Identifier (Label_Decl_Node, Defining_Ident_Node);
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Set_Label_Construct (Label_Decl_Node, Label_Node);
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-- The following makes sure that Comes_From_Source is appropriately
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-- set for the entity, depending on whether the label appeared in
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-- the source explicitly or not.
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Set_Comes_From_Source
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(Defining_Ident_Node, Comes_From_Source (Identifier (Label_Node)));
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-- Now attach the implicit label declaration to the appropriate
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-- declarative region, creating a declaration list if none exists
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if No (Declarations (Enclosing_Body_Or_Block)) then
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Set_Declarations (Enclosing_Body_Or_Block, New_List);
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end if;
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Append (Label_Decl_Node, Declarations (Enclosing_Body_Or_Block));
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end if;
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<<Next_Label>>
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Next_Elmt (Next_Label_Elmt);
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end loop;
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Find_Natural_Loops;
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end Labl;
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