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------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- P A R . L A B L -- -- -- -- B o d y -- -- -- -- Copyright (C) 1992-2008, 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 ("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 Parent (Node (N)) = Parent (Node (S1)) then Source := S1; Found := True; else -- The goto is within some nested structure 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;
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