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------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- S E M _ C H 5 -- -- -- -- B o d y -- -- -- -- Copyright (C) 1992-2009, 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. -- -- -- ------------------------------------------------------------------------------ with Atree; use Atree; with Checks; use Checks; with Einfo; use Einfo; with Errout; use Errout; with Expander; use Expander; with Exp_Util; use Exp_Util; with Freeze; use Freeze; with Lib; use Lib; with Lib.Xref; use Lib.Xref; with Namet; use Namet; with Nlists; use Nlists; with Nmake; use Nmake; with Opt; use Opt; with Rtsfind; use Rtsfind; with Sem; use Sem; with Sem_Aux; use Sem_Aux; with Sem_Case; use Sem_Case; with Sem_Ch3; use Sem_Ch3; with Sem_Ch8; use Sem_Ch8; with Sem_Disp; use Sem_Disp; with Sem_Elab; use Sem_Elab; with Sem_Eval; use Sem_Eval; with Sem_Res; use Sem_Res; with Sem_SCIL; use Sem_SCIL; with Sem_Type; use Sem_Type; with Sem_Util; use Sem_Util; with Sem_Warn; use Sem_Warn; with Snames; use Snames; with Stand; use Stand; with Sinfo; use Sinfo; with Targparm; use Targparm; with Tbuild; use Tbuild; with Uintp; use Uintp; package body Sem_Ch5 is Unblocked_Exit_Count : Nat := 0; -- This variable is used when processing if statements, case statements, -- and block statements. It counts the number of exit points that are not -- blocked by unconditional transfer instructions: for IF and CASE, these -- are the branches of the conditional; for a block, they are the statement -- sequence of the block, and the statement sequences of any exception -- handlers that are part of the block. When processing is complete, if -- this count is zero, it means that control cannot fall through the IF, -- CASE or block statement. This is used for the generation of warning -- messages. This variable is recursively saved on entry to processing the -- construct, and restored on exit. ----------------------- -- Local Subprograms -- ----------------------- procedure Analyze_Iteration_Scheme (N : Node_Id); ------------------------ -- Analyze_Assignment -- ------------------------ procedure Analyze_Assignment (N : Node_Id) is Lhs : constant Node_Id := Name (N); Rhs : constant Node_Id := Expression (N); T1 : Entity_Id; T2 : Entity_Id; Decl : Node_Id; procedure Diagnose_Non_Variable_Lhs (N : Node_Id); -- N is the node for the left hand side of an assignment, and it is not -- a variable. This routine issues an appropriate diagnostic. procedure Kill_Lhs; -- This is called to kill current value settings of a simple variable -- on the left hand side. We call it if we find any error in analyzing -- the assignment, and at the end of processing before setting any new -- current values in place. procedure Set_Assignment_Type (Opnd : Node_Id; Opnd_Type : in out Entity_Id); -- Opnd is either the Lhs or Rhs of the assignment, and Opnd_Type -- is the nominal subtype. This procedure is used to deal with cases -- where the nominal subtype must be replaced by the actual subtype. ------------------------------- -- Diagnose_Non_Variable_Lhs -- ------------------------------- procedure Diagnose_Non_Variable_Lhs (N : Node_Id) is begin -- Not worth posting another error if left hand side already -- flagged as being illegal in some respect. if Error_Posted (N) then return; -- Some special bad cases of entity names elsif Is_Entity_Name (N) then declare Ent : constant Entity_Id := Entity (N); begin if Ekind (Ent) = E_In_Parameter then Error_Msg_N ("assignment to IN mode parameter not allowed", N); -- Renamings of protected private components are turned into -- constants when compiling a protected function. In the case -- of single protected types, the private component appears -- directly. elsif (Is_Prival (Ent) and then (Ekind (Current_Scope) = E_Function or else Ekind (Enclosing_Dynamic_Scope ( Current_Scope)) = E_Function)) or else (Ekind (Ent) = E_Component and then Is_Protected_Type (Scope (Ent))) then Error_Msg_N ("protected function cannot modify protected object", N); elsif Ekind (Ent) = E_Loop_Parameter then Error_Msg_N ("assignment to loop parameter not allowed", N); else Error_Msg_N ("left hand side of assignment must be a variable", N); end if; end; -- For indexed components or selected components, test prefix elsif Nkind (N) = N_Indexed_Component then Diagnose_Non_Variable_Lhs (Prefix (N)); -- Another special case for assignment to discriminant elsif Nkind (N) = N_Selected_Component then if Present (Entity (Selector_Name (N))) and then Ekind (Entity (Selector_Name (N))) = E_Discriminant then Error_Msg_N ("assignment to discriminant not allowed", N); else Diagnose_Non_Variable_Lhs (Prefix (N)); end if; else -- If we fall through, we have no special message to issue! Error_Msg_N ("left hand side of assignment must be a variable", N); end if; end Diagnose_Non_Variable_Lhs; -------------- -- Kill_LHS -- -------------- procedure Kill_Lhs is begin if Is_Entity_Name (Lhs) then declare Ent : constant Entity_Id := Entity (Lhs); begin if Present (Ent) then Kill_Current_Values (Ent); end if; end; end if; end Kill_Lhs; ------------------------- -- Set_Assignment_Type -- ------------------------- procedure Set_Assignment_Type (Opnd : Node_Id; Opnd_Type : in out Entity_Id) is begin Require_Entity (Opnd); -- If the assignment operand is an in-out or out parameter, then we -- get the actual subtype (needed for the unconstrained case). -- If the operand is the actual in an entry declaration, then within -- the accept statement it is replaced with a local renaming, which -- may also have an actual subtype. if Is_Entity_Name (Opnd) and then (Ekind (Entity (Opnd)) = E_Out_Parameter or else Ekind (Entity (Opnd)) = E_In_Out_Parameter or else Ekind (Entity (Opnd)) = E_Generic_In_Out_Parameter or else (Ekind (Entity (Opnd)) = E_Variable and then Nkind (Parent (Entity (Opnd))) = N_Object_Renaming_Declaration and then Nkind (Parent (Parent (Entity (Opnd)))) = N_Accept_Statement)) then Opnd_Type := Get_Actual_Subtype (Opnd); -- If assignment operand is a component reference, then we get the -- actual subtype of the component for the unconstrained case. elsif Nkind_In (Opnd, N_Selected_Component, N_Explicit_Dereference) and then not Is_Unchecked_Union (Opnd_Type) then Decl := Build_Actual_Subtype_Of_Component (Opnd_Type, Opnd); if Present (Decl) then Insert_Action (N, Decl); Mark_Rewrite_Insertion (Decl); Analyze (Decl); Opnd_Type := Defining_Identifier (Decl); Set_Etype (Opnd, Opnd_Type); Freeze_Itype (Opnd_Type, N); elsif Is_Constrained (Etype (Opnd)) then Opnd_Type := Etype (Opnd); end if; -- For slice, use the constrained subtype created for the slice elsif Nkind (Opnd) = N_Slice then Opnd_Type := Etype (Opnd); end if; end Set_Assignment_Type; -- Start of processing for Analyze_Assignment begin Mark_Coextensions (N, Rhs); Analyze (Rhs); Analyze (Lhs); -- Start type analysis for assignment T1 := Etype (Lhs); -- In the most general case, both Lhs and Rhs can be overloaded, and we -- must compute the intersection of the possible types on each side. if Is_Overloaded (Lhs) then declare I : Interp_Index; It : Interp; begin T1 := Any_Type; Get_First_Interp (Lhs, I, It); while Present (It.Typ) loop if Has_Compatible_Type (Rhs, It.Typ) then if T1 /= Any_Type then -- An explicit dereference is overloaded if the prefix -- is. Try to remove the ambiguity on the prefix, the -- error will be posted there if the ambiguity is real. if Nkind (Lhs) = N_Explicit_Dereference then declare PI : Interp_Index; PI1 : Interp_Index := 0; PIt : Interp; Found : Boolean; begin Found := False; Get_First_Interp (Prefix (Lhs), PI, PIt); while Present (PIt.Typ) loop if Is_Access_Type (PIt.Typ) and then Has_Compatible_Type (Rhs, Designated_Type (PIt.Typ)) then if Found then PIt := Disambiguate (Prefix (Lhs), PI1, PI, Any_Type); if PIt = No_Interp then Error_Msg_N ("ambiguous left-hand side" & " in assignment", Lhs); exit; else Resolve (Prefix (Lhs), PIt.Typ); end if; exit; else Found := True; PI1 := PI; end if; end if; Get_Next_Interp (PI, PIt); end loop; end; else Error_Msg_N ("ambiguous left-hand side in assignment", Lhs); exit; end if; else T1 := It.Typ; end if; end if; Get_Next_Interp (I, It); end loop; end; if T1 = Any_Type then Error_Msg_N ("no valid types for left-hand side for assignment", Lhs); Kill_Lhs; return; end if; end if; -- The resulting assignment type is T1, so now we will resolve the -- left hand side of the assignment using this determined type. Resolve (Lhs, T1); -- Cases where Lhs is not a variable if not Is_Variable (Lhs) then -- Ada 2005 (AI-327): Check assignment to the attribute Priority of -- a protected object. declare Ent : Entity_Id; S : Entity_Id; begin if Ada_Version >= Ada_05 then -- Handle chains of renamings Ent := Lhs; while Nkind (Ent) in N_Has_Entity and then Present (Entity (Ent)) and then Present (Renamed_Object (Entity (Ent))) loop Ent := Renamed_Object (Entity (Ent)); end loop; if (Nkind (Ent) = N_Attribute_Reference and then Attribute_Name (Ent) = Name_Priority) -- Renamings of the attribute Priority applied to protected -- objects have been previously expanded into calls to the -- Get_Ceiling run-time subprogram. or else (Nkind (Ent) = N_Function_Call and then (Entity (Name (Ent)) = RTE (RE_Get_Ceiling) or else Entity (Name (Ent)) = RTE (RO_PE_Get_Ceiling))) then -- The enclosing subprogram cannot be a protected function S := Current_Scope; while not (Is_Subprogram (S) and then Convention (S) = Convention_Protected) and then S /= Standard_Standard loop S := Scope (S); end loop; if Ekind (S) = E_Function and then Convention (S) = Convention_Protected then Error_Msg_N ("protected function cannot modify protected object", Lhs); end if; -- Changes of the ceiling priority of the protected object -- are only effective if the Ceiling_Locking policy is in -- effect (AARM D.5.2 (5/2)). if Locking_Policy /= 'C' then Error_Msg_N ("assignment to the attribute PRIORITY has " & "no effect?", Lhs); Error_Msg_N ("\since no Locking_Policy has been " & "specified", Lhs); end if; return; end if; end if; end; Diagnose_Non_Variable_Lhs (Lhs); return; -- Error of assigning to limited type. We do however allow this in -- certain cases where the front end generates the assignments. elsif Is_Limited_Type (T1) and then not Assignment_OK (Lhs) and then not Assignment_OK (Original_Node (Lhs)) and then not Is_Value_Type (T1) then -- CPP constructors can only be called in declarations if Is_CPP_Constructor_Call (Rhs) then Error_Msg_N ("invalid use of 'C'P'P constructor", Rhs); else Error_Msg_N ("left hand of assignment must not be limited type", Lhs); Explain_Limited_Type (T1, Lhs); end if; return; -- Enforce RM 3.9.3 (8): left-hand side cannot be abstract elsif Is_Interface (T1) and then not Is_Class_Wide_Type (T1) then Error_Msg_N ("target of assignment operation may not be abstract", Lhs); return; end if; -- Resolution may have updated the subtype, in case the left-hand -- side is a private protected component. Use the correct subtype -- to avoid scoping issues in the back-end. T1 := Etype (Lhs); -- Ada 2005 (AI-50217, AI-326): Check wrong dereference of incomplete -- type. For example: -- limited with P; -- package Pkg is -- type Acc is access P.T; -- end Pkg; -- with Pkg; use Acc; -- procedure Example is -- A, B : Acc; -- begin -- A.all := B.all; -- ERROR -- end Example; if Nkind (Lhs) = N_Explicit_Dereference and then Ekind (T1) = E_Incomplete_Type then Error_Msg_N ("invalid use of incomplete type", Lhs); Kill_Lhs; return; end if; -- Now we can complete the resolution of the right hand side Set_Assignment_Type (Lhs, T1); Resolve (Rhs, T1); -- This is the point at which we check for an unset reference Check_Unset_Reference (Rhs); Check_Unprotected_Access (Lhs, Rhs); -- Remaining steps are skipped if Rhs was syntactically in error if Rhs = Error then Kill_Lhs; return; end if; T2 := Etype (Rhs); if not Covers (T1, T2) then Wrong_Type (Rhs, Etype (Lhs)); Kill_Lhs; return; end if; -- Ada 2005 (AI-326): In case of explicit dereference of incomplete -- types, use the non-limited view if available if Nkind (Rhs) = N_Explicit_Dereference and then Ekind (T2) = E_Incomplete_Type and then Is_Tagged_Type (T2) and then Present (Non_Limited_View (T2)) then T2 := Non_Limited_View (T2); end if; Set_Assignment_Type (Rhs, T2); if Total_Errors_Detected /= 0 then if No (T1) then T1 := Any_Type; end if; if No (T2) then T2 := Any_Type; end if; end if; if T1 = Any_Type or else T2 = Any_Type then Kill_Lhs; return; end if; -- If the rhs is class-wide or dynamically tagged, then require the lhs -- to be class-wide. The case where the rhs is a dynamically tagged call -- to a dispatching operation with a controlling access result is -- excluded from this check, since the target has an access type (and -- no tag propagation occurs in that case). if (Is_Class_Wide_Type (T2) or else (Is_Dynamically_Tagged (Rhs) and then not Is_Access_Type (T1))) and then not Is_Class_Wide_Type (T1) then Error_Msg_N ("dynamically tagged expression not allowed!", Rhs); elsif Is_Class_Wide_Type (T1) and then not Is_Class_Wide_Type (T2) and then not Is_Tag_Indeterminate (Rhs) and then not Is_Dynamically_Tagged (Rhs) then Error_Msg_N ("dynamically tagged expression required!", Rhs); end if; -- Propagate the tag from a class-wide target to the rhs when the rhs -- is a tag-indeterminate call. if Is_Tag_Indeterminate (Rhs) then if Is_Class_Wide_Type (T1) then Propagate_Tag (Lhs, Rhs); elsif Nkind (Rhs) = N_Function_Call and then Is_Entity_Name (Name (Rhs)) and then Is_Abstract_Subprogram (Entity (Name (Rhs))) then Error_Msg_N ("call to abstract function must be dispatching", Name (Rhs)); elsif Nkind (Rhs) = N_Qualified_Expression and then Nkind (Expression (Rhs)) = N_Function_Call and then Is_Entity_Name (Name (Expression (Rhs))) and then Is_Abstract_Subprogram (Entity (Name (Expression (Rhs)))) then Error_Msg_N ("call to abstract function must be dispatching", Name (Expression (Rhs))); end if; end if; -- Ada 2005 (AI-385): When the lhs type is an anonymous access type, -- apply an implicit conversion of the rhs to that type to force -- appropriate static and run-time accessibility checks. This applies -- as well to anonymous access-to-subprogram types that are component -- subtypes or formal parameters. if Ada_Version >= Ada_05 and then Is_Access_Type (T1) then if Is_Local_Anonymous_Access (T1) or else Ekind (T2) = E_Anonymous_Access_Subprogram_Type then Rewrite (Rhs, Convert_To (T1, Relocate_Node (Rhs))); Analyze_And_Resolve (Rhs, T1); end if; end if; -- Ada 2005 (AI-231): Assignment to not null variable if Ada_Version >= Ada_05 and then Can_Never_Be_Null (T1) and then not Assignment_OK (Lhs) then -- Case where we know the right hand side is null if Known_Null (Rhs) then Apply_Compile_Time_Constraint_Error (N => Rhs, Msg => "(Ada 2005) null not allowed in null-excluding objects?", Reason => CE_Null_Not_Allowed); -- We still mark this as a possible modification, that's necessary -- to reset Is_True_Constant, and desirable for xref purposes. Note_Possible_Modification (Lhs, Sure => True); return; -- If we know the right hand side is non-null, then we convert to the -- target type, since we don't need a run time check in that case. elsif not Can_Never_Be_Null (T2) then Rewrite (Rhs, Convert_To (T1, Relocate_Node (Rhs))); Analyze_And_Resolve (Rhs, T1); end if; end if; if Is_Scalar_Type (T1) then Apply_Scalar_Range_Check (Rhs, Etype (Lhs)); -- For array types, verify that lengths match. If the right hand side -- if a function call that has been inlined, the assignment has been -- rewritten as a block, and the constraint check will be applied to the -- assignment within the block. elsif Is_Array_Type (T1) and then (Nkind (Rhs) /= N_Type_Conversion or else Is_Constrained (Etype (Rhs))) and then (Nkind (Rhs) /= N_Function_Call or else Nkind (N) /= N_Block_Statement) then -- Assignment verifies that the length of the Lsh and Rhs are equal, -- but of course the indices do not have to match. If the right-hand -- side is a type conversion to an unconstrained type, a length check -- is performed on the expression itself during expansion. In rare -- cases, the redundant length check is computed on an index type -- with a different representation, triggering incorrect code in -- the back end. Apply_Length_Check (Rhs, Etype (Lhs)); else -- Discriminant checks are applied in the course of expansion null; end if; -- Note: modifications of the Lhs may only be recorded after -- checks have been applied. Note_Possible_Modification (Lhs, Sure => True); -- ??? a real accessibility check is needed when ??? -- Post warning for redundant assignment or variable to itself if Warn_On_Redundant_Constructs -- We only warn for source constructs and then Comes_From_Source (N) -- Where the object is the same on both sides and then Same_Object (Lhs, Original_Node (Rhs)) -- But exclude the case where the right side was an operation -- that got rewritten (e.g. JUNK + K, where K was known to be -- zero). We don't want to warn in such a case, since it is -- reasonable to write such expressions especially when K is -- defined symbolically in some other package. and then Nkind (Original_Node (Rhs)) not in N_Op then if Nkind (Lhs) in N_Has_Entity then Error_Msg_NE ("?useless assignment of & to itself!", N, Entity (Lhs)); else Error_Msg_N ("?useless assignment of object to itself!", N); end if; end if; -- Check for non-allowed composite assignment if not Support_Composite_Assign_On_Target and then (Is_Array_Type (T1) or else Is_Record_Type (T1)) and then (not Has_Size_Clause (T1) or else Esize (T1) > 64) then Error_Msg_CRT ("composite assignment", N); end if; -- Check elaboration warning for left side if not in elab code if not In_Subprogram_Or_Concurrent_Unit then Check_Elab_Assign (Lhs); end if; -- Set Referenced_As_LHS if appropriate. We only set this flag if the -- assignment is a source assignment in the extended main source unit. -- We are not interested in any reference information outside this -- context, or in compiler generated assignment statements. if Comes_From_Source (N) and then In_Extended_Main_Source_Unit (Lhs) then Set_Referenced_Modified (Lhs, Out_Param => False); end if; -- Final step. If left side is an entity, then we may be able to -- reset the current tracked values to new safe values. We only have -- something to do if the left side is an entity name, and expansion -- has not modified the node into something other than an assignment, -- and of course we only capture values if it is safe to do so. if Is_Entity_Name (Lhs) and then Nkind (N) = N_Assignment_Statement then declare Ent : constant Entity_Id := Entity (Lhs); begin if Safe_To_Capture_Value (N, Ent) then -- If simple variable on left side, warn if this assignment -- blots out another one (rendering it useless) and note -- location of assignment in case no one references value. -- We only do this for source assignments, otherwise we can -- generate bogus warnings when an assignment is rewritten as -- another assignment, and gets tied up with itself. -- Note: we don't use Record_Last_Assignment here, because we -- have lots of other stuff to do under control of this test. if Warn_On_Modified_Unread and then Is_Assignable (Ent) and then Comes_From_Source (N) and then In_Extended_Main_Source_Unit (Ent) then Warn_On_Useless_Assignment (Ent, N); Set_Last_Assignment (Ent, Lhs); end if; -- If we are assigning an access type and the left side is an -- entity, then make sure that the Is_Known_[Non_]Null flags -- properly reflect the state of the entity after assignment. if Is_Access_Type (T1) then if Known_Non_Null (Rhs) then Set_Is_Known_Non_Null (Ent, True); elsif Known_Null (Rhs) and then not Can_Never_Be_Null (Ent) then Set_Is_Known_Null (Ent, True); else Set_Is_Known_Null (Ent, False); if not Can_Never_Be_Null (Ent) then Set_Is_Known_Non_Null (Ent, False); end if; end if; -- For discrete types, we may be able to set the current value -- if the value is known at compile time. elsif Is_Discrete_Type (T1) and then Compile_Time_Known_Value (Rhs) then Set_Current_Value (Ent, Rhs); else Set_Current_Value (Ent, Empty); end if; -- If not safe to capture values, kill them else Kill_Lhs; end if; end; end if; end Analyze_Assignment; ----------------------------- -- Analyze_Block_Statement -- ----------------------------- procedure Analyze_Block_Statement (N : Node_Id) is Decls : constant List_Id := Declarations (N); Id : constant Node_Id := Identifier (N); HSS : constant Node_Id := Handled_Statement_Sequence (N); begin -- If no handled statement sequence is present, things are really -- messed up, and we just return immediately (this is a defence -- against previous errors). if No (HSS) then return; end if; -- Normal processing with HSS present declare EH : constant List_Id := Exception_Handlers (HSS); Ent : Entity_Id := Empty; S : Entity_Id; Save_Unblocked_Exit_Count : constant Nat := Unblocked_Exit_Count; -- Recursively save value of this global, will be restored on exit begin -- Initialize unblocked exit count for statements of begin block -- plus one for each exception handler that is present. Unblocked_Exit_Count := 1; if Present (EH) then Unblocked_Exit_Count := Unblocked_Exit_Count + List_Length (EH); end if; -- If a label is present analyze it and mark it as referenced if Present (Id) then Analyze (Id); Ent := Entity (Id); -- An error defense. If we have an identifier, but no entity, -- then something is wrong. If we have previous errors, then -- just remove the identifier and continue, otherwise raise -- an exception. if No (Ent) then if Total_Errors_Detected /= 0 then Set_Identifier (N, Empty); else raise Program_Error; end if; else Set_Ekind (Ent, E_Block); Generate_Reference (Ent, N, ' '); Generate_Definition (Ent); if Nkind (Parent (Ent)) = N_Implicit_Label_Declaration then Set_Label_Construct (Parent (Ent), N); end if; end if; end if; -- If no entity set, create a label entity if No (Ent) then Ent := New_Internal_Entity (E_Block, Current_Scope, Sloc (N), 'B'); Set_Identifier (N, New_Occurrence_Of (Ent, Sloc (N))); Set_Parent (Ent, N); end if; Set_Etype (Ent, Standard_Void_Type); Set_Block_Node (Ent, Identifier (N)); Push_Scope (Ent); if Present (Decls) then Analyze_Declarations (Decls); Check_Completion; Inspect_Deferred_Constant_Completion (Decls); end if; Analyze (HSS); Process_End_Label (HSS, 'e', Ent); -- If exception handlers are present, then we indicate that -- enclosing scopes contain a block with handlers. We only -- need to mark non-generic scopes. if Present (EH) then S := Scope (Ent); loop Set_Has_Nested_Block_With_Handler (S); exit when Is_Overloadable (S) or else Ekind (S) = E_Package or else Is_Generic_Unit (S); S := Scope (S); end loop; end if; Check_References (Ent); Warn_On_Useless_Assignments (Ent); End_Scope; if Unblocked_Exit_Count = 0 then Unblocked_Exit_Count := Save_Unblocked_Exit_Count; Check_Unreachable_Code (N); else Unblocked_Exit_Count := Save_Unblocked_Exit_Count; end if; end; end Analyze_Block_Statement; ---------------------------- -- Analyze_Case_Statement -- ---------------------------- procedure Analyze_Case_Statement (N : Node_Id) is Exp : Node_Id; Exp_Type : Entity_Id; Exp_Btype : Entity_Id; Last_Choice : Nat; Dont_Care : Boolean; Others_Present : Boolean; pragma Warnings (Off, Last_Choice); pragma Warnings (Off, Dont_Care); -- Don't care about assigned values Statements_Analyzed : Boolean := False; -- Set True if at least some statement sequences get analyzed. -- If False on exit, means we had a serious error that prevented -- full analysis of the case statement, and as a result it is not -- a good idea to output warning messages about unreachable code. Save_Unblocked_Exit_Count : constant Nat := Unblocked_Exit_Count; -- Recursively save value of this global, will be restored on exit procedure Non_Static_Choice_Error (Choice : Node_Id); -- Error routine invoked by the generic instantiation below when -- the case statement has a non static choice. procedure Process_Statements (Alternative : Node_Id); -- Analyzes all the statements associated to a case alternative. -- Needed by the generic instantiation below. package Case_Choices_Processing is new Generic_Choices_Processing (Get_Alternatives => Alternatives, Get_Choices => Discrete_Choices, Process_Empty_Choice => No_OP, Process_Non_Static_Choice => Non_Static_Choice_Error, Process_Associated_Node => Process_Statements); use Case_Choices_Processing; -- Instantiation of the generic choice processing package ----------------------------- -- Non_Static_Choice_Error -- ----------------------------- procedure Non_Static_Choice_Error (Choice : Node_Id) is begin Flag_Non_Static_Expr ("choice given in case statement is not static!", Choice); end Non_Static_Choice_Error; ------------------------ -- Process_Statements -- ------------------------ procedure Process_Statements (Alternative : Node_Id) is Choices : constant List_Id := Discrete_Choices (Alternative); Ent : Entity_Id; begin Unblocked_Exit_Count := Unblocked_Exit_Count + 1; Statements_Analyzed := True; -- An interesting optimization. If the case statement expression -- is a simple entity, then we can set the current value within -- an alternative if the alternative has one possible value. -- case N is -- when 1 => alpha -- when 2 | 3 => beta -- when others => gamma -- Here we know that N is initially 1 within alpha, but for beta -- and gamma, we do not know anything more about the initial value. if Is_Entity_Name (Exp) then Ent := Entity (Exp); if Ekind (Ent) = E_Variable or else Ekind (Ent) = E_In_Out_Parameter or else Ekind (Ent) = E_Out_Parameter then if List_Length (Choices) = 1 and then Nkind (First (Choices)) in N_Subexpr and then Compile_Time_Known_Value (First (Choices)) then Set_Current_Value (Entity (Exp), First (Choices)); end if; Analyze_Statements (Statements (Alternative)); -- After analyzing the case, set the current value to empty -- since we won't know what it is for the next alternative -- (unless reset by this same circuit), or after the case. Set_Current_Value (Entity (Exp), Empty); return; end if; end if; -- Case where expression is not an entity name of a variable Analyze_Statements (Statements (Alternative)); end Process_Statements; -- Table to record choices. Put after subprograms since we make -- a call to Number_Of_Choices to get the right number of entries. Case_Table : Choice_Table_Type (1 .. Number_Of_Choices (N)); pragma Warnings (Off, Case_Table); -- Start of processing for Analyze_Case_Statement begin Unblocked_Exit_Count := 0; Exp := Expression (N); Analyze (Exp); -- The expression must be of any discrete type. In rare cases, the -- expander constructs a case statement whose expression has a private -- type whose full view is discrete. This can happen when generating -- a stream operation for a variant type after the type is frozen, -- when the partial of view of the type of the discriminant is private. -- In that case, use the full view to analyze case alternatives. if not Is_Overloaded (Exp) and then not Comes_From_Source (N) and then Is_Private_Type (Etype (Exp)) and then Present (Full_View (Etype (Exp))) and then Is_Discrete_Type (Full_View (Etype (Exp))) then Resolve (Exp, Etype (Exp)); Exp_Type := Full_View (Etype (Exp)); else Analyze_And_Resolve (Exp, Any_Discrete); Exp_Type := Etype (Exp); end if; Check_Unset_Reference (Exp); Exp_Btype := Base_Type (Exp_Type); -- The expression must be of a discrete type which must be determinable -- independently of the context in which the expression occurs, but -- using the fact that the expression must be of a discrete type. -- Moreover, the type this expression must not be a character literal -- (which is always ambiguous) or, for Ada-83, a generic formal type. -- If error already reported by Resolve, nothing more to do if Exp_Btype = Any_Discrete or else Exp_Btype = Any_Type then return; elsif Exp_Btype = Any_Character then Error_Msg_N ("character literal as case expression is ambiguous", Exp); return; elsif Ada_Version = Ada_83 and then (Is_Generic_Type (Exp_Btype) or else Is_Generic_Type (Root_Type (Exp_Btype))) then Error_Msg_N ("(Ada 83) case expression cannot be of a generic type", Exp); return; end if; -- If the case expression is a formal object of mode in out, then -- treat it as having a nonstatic subtype by forcing use of the base -- type (which has to get passed to Check_Case_Choices below). Also -- use base type when the case expression is parenthesized. if Paren_Count (Exp) > 0 or else (Is_Entity_Name (Exp) and then Ekind (Entity (Exp)) = E_Generic_In_Out_Parameter) then Exp_Type := Exp_Btype; end if; -- Call instantiated Analyze_Choices which does the rest of the work Analyze_Choices (N, Exp_Type, Case_Table, Last_Choice, Dont_Care, Others_Present); if Exp_Type = Universal_Integer and then not Others_Present then Error_Msg_N ("case on universal integer requires OTHERS choice", Exp); end if; -- If all our exits were blocked by unconditional transfers of control, -- then the entire CASE statement acts as an unconditional transfer of -- control, so treat it like one, and check unreachable code. Skip this -- test if we had serious errors preventing any statement analysis. if Unblocked_Exit_Count = 0 and then Statements_Analyzed then Unblocked_Exit_Count := Save_Unblocked_Exit_Count; Check_Unreachable_Code (N); else Unblocked_Exit_Count := Save_Unblocked_Exit_Count; end if; if not Expander_Active and then Compile_Time_Known_Value (Expression (N)) and then Serious_Errors_Detected = 0 then declare Chosen : constant Node_Id := Find_Static_Alternative (N); Alt : Node_Id; begin Alt := First (Alternatives (N)); while Present (Alt) loop if Alt /= Chosen then Remove_Warning_Messages (Statements (Alt)); end if; Next (Alt); end loop; end; end if; end Analyze_Case_Statement; ---------------------------- -- Analyze_Exit_Statement -- ---------------------------- -- If the exit includes a name, it must be the name of a currently open -- loop. Otherwise there must be an innermost open loop on the stack, -- to which the statement implicitly refers. procedure Analyze_Exit_Statement (N : Node_Id) is Target : constant Node_Id := Name (N); Cond : constant Node_Id := Condition (N); Scope_Id : Entity_Id; U_Name : Entity_Id; Kind : Entity_Kind; begin if No (Cond) then Check_Unreachable_Code (N); end if; if Present (Target) then Analyze (Target); U_Name := Entity (Target); if not In_Open_Scopes (U_Name) or else Ekind (U_Name) /= E_Loop then Error_Msg_N ("invalid loop name in exit statement", N); return; else Set_Has_Exit (U_Name); end if; else U_Name := Empty; end if; for J in reverse 0 .. Scope_Stack.Last loop Scope_Id := Scope_Stack.Table (J).Entity; Kind := Ekind (Scope_Id); if Kind = E_Loop and then (No (Target) or else Scope_Id = U_Name) then Set_Has_Exit (Scope_Id); exit; elsif Kind = E_Block or else Kind = E_Loop or else Kind = E_Return_Statement then null; else Error_Msg_N ("cannot exit from program unit or accept statement", N); exit; end if; end loop; -- Verify that if present the condition is a Boolean expression if Present (Cond) then Analyze_And_Resolve (Cond, Any_Boolean); Check_Unset_Reference (Cond); end if; -- Since the exit may take us out of a loop, any previous assignment -- statement is not useless, so clear last assignment indications. It -- is OK to keep other current values, since if the exit statement -- does not exit, then the current values are still valid. Kill_Current_Values (Last_Assignment_Only => True); end Analyze_Exit_Statement; ---------------------------- -- Analyze_Goto_Statement -- ---------------------------- procedure Analyze_Goto_Statement (N : Node_Id) is Label : constant Node_Id := Name (N); Scope_Id : Entity_Id; Label_Scope : Entity_Id; Label_Ent : Entity_Id; begin Check_Unreachable_Code (N); Kill_Current_Values (Last_Assignment_Only => True); Analyze (Label); Label_Ent := Entity (Label); -- Ignore previous error if Label_Ent = Any_Id then return; -- We just have a label as the target of a goto elsif Ekind (Label_Ent) /= E_Label then Error_Msg_N ("target of goto statement must be a label", Label); return; -- Check that the target of the goto is reachable according to Ada -- scoping rules. Note: the special gotos we generate for optimizing -- local handling of exceptions would violate these rules, but we mark -- such gotos as analyzed when built, so this code is never entered. elsif not Reachable (Label_Ent) then Error_Msg_N ("target of goto statement is not reachable", Label); return; end if; -- Here if goto passes initial validity checks Label_Scope := Enclosing_Scope (Label_Ent); for J in reverse 0 .. Scope_Stack.Last loop Scope_Id := Scope_Stack.Table (J).Entity; if Label_Scope = Scope_Id or else (Ekind (Scope_Id) /= E_Block and then Ekind (Scope_Id) /= E_Loop and then Ekind (Scope_Id) /= E_Return_Statement) then if Scope_Id /= Label_Scope then Error_Msg_N ("cannot exit from program unit or accept statement", N); end if; return; end if; end loop; raise Program_Error; end Analyze_Goto_Statement; -------------------------- -- Analyze_If_Statement -- -------------------------- -- A special complication arises in the analysis of if statements -- The expander has circuitry to completely delete code that it -- can tell will not be executed (as a result of compile time known -- conditions). In the analyzer, we ensure that code that will be -- deleted in this manner is analyzed but not expanded. This is -- obviously more efficient, but more significantly, difficulties -- arise if code is expanded and then eliminated (e.g. exception -- table entries disappear). Similarly, itypes generated in deleted -- code must be frozen from start, because the nodes on which they -- depend will not be available at the freeze point. procedure Analyze_If_Statement (N : Node_Id) is E : Node_Id; Save_Unblocked_Exit_Count : constant Nat := Unblocked_Exit_Count; -- Recursively save value of this global, will be restored on exit Save_In_Deleted_Code : Boolean; Del : Boolean := False; -- This flag gets set True if a True condition has been found, -- which means that remaining ELSE/ELSIF parts are deleted. procedure Analyze_Cond_Then (Cnode : Node_Id); -- This is applied to either the N_If_Statement node itself or -- to an N_Elsif_Part node. It deals with analyzing the condition -- and the THEN statements associated with it. ----------------------- -- Analyze_Cond_Then -- ----------------------- procedure Analyze_Cond_Then (Cnode : Node_Id) is Cond : constant Node_Id := Condition (Cnode); Tstm : constant List_Id := Then_Statements (Cnode); begin Unblocked_Exit_Count := Unblocked_Exit_Count + 1; Analyze_And_Resolve (Cond, Any_Boolean); Check_Unset_Reference (Cond); Set_Current_Value_Condition (Cnode); -- If already deleting, then just analyze then statements if Del then Analyze_Statements (Tstm); -- Compile time known value, not deleting yet elsif Compile_Time_Known_Value (Cond) then Save_In_Deleted_Code := In_Deleted_Code; -- If condition is True, then analyze the THEN statements -- and set no expansion for ELSE and ELSIF parts. if Is_True (Expr_Value (Cond)) then Analyze_Statements (Tstm); Del := True; Expander_Mode_Save_And_Set (False); In_Deleted_Code := True; -- If condition is False, analyze THEN with expansion off else -- Is_False (Expr_Value (Cond)) Expander_Mode_Save_And_Set (False); In_Deleted_Code := True; Analyze_Statements (Tstm); Expander_Mode_Restore; In_Deleted_Code := Save_In_Deleted_Code; end if; -- Not known at compile time, not deleting, normal analysis else Analyze_Statements (Tstm); end if; end Analyze_Cond_Then; -- Start of Analyze_If_Statement begin -- Initialize exit count for else statements. If there is no else -- part, this count will stay non-zero reflecting the fact that the -- uncovered else case is an unblocked exit. Unblocked_Exit_Count := 1; Analyze_Cond_Then (N); -- Now to analyze the elsif parts if any are present if Present (Elsif_Parts (N)) then E := First (Elsif_Parts (N)); while Present (E) loop Analyze_Cond_Then (E); Next (E); end loop; end if; if Present (Else_Statements (N)) then Analyze_Statements (Else_Statements (N)); end if; -- If all our exits were blocked by unconditional transfers of control, -- then the entire IF statement acts as an unconditional transfer of -- control, so treat it like one, and check unreachable code. if Unblocked_Exit_Count = 0 then Unblocked_Exit_Count := Save_Unblocked_Exit_Count; Check_Unreachable_Code (N); else Unblocked_Exit_Count := Save_Unblocked_Exit_Count; end if; if Del then Expander_Mode_Restore; In_Deleted_Code := Save_In_Deleted_Code; end if; if not Expander_Active and then Compile_Time_Known_Value (Condition (N)) and then Serious_Errors_Detected = 0 then if Is_True (Expr_Value (Condition (N))) then Remove_Warning_Messages (Else_Statements (N)); if Present (Elsif_Parts (N)) then E := First (Elsif_Parts (N)); while Present (E) loop Remove_Warning_Messages (Then_Statements (E)); Next (E); end loop; end if; else Remove_Warning_Messages (Then_Statements (N)); end if; end if; end Analyze_If_Statement; ---------------------------------------- -- Analyze_Implicit_Label_Declaration -- ---------------------------------------- -- An implicit label declaration is generated in the innermost -- enclosing declarative part. This is done for labels as well as -- block and loop names. -- Note: any changes in this routine may need to be reflected in -- Analyze_Label_Entity. procedure Analyze_Implicit_Label_Declaration (N : Node_Id) is Id : constant Node_Id := Defining_Identifier (N); begin Enter_Name (Id); Set_Ekind (Id, E_Label); Set_Etype (Id, Standard_Void_Type); Set_Enclosing_Scope (Id, Current_Scope); end Analyze_Implicit_Label_Declaration; ------------------------------ -- Analyze_Iteration_Scheme -- ------------------------------ procedure Analyze_Iteration_Scheme (N : Node_Id) is procedure Process_Bounds (R : Node_Id); -- If the iteration is given by a range, create temporaries and -- assignment statements block to capture the bounds and perform -- required finalization actions in case a bound includes a function -- call that uses the temporary stack. We first pre-analyze a copy of -- the range in order to determine the expected type, and analyze and -- resolve the original bounds. procedure Check_Controlled_Array_Attribute (DS : Node_Id); -- If the bounds are given by a 'Range reference on a function call -- that returns a controlled array, introduce an explicit declaration -- to capture the bounds, so that the function result can be finalized -- in timely fashion. -------------------- -- Process_Bounds -- -------------------- procedure Process_Bounds (R : Node_Id) is Loc : constant Source_Ptr := Sloc (N); R_Copy : constant Node_Id := New_Copy_Tree (R); Lo : constant Node_Id := Low_Bound (R); Hi : constant Node_Id := High_Bound (R); New_Lo_Bound : Node_Id := Empty; New_Hi_Bound : Node_Id := Empty; Typ : Entity_Id; Save_Analysis : Boolean; function One_Bound (Original_Bound : Node_Id; Analyzed_Bound : Node_Id) return Node_Id; -- Capture value of bound and return captured value --------------- -- One_Bound -- --------------- function One_Bound (Original_Bound : Node_Id; Analyzed_Bound : Node_Id) return Node_Id is Assign : Node_Id; Id : Entity_Id; Decl : Node_Id; begin -- If the bound is a constant or an object, no need for a separate -- declaration. If the bound is the result of previous expansion -- it is already analyzed and should not be modified. Note that -- the Bound will be resolved later, if needed, as part of the -- call to Make_Index (literal bounds may need to be resolved to -- type Integer). if Analyzed (Original_Bound) then return Original_Bound; elsif Nkind_In (Analyzed_Bound, N_Integer_Literal, N_Character_Literal) or else Is_Entity_Name (Analyzed_Bound) then Analyze_And_Resolve (Original_Bound, Typ); return Original_Bound; end if; -- Here we need to capture the value Analyze_And_Resolve (Original_Bound, Typ); Id := Make_Defining_Identifier (Loc, Chars => New_Internal_Name ('S')); -- Normally, the best approach is simply to generate a constant -- declaration that captures the bound. However, there is a nasty -- case where this is wrong. If the bound is complex, and has a -- possible use of the secondary stack, we need to generate a -- separate assignment statement to ensure the creation of a block -- which will release the secondary stack. -- We prefer the constant declaration, since it leaves us with a -- proper trace of the value, useful in optimizations that get rid -- of junk range checks. -- Probably we want something like the Side_Effect_Free routine -- in Exp_Util, but for now, we just optimize the cases of 'Last -- and 'First applied to an entity, since these are the important -- cases for range check optimizations. if Nkind (Original_Bound) = N_Attribute_Reference and then (Attribute_Name (Original_Bound) = Name_First or else Attribute_Name (Original_Bound) = Name_Last) and then Is_Entity_Name (Prefix (Original_Bound)) then Decl := Make_Object_Declaration (Loc, Defining_Identifier => Id, Constant_Present => True, Object_Definition => New_Occurrence_Of (Typ, Loc), Expression => Relocate_Node (Original_Bound)); Insert_Before (Parent (N), Decl); Analyze (Decl); Rewrite (Original_Bound, New_Occurrence_Of (Id, Loc)); return Expression (Decl); end if; -- Here we make a declaration with a separate assignment statement Decl := Make_Object_Declaration (Loc, Defining_Identifier => Id, Object_Definition => New_Occurrence_Of (Typ, Loc)); Insert_Before (Parent (N), Decl); Analyze (Decl); Assign := Make_Assignment_Statement (Loc, Name => New_Occurrence_Of (Id, Loc), Expression => Relocate_Node (Original_Bound)); -- If the relocated node is a function call then check if some -- SCIL node references it and needs readjustment. if Generate_SCIL and then Nkind (Original_Bound) = N_Function_Call then Adjust_SCIL_Node (Original_Bound, Expression (Assign)); end if; Insert_Before (Parent (N), Assign); Analyze (Assign); Rewrite (Original_Bound, New_Occurrence_Of (Id, Loc)); if Nkind (Assign) = N_Assignment_Statement then return Expression (Assign); else return Original_Bound; end if; end One_Bound; -- Start of processing for Process_Bounds begin -- Determine expected type of range by analyzing separate copy -- Do the analysis and resolution of the copy of the bounds with -- expansion disabled, to prevent the generation of finalization -- actions on each bound. This prevents memory leaks when the -- bounds contain calls to functions returning controlled arrays. Set_Parent (R_Copy, Parent (R)); Save_Analysis := Full_Analysis; Full_Analysis := False; Expander_Mode_Save_And_Set (False); Analyze (R_Copy); if Is_Overloaded (R_Copy) then -- Apply preference rules for range of predefined integer types, -- or diagnose true ambiguity. declare I : Interp_Index; It : Interp; Found : Entity_Id := Empty; begin Get_First_Interp (R_Copy, I, It); while Present (It.Typ) loop if Is_Discrete_Type (It.Typ) then if No (Found) then Found := It.Typ; else if Scope (Found) = Standard_Standard then null; elsif Scope (It.Typ) = Standard_Standard then Found := It.Typ; else -- Both of them are user-defined Error_Msg_N ("ambiguous bounds in range of iteration", R_Copy); Error_Msg_N ("\possible interpretations:", R_Copy); Error_Msg_NE ("\\} ", R_Copy, Found); Error_Msg_NE ("\\} ", R_Copy, It.Typ); exit; end if; end if; end if; Get_Next_Interp (I, It); end loop; end; end if; Resolve (R_Copy); Expander_Mode_Restore; Full_Analysis := Save_Analysis; Typ := Etype (R_Copy); -- If the type of the discrete range is Universal_Integer, then -- the bound's type must be resolved to Integer, and any object -- used to hold the bound must also have type Integer, unless the -- literal bounds are constant-folded expressions that carry a user- -- defined type. if Typ = Universal_Integer then if Nkind (Lo) = N_Integer_Literal and then Present (Etype (Lo)) and then Scope (Etype (Lo)) /= Standard_Standard then Typ := Etype (Lo); elsif Nkind (Hi) = N_Integer_Literal and then Present (Etype (Hi)) and then Scope (Etype (Hi)) /= Standard_Standard then Typ := Etype (Hi); else Typ := Standard_Integer; end if; end if; Set_Etype (R, Typ); New_Lo_Bound := One_Bound (Lo, Low_Bound (R_Copy)); New_Hi_Bound := One_Bound (Hi, High_Bound (R_Copy)); -- Propagate staticness to loop range itself, in case the -- corresponding subtype is static. if New_Lo_Bound /= Lo and then Is_Static_Expression (New_Lo_Bound) then Rewrite (Low_Bound (R), New_Copy (New_Lo_Bound)); end if; if New_Hi_Bound /= Hi and then Is_Static_Expression (New_Hi_Bound) then Rewrite (High_Bound (R), New_Copy (New_Hi_Bound)); end if; end Process_Bounds; -------------------------------------- -- Check_Controlled_Array_Attribute -- -------------------------------------- procedure Check_Controlled_Array_Attribute (DS : Node_Id) is begin if Nkind (DS) = N_Attribute_Reference and then Is_Entity_Name (Prefix (DS)) and then Ekind (Entity (Prefix (DS))) = E_Function and then Is_Array_Type (Etype (Entity (Prefix (DS)))) and then Is_Controlled ( Component_Type (Etype (Entity (Prefix (DS))))) and then Expander_Active then declare Loc : constant Source_Ptr := Sloc (N); Arr : constant Entity_Id := Etype (Entity (Prefix (DS))); Indx : constant Entity_Id := Base_Type (Etype (First_Index (Arr))); Subt : constant Entity_Id := Make_Defining_Identifier (Loc, New_Internal_Name ('S')); Decl : Node_Id; begin Decl := Make_Subtype_Declaration (Loc, Defining_Identifier => Subt, Subtype_Indication => Make_Subtype_Indication (Loc, Subtype_Mark => New_Reference_To (Indx, Loc), Constraint => Make_Range_Constraint (Loc, Relocate_Node (DS)))); Insert_Before (Parent (N), Decl); Analyze (Decl); Rewrite (DS, Make_Attribute_Reference (Loc, Prefix => New_Reference_To (Subt, Loc), Attribute_Name => Attribute_Name (DS))); Analyze (DS); end; end if; end Check_Controlled_Array_Attribute; -- Start of processing for Analyze_Iteration_Scheme begin -- For an infinite loop, there is no iteration scheme if No (N) then return; else declare Cond : constant Node_Id := Condition (N); begin -- For WHILE loop, verify that the condition is a Boolean -- expression and resolve and check it. if Present (Cond) then Analyze_And_Resolve (Cond, Any_Boolean); Check_Unset_Reference (Cond); Set_Current_Value_Condition (N); return; -- Else we have a FOR loop else declare LP : constant Node_Id := Loop_Parameter_Specification (N); Id : constant Entity_Id := Defining_Identifier (LP); DS : constant Node_Id := Discrete_Subtype_Definition (LP); begin Enter_Name (Id); -- We always consider the loop variable to be referenced, -- since the loop may be used just for counting purposes. Generate_Reference (Id, N, ' '); -- Check for case of loop variable hiding a local -- variable (used later on to give a nice warning -- if the hidden variable is never assigned). declare H : constant Entity_Id := Homonym (Id); begin if Present (H) and then Enclosing_Dynamic_Scope (H) = Enclosing_Dynamic_Scope (Id) and then Ekind (H) = E_Variable and then Is_Discrete_Type (Etype (H)) then Set_Hiding_Loop_Variable (H, Id); end if; end; -- Now analyze the subtype definition. If it is -- a range, create temporaries for bounds. if Nkind (DS) = N_Range and then Expander_Active then Process_Bounds (DS); else Analyze (DS); end if; if DS = Error then return; end if; -- The subtype indication may denote the completion -- of an incomplete type declaration. if Is_Entity_Name (DS) and then Present (Entity (DS)) and then Is_Type (Entity (DS)) and then Ekind (Entity (DS)) = E_Incomplete_Type then Set_Entity (DS, Get_Full_View (Entity (DS))); Set_Etype (DS, Entity (DS)); end if; if not Is_Discrete_Type (Etype (DS)) then Wrong_Type (DS, Any_Discrete); Set_Etype (DS, Any_Type); end if; Check_Controlled_Array_Attribute (DS); Make_Index (DS, LP); Set_Ekind (Id, E_Loop_Parameter); Set_Etype (Id, Etype (DS)); -- Treat a range as an implicit reference to the type, to -- inhibit spurious warnings. Generate_Reference (Base_Type (Etype (DS)), N, ' '); Set_Is_Known_Valid (Id, True); -- The loop is not a declarative part, so the only entity -- declared "within" must be frozen explicitly. declare Flist : constant List_Id := Freeze_Entity (Id, Sloc (N)); begin if Is_Non_Empty_List (Flist) then Insert_Actions (N, Flist); end if; end; -- Check for null or possibly null range and issue warning. -- We suppress such messages in generic templates and -- instances, because in practice they tend to be dubious -- in these cases. if Nkind (DS) = N_Range and then Comes_From_Source (N) then declare L : constant Node_Id := Low_Bound (DS); H : constant Node_Id := High_Bound (DS); begin -- If range of loop is null, issue warning if Compile_Time_Compare (L, H, Assume_Valid => True) = GT then -- Suppress the warning if inside a generic -- template or instance, since in practice -- they tend to be dubious in these cases since -- they can result from intended parametrization. if not Inside_A_Generic and then not In_Instance then -- Specialize msg if invalid values could make -- the loop non-null after all. if Compile_Time_Compare (L, H, Assume_Valid => False) = GT then Error_Msg_N ("?loop range is null, " & "loop will not execute", DS); -- Since we know the range of the loop is -- null, set the appropriate flag to remove -- the loop entirely during expansion. Set_Is_Null_Loop (Parent (N)); -- Here is where the loop could execute because -- of invalid values, so issue appropriate -- message and in this case we do not set the -- Is_Null_Loop flag since the loop may execute. else Error_Msg_N ("?loop range may be null, " & "loop may not execute", DS); Error_Msg_N ("?can only execute if invalid values " & "are present", DS); end if; end if; -- In either case, suppress warnings in the body of -- the loop, since it is likely that these warnings -- will be inappropriate if the loop never actually -- executes, which is unlikely. Set_Suppress_Loop_Warnings (Parent (N)); -- The other case for a warning is a reverse loop -- where the upper bound is the integer literal -- zero or one, and the lower bound can be positive. -- For example, we have -- for J in reverse N .. 1 loop -- In practice, this is very likely to be a case -- of reversing the bounds incorrectly in the range. elsif Reverse_Present (LP) and then Nkind (Original_Node (H)) = N_Integer_Literal and then (Intval (Original_Node (H)) = Uint_0 or else Intval (Original_Node (H)) = Uint_1) then Error_Msg_N ("?loop range may be null", DS); Error_Msg_N ("\?bounds may be wrong way round", DS); end if; end; end if; end; end if; end; end if; end Analyze_Iteration_Scheme; ------------------- -- Analyze_Label -- ------------------- -- Note: the semantic work required for analyzing labels (setting them as -- reachable) was done in a prepass through the statements in the block, -- so that forward gotos would be properly handled. See Analyze_Statements -- for further details. The only processing required here is to deal with -- optimizations that depend on an assumption of sequential control flow, -- since of course the occurrence of a label breaks this assumption. procedure Analyze_Label (N : Node_Id) is pragma Warnings (Off, N); begin Kill_Current_Values; end Analyze_Label; -------------------------- -- Analyze_Label_Entity -- -------------------------- procedure Analyze_Label_Entity (E : Entity_Id) is begin Set_Ekind (E, E_Label); Set_Etype (E, Standard_Void_Type); Set_Enclosing_Scope (E, Current_Scope); Set_Reachable (E, True); end Analyze_Label_Entity; ---------------------------- -- Analyze_Loop_Statement -- ---------------------------- procedure Analyze_Loop_Statement (N : Node_Id) is Loop_Statement : constant Node_Id := N; Id : constant Node_Id := Identifier (Loop_Statement); Iter : constant Node_Id := Iteration_Scheme (Loop_Statement); Ent : Entity_Id; begin if Present (Id) then -- Make name visible, e.g. for use in exit statements. Loop -- labels are always considered to be referenced. Analyze (Id); Ent := Entity (Id); -- Guard against serious error (typically, a scope mismatch when -- semantic analysis is requested) by creating loop entity to -- continue analysis. if No (Ent) then if Total_Errors_Detected /= 0 then Ent := New_Internal_Entity (E_Loop, Current_Scope, Sloc (Loop_Statement), 'L'); else raise Program_Error; end if; else Generate_Reference (Ent, Loop_Statement, ' '); Generate_Definition (Ent); -- If we found a label, mark its type. If not, ignore it, since it -- means we have a conflicting declaration, which would already -- have been diagnosed at declaration time. Set Label_Construct -- of the implicit label declaration, which is not created by the -- parser for generic units. if Ekind (Ent) = E_Label then Set_Ekind (Ent, E_Loop); if Nkind (Parent (Ent)) = N_Implicit_Label_Declaration then Set_Label_Construct (Parent (Ent), Loop_Statement); end if; end if; end if; -- Case of no identifier present else Ent := New_Internal_Entity (E_Loop, Current_Scope, Sloc (Loop_Statement), 'L'); Set_Etype (Ent, Standard_Void_Type); Set_Parent (Ent, Loop_Statement); end if; -- Kill current values on entry to loop, since statements in body of -- loop may have been executed before the loop is entered. Similarly we -- kill values after the loop, since we do not know that the body of the -- loop was executed. Kill_Current_Values; Push_Scope (Ent); Analyze_Iteration_Scheme (Iter); Analyze_Statements (Statements (Loop_Statement)); Process_End_Label (Loop_Statement, 'e', Ent); End_Scope; Kill_Current_Values; -- Check for infinite loop. We skip this check for generated code, since -- it justs waste time and makes debugging the routine called harder. if Comes_From_Source (N) then Check_Infinite_Loop_Warning (N); end if; -- Code after loop is unreachable if the loop has no WHILE or FOR -- and contains no EXIT statements within the body of the loop. if No (Iter) and then not Has_Exit (Ent) then Check_Unreachable_Code (N); end if; end Analyze_Loop_Statement; ---------------------------- -- Analyze_Null_Statement -- ---------------------------- -- Note: the semantics of the null statement is implemented by a single -- null statement, too bad everything isn't as simple as this! procedure Analyze_Null_Statement (N : Node_Id) is pragma Warnings (Off, N); begin null; end Analyze_Null_Statement; ------------------------ -- Analyze_Statements -- ------------------------ procedure Analyze_Statements (L : List_Id) is S : Node_Id; Lab : Entity_Id; begin -- The labels declared in the statement list are reachable from -- statements in the list. We do this as a prepass so that any -- goto statement will be properly flagged if its target is not -- reachable. This is not required, but is nice behavior! S := First (L); while Present (S) loop if Nkind (S) = N_Label then Analyze (Identifier (S)); Lab := Entity (Identifier (S)); -- If we found a label mark it as reachable if Ekind (Lab) = E_Label then Generate_Definition (Lab); Set_Reachable (Lab); if Nkind (Parent (Lab)) = N_Implicit_Label_Declaration then Set_Label_Construct (Parent (Lab), S); end if; -- If we failed to find a label, it means the implicit declaration -- of the label was hidden. A for-loop parameter can do this to -- a label with the same name inside the loop, since the implicit -- label declaration is in the innermost enclosing body or block -- statement. else Error_Msg_Sloc := Sloc (Lab); Error_Msg_N ("implicit label declaration for & is hidden#", Identifier (S)); end if; end if; Next (S); end loop; -- Perform semantic analysis on all statements Conditional_Statements_Begin; S := First (L); while Present (S) loop Analyze (S); Next (S); end loop; Conditional_Statements_End; -- Make labels unreachable. Visibility is not sufficient, because -- labels in one if-branch for example are not reachable from the -- other branch, even though their declarations are in the enclosing -- declarative part. S := First (L); while Present (S) loop if Nkind (S) = N_Label then Set_Reachable (Entity (Identifier (S)), False); end if; Next (S); end loop; end Analyze_Statements; ---------------------------- -- Check_Unreachable_Code -- ---------------------------- procedure Check_Unreachable_Code (N : Node_Id) is Error_Loc : Source_Ptr; P : Node_Id; begin if Is_List_Member (N) and then Comes_From_Source (N) then declare Nxt : Node_Id; begin Nxt := Original_Node (Next (N)); -- If a label follows us, then we never have dead code, since -- someone could branch to the label, so we just ignore it. if Nkind (Nxt) = N_Label then return; -- Otherwise see if we have a real statement following us elsif Present (Nxt) and then Comes_From_Source (Nxt) and then Is_Statement (Nxt) then -- Special very annoying exception. If we have a return that -- follows a raise, then we allow it without a warning, since -- the Ada RM annoyingly requires a useless return here! if Nkind (Original_Node (N)) /= N_Raise_Statement or else Nkind (Nxt) /= N_Simple_Return_Statement then -- The rather strange shenanigans with the warning message -- here reflects the fact that Kill_Dead_Code is very good -- at removing warnings in deleted code, and this is one -- warning we would prefer NOT to have removed. Error_Loc := Sloc (Nxt); -- If we have unreachable code, analyze and remove the -- unreachable code, since it is useless and we don't -- want to generate junk warnings. -- We skip this step if we are not in code generation mode. -- This is the one case where we remove dead code in the -- semantics as opposed to the expander, and we do not want -- to remove code if we are not in code generation mode, -- since this messes up the ASIS trees. -- Note that one might react by moving the whole circuit to -- exp_ch5, but then we lose the warning in -gnatc mode. if Operating_Mode = Generate_Code then loop Nxt := Next (N); -- Quit deleting when we have nothing more to delete -- or if we hit a label (since someone could transfer -- control to a label, so we should not delete it). exit when No (Nxt) or else Nkind (Nxt) = N_Label; -- Statement/declaration is to be deleted Analyze (Nxt); Remove (Nxt); Kill_Dead_Code (Nxt); end loop; end if; -- Now issue the warning Error_Msg ("?unreachable code!", Error_Loc); end if; -- If the unconditional transfer of control instruction is -- the last statement of a sequence, then see if our parent -- is one of the constructs for which we count unblocked exits, -- and if so, adjust the count. else P := Parent (N); -- Statements in THEN part or ELSE part of IF statement if Nkind (P) = N_If_Statement then null; -- Statements in ELSIF part of an IF statement elsif Nkind (P) = N_Elsif_Part then P := Parent (P); pragma Assert (Nkind (P) = N_If_Statement); -- Statements in CASE statement alternative elsif Nkind (P) = N_Case_Statement_Alternative then P := Parent (P); pragma Assert (Nkind (P) = N_Case_Statement); -- Statements in body of block elsif Nkind (P) = N_Handled_Sequence_Of_Statements and then Nkind (Parent (P)) = N_Block_Statement then null; -- Statements in exception handler in a block elsif Nkind (P) = N_Exception_Handler and then Nkind (Parent (P)) = N_Handled_Sequence_Of_Statements and then Nkind (Parent (Parent (P))) = N_Block_Statement then null; -- None of these cases, so return else return; end if; -- This was one of the cases we are looking for (i.e. the -- parent construct was IF, CASE or block) so decrement count. Unblocked_Exit_Count := Unblocked_Exit_Count - 1; end if; end; end if; end Check_Unreachable_Code; end Sem_Ch5;
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