------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- S E M _ C H 5 -- -- -- -- B o d y -- -- -- -- -- -- Copyright (C) 1992-2002 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 2, 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 COPYING. If not, write -- -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, -- -- MA 02111-1307, USA. -- -- -- -- 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.Xref; use Lib.Xref; with Nlists; use Nlists; with Opt; use Opt; with Sem; use Sem; 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_Eval; use Sem_Eval; with Sem_Res; use Sem_Res; with Sem_Type; use Sem_Type; with Sem_Util; use Sem_Util; with Sem_Warn; use Sem_Warn; with Stand; use Stand; with Sinfo; use Sinfo; 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 or case -- statements, it counts the number of branches of the conditional -- that are not blocked by unconditional transfer instructions. At -- the end of processing, if the count is zero, it means that control -- cannot fall through the conditional statement. This is used for -- the generation of warning messages. This variable is recursively -- saved on entry to processing an if or case, 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, 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 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 if Ekind (Entity (N)) = E_In_Parameter then Error_Msg_N ("assignment to IN mode parameter not allowed", N); return; -- Private declarations in a protected object are turned into -- constants when compiling a protected function. elsif Present (Scope (Entity (N))) and then Is_Protected_Type (Scope (Entity (N))) and then (Ekind (Current_Scope) = E_Function or else Ekind (Enclosing_Dynamic_Scope (Current_Scope)) = E_Function) then Error_Msg_N ("protected function cannot modify protected object", N); return; elsif Ekind (Entity (N)) = E_Loop_Parameter then Error_Msg_N ("assignment to loop parameter not allowed", N); return; end if; -- For indexed components, or selected components, test prefix elsif Nkind (N) = N_Indexed_Component or else Nkind (N) = N_Selected_Component then Diagnose_Non_Variable_Lhs (Prefix (N)); return; end if; -- 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 Diagnose_Non_Variable_Lhs; ------------------------- -- Set_Assignment_Type -- ------------------------- procedure Set_Assignment_Type (Opnd : Node_Id; Opnd_Type : in out Entity_Id) is begin -- If the assignment operand is an in-out or out parameter, then we -- get the actual subtype (needed for the unconstrained case). 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) 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 (Opnd) = N_Selected_Component or else Nkind (Opnd) = N_Explicit_Dereference 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 Analyze (Rhs); Analyze (Lhs); 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 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 return; 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); return; end if; end if; Resolve (Lhs, T1); if not Is_Variable (Lhs) then Diagnose_Non_Variable_Lhs (Lhs); return; elsif Is_Limited_Type (T1) and then not Assignment_OK (Lhs) and then not Assignment_OK (Original_Node (Lhs)) then Error_Msg_N ("left hand of assignment must not be limited type", 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); Set_Assignment_Type (Lhs, T1); Resolve (Rhs, T1); -- Remaining steps are skipped if Rhs was synatactically in error if Rhs = Error then return; end if; T2 := Etype (Rhs); Check_Unset_Reference (Rhs); Note_Possible_Modification (Lhs); if Covers (T1, T2) then null; else Wrong_Type (Rhs, Etype (Lhs)); return; end if; Set_Assignment_Type (Rhs, T2); if T1 = Any_Type or else T2 = Any_Type then return; end if; if (Is_Class_Wide_Type (T2) or else Is_Dynamically_Tagged (Rhs)) 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; -- Tag propagation is done only in semantics mode only. If expansion -- is on, the rhs tag indeterminate function call has been expanded -- and tag propagation would have happened too late, so the -- propagation take place in expand_call instead. if not Expander_Active and then Is_Class_Wide_Type (T1) and then Is_Tag_Indeterminate (Rhs) then Propagate_Tag (Lhs, Rhs); end if; if Is_Scalar_Type (T1) then Apply_Scalar_Range_Check (Rhs, Etype (Lhs)); elsif Is_Array_Type (T1) then -- Assignment verifies that the length of the Lsh and Rhs are equal, -- but of course the indices do not have to match. Apply_Length_Check (Rhs, Etype (Lhs)); else -- Discriminant checks are applied in the course of expansion. null; end if; -- ??? a real accessibility check is needed when ??? -- Post warning for useless assignment if Warn_On_Redundant_Constructs -- We only warn for source constructs and then Comes_From_Source (N) -- Where the entity is the same on both sides and then Is_Entity_Name (Lhs) and then Is_Entity_Name (Rhs) and then Entity (Lhs) = Entity (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 Error_Msg_NE ("?useless assignment of & to itself", N, Entity (Lhs)); 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); Ent : Entity_Id; begin -- If a label is present analyze it and mark it as referenced if Present (Id) then Analyze (Id); Ent := Entity (Id); 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; -- Otherwise create a label entity else Ent := New_Internal_Entity (E_Block, Current_Scope, Sloc (N), 'B'); Set_Identifier (N, New_Occurrence_Of (Ent, Sloc (N))); end if; Set_Etype (Ent, Standard_Void_Type); Set_Block_Node (Ent, Identifier (N)); New_Scope (Ent); if Present (Decls) then Analyze_Declarations (Decls); Check_Completion; end if; Analyze (Handled_Statement_Sequence (N)); Process_End_Label (Handled_Statement_Sequence (N), 'e', Ent); -- Analyze exception handlers if present. Note that the test for -- HSS being present is an error defence against previous errors. if Present (Handled_Statement_Sequence (N)) and then Present (Exception_Handlers (Handled_Statement_Sequence (N))) then declare S : Entity_Id := Scope (Ent); begin -- Indicate that enclosing scopes contain a block with handlers. -- Only non-generic scopes need to be marked. loop Set_Has_Nested_Block_With_Handler (S); exit when Is_Overloadable (S) or else Ekind (S) = E_Package or else Ekind (S) = E_Generic_Function or else Ekind (S) = E_Generic_Package or else Ekind (S) = E_Generic_Procedure; S := Scope (S); end loop; end; end if; Check_References (Ent); End_Scope; end Analyze_Block_Statement; ---------------------------- -- Analyze_Case_Statement -- ---------------------------- procedure Analyze_Case_Statement (N : Node_Id) is 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 Error_Msg_N ("choice given in case statement is not static", Choice); end Non_Static_Choice_Error; ------------------------ -- Process_Statements -- ------------------------ procedure Process_Statements (Alternative : Node_Id) is begin Unblocked_Exit_Count := Unblocked_Exit_Count + 1; Statements_Analyzed := True; Analyze_Statements (Statements (Alternative)); end Process_Statements; -- Variables local to Analyze_Case_Statement. Exp : Node_Id; Exp_Type : Entity_Id; Exp_Btype : Entity_Id; Case_Table : Choice_Table_Type (1 .. Number_Of_Choices (N)); Last_Choice : Nat; Dont_Care : Boolean; Others_Present : Boolean; -- Start of processing for Analyze_Case_Statement begin Unblocked_Exit_Count := 0; Exp := Expression (N); Analyze_And_Resolve (Exp, Any_Discrete); Check_Unset_Reference (Exp); Exp_Type := Etype (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_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 the 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; 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 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; 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; begin Check_Unreachable_Code (N); Analyze (Label); if Entity (Label) = Any_Id then return; elsif Ekind (Entity (Label)) /= E_Label then Error_Msg_N ("target of goto statement must be a label", Label); return; elsif not Reachable (Entity (Label)) then Error_Msg_N ("target of goto statement is not reachable", Label); return; end if; Label_Scope := Enclosing_Scope (Entity (Label)); 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) 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 deleted 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). 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 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. 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); -- 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 -- 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); -- If condition is False, analyze THEN with expansion off else -- Is_False (Expr_Value (Cond)) Expander_Mode_Save_And_Set (False); Analyze_Statements (Tstm); Expander_Mode_Restore; 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; 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 : 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 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); -- 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); F : List_Id; 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 Analyze (DS); 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; Make_Index (DS, LP); Set_Ekind (Id, E_Loop_Parameter); Set_Etype (Id, Etype (DS)); Set_Is_Known_Valid (Id, True); -- The loop is not a declarative part, so the only entity -- declared "within" must be frozen explicitly. Since the -- type of this entity has already been frozen, this cannot -- generate any freezing actions. F := Freeze_Entity (Id, Sloc (LP)); pragma Assert (F = No_List); -- 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) and then not Inside_A_Generic and then not In_Instance then declare L : constant Node_Id := Low_Bound (DS); H : constant Node_Id := High_Bound (DS); Llo : Uint; Lhi : Uint; LOK : Boolean; Hlo : Uint; Hhi : Uint; HOK : Boolean; begin Determine_Range (L, LOK, Llo, Lhi); Determine_Range (H, HOK, Hlo, Hhi); -- If range of loop is null, issue warning if (LOK and HOK) and then Llo > Hhi then Error_Msg_N ("?loop range is null, loop will not execute", DS); -- 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. elsif Reverse_Present (LP) and then Nkind (H) = N_Integer_Literal and then (Intval (H) = Uint_0 or else Intval (H) = Uint_1) and then Lhi > Hhi then Warn_On_Instance := True; Error_Msg_N ("?loop range may be null", DS); Warn_On_Instance := False; end if; end; end if; end; end if; end; end if; end Analyze_Iteration_Scheme; ------------------- -- Analyze_Label -- ------------------- -- Important note: normally this routine is called from Analyze_Statements -- which does a prescan, to make sure that the Reachable flags are set on -- all labels before encountering a possible goto to one of these labels. -- If expanded code analyzes labels via the normal Sem path, then it must -- ensure that Reachable is set early enough to avoid problems in the case -- of a forward goto. procedure Analyze_Label (N : Node_Id) is Lab : Entity_Id; begin Analyze (Identifier (N)); Lab := Entity (Identifier (N)); -- 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), N); 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 (N)); end if; 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 Id : constant Node_Id := Identifier (N); 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); Generate_Reference (Ent, N, ' '); 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), N); end if; end if; -- Case of no identifier present else Ent := New_Internal_Entity (E_Loop, Current_Scope, Sloc (N), 'L'); Set_Etype (Ent, Standard_Void_Type); Set_Parent (Ent, N); end if; New_Scope (Ent); Analyze_Iteration_Scheme (Iteration_Scheme (N)); Analyze_Statements (Statements (N)); Process_End_Label (N, 'e', Ent); End_Scope; 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; 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_Label (S); end if; Next (S); end loop; -- Perform semantic analysis on all statements S := First (L); while Present (S) loop if Nkind (S) /= N_Label then Analyze (S); end if; Next (S); end loop; -- 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 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_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); exit when No (Nxt) or else not Is_Statement (Nxt); 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 an IF statement, and if so adjust the unblocked exit -- count of the if statement to reflect the fact that this -- branch of the if is indeed blocked by a transfer of control. else P := Parent (N); if Nkind (P) = N_If_Statement then null; elsif Nkind (P) = N_Elsif_Part then P := Parent (P); pragma Assert (Nkind (P) = N_If_Statement); elsif Nkind (P) = N_Case_Statement_Alternative then P := Parent (P); pragma Assert (Nkind (P) = N_Case_Statement); else return; end if; Unblocked_Exit_Count := Unblocked_Exit_Count - 1; end if; end; end if; end Check_Unreachable_Code; end Sem_Ch5;