------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- S E M _ C H 5 -- -- -- -- B o d y -- -- -- -- Copyright (C) 1992-2004 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 Nmake; use Nmake; 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 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 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); procedure Check_Possible_Current_Value_Condition (Cnode : Node_Id); -- Cnode is N_If_Statement, N_Elsif_Part, or N_Iteration_Scheme -- (the latter when a WHILE condition is present). This call checks -- if Condition (Cnode) is of the form ([NOT] var op val), where var -- is a simple object, val is known at compile time, and op is one -- of the six relational operators. If this is the case, and the -- Current_Value field of "var" is not set, then it is set to Cnode. -- See Exp_Util.Set_Current_Value_Condition for further details. ------------------------ -- 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; Ent : Entity_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); -- 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); elsif Ekind (Entity (N)) = 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; -- 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; ------------------------- -- 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 (Opnd) = N_Selected_Component or else Nkind (Opnd) = 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 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 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); 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); Explain_Limited_Type (T1, 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); Check_Unset_Reference (Rhs); -- Remaining steps are skipped if Rhs was syntactically in error if Rhs = Error then return; end if; T2 := Etype (Rhs); if Covers (T1, T2) then null; else Wrong_Type (Rhs, Etype (Lhs)); return; 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 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; -- Ada 2005 (AI-231) if Ada_Version >= Ada_05 and then Nkind (Rhs) = N_Null and then Is_Access_Type (T1) and then not Assignment_OK (Lhs) and then ((Is_Entity_Name (Lhs) and then Can_Never_Be_Null (Entity (Lhs))) or else Can_Never_Be_Null (Etype (Lhs))) then Error_Msg_N ("(Ada 2005) NULL not allowed in null-excluding objects", Lhs); end if; if Is_Scalar_Type (T1) then Apply_Scalar_Range_Check (Rhs, Etype (Lhs)); elsif Is_Array_Type (T1) and then (Nkind (Rhs) /= N_Type_Conversion or else Is_Constrained (Etype (Rhs))) 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); -- ??? 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 (Original_Node (Rhs)) and then Entity (Lhs) = Entity (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 Error_Msg_NE ("?useless assignment of & to itself", N, Entity (Lhs)); 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; -- One more step. Let's see if we have a simple assignment of a -- known at compile time value to a simple variable. If so, we -- can record the value as the current value providing that: -- We still have a simple assignment statement (no expansion -- activity has modified it in some peculiar manner) -- The type is a discrete type -- The assignment is to a named entity -- The value is known at compile time if Nkind (N) /= N_Assignment_Statement or else not Is_Discrete_Type (T1) or else not Is_Entity_Name (Lhs) or else not Compile_Time_Known_Value (Rhs) then return; end if; Ent := Entity (Lhs); -- Capture value if save to do so if Safe_To_Capture_Value (N, Ent) then Set_Current_Value (Ent, Rhs); 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 := Empty; begin -- 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)); 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 Is_Generic_Unit (S); 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 Exp : Node_Id; Exp_Type : Entity_Id; Exp_Btype : Entity_Id; Last_Choice : Nat; Dont_Care : Boolean; Others_Present : Boolean; 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 statment 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)); -- 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_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 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 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); Check_Possible_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 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. -------------------------------------- -- 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); -- 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 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; Check_Controlled_Array_Attribute (DS); 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. 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); 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 -- 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 Error_Msg_N ("?loop range is null, loop will not execute", DS); end if; -- Since we know the range of the loop is null, -- set the appropriate flag to suppress any -- warnings that would otherwise be issued in -- the body of the loop that will not execute. -- We do this even in the generic case, since -- if it is dubious to warn on the null loop -- itself, it is certainly dubious to warn for -- conditions that occur inside it! Set_Is_Null_Loop (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 (H) = N_Integer_Literal and then (Intval (H) = Uint_0 or else Intval (H) = Uint_1) and then Lhi > Hhi then Error_Msg_N ("?loop range may be null", 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 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; -- 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; New_Scope (Ent); Analyze_Iteration_Scheme (Iteration_Scheme (N)); Analyze_Statements (Statements (N)); Process_End_Label (N, 'e', Ent); End_Scope; Kill_Current_Values; 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_Possible_Current_Value_Condition -- -------------------------------------------- procedure Check_Possible_Current_Value_Condition (Cnode : Node_Id) is Cond : Node_Id; begin -- Loop to deal with (ignore for now) any NOT operators present Cond := Condition (Cnode); while Nkind (Cond) = N_Op_Not loop Cond := Right_Opnd (Cond); end loop; -- Check possible relational operator if Nkind (Cond) = N_Op_Eq or else Nkind (Cond) = N_Op_Ne or else Nkind (Cond) = N_Op_Ge or else Nkind (Cond) = N_Op_Le or else Nkind (Cond) = N_Op_Gt or else Nkind (Cond) = N_Op_Lt then if Compile_Time_Known_Value (Right_Opnd (Cond)) and then Nkind (Left_Opnd (Cond)) = N_Identifier then declare Ent : constant Entity_Id := Entity (Left_Opnd (Cond)); begin if Ekind (Ent) = E_Variable or else Ekind (Ent) = E_Constant or else Is_Formal (Ent) or else Ekind (Ent) = E_Loop_Parameter then -- Here we have a case where the Current_Value field -- may need to be set. We set it if it is not already -- set to a compile time expression value. -- Note that this represents a decision that one -- condition blots out another previous one. That's -- certainly right if they occur at the same level. -- If the second one is nested, then the decision is -- neither right nor wrong (it would be equally OK -- to leave the outer one in place, or take the new -- inner one. Really we should record both, but our -- data structures are not that elaborate. if Nkind (Current_Value (Ent)) not in N_Subexpr then Set_Current_Value (Ent, Cnode); end if; end if; end; end if; end if; end Check_Possible_Current_Value_Condition; ---------------------------- -- 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); -- 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 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;