1 ------------------------------------------------------------------------------
3 -- GNAT COMPILER COMPONENTS --
9 -- Copyright (C) 1992-2004 Free Software Foundation, Inc. --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 2, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING. If not, write --
19 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
20 -- MA 02111-1307, USA. --
22 -- GNAT was originally developed by the GNAT team at New York University. --
23 -- Extensive contributions were provided by Ada Core Technologies Inc. --
25 ------------------------------------------------------------------------------
27 with Atree; use Atree;
28 with Checks; use Checks;
29 with Einfo; use Einfo;
30 with Errout; use Errout;
31 with Expander; use Expander;
32 with Exp_Util; use Exp_Util;
33 with Freeze; use Freeze;
34 with Lib.Xref; use Lib.Xref;
35 with Nlists; use Nlists;
36 with Nmake; use Nmake;
39 with Sem_Case; use Sem_Case;
40 with Sem_Ch3; use Sem_Ch3;
41 with Sem_Ch8; use Sem_Ch8;
42 with Sem_Disp; use Sem_Disp;
43 with Sem_Eval; use Sem_Eval;
44 with Sem_Res; use Sem_Res;
45 with Sem_Type; use Sem_Type;
46 with Sem_Util; use Sem_Util;
47 with Sem_Warn; use Sem_Warn;
48 with Stand; use Stand;
49 with Sinfo; use Sinfo;
50 with Targparm; use Targparm;
51 with Tbuild; use Tbuild;
52 with Uintp; use Uintp;
54 package body Sem_Ch5 is
56 Unblocked_Exit_Count : Nat := 0;
57 -- This variable is used when processing if statements or case
58 -- statements, it counts the number of branches of the conditional
59 -- that are not blocked by unconditional transfer instructions. At
60 -- the end of processing, if the count is zero, it means that control
61 -- cannot fall through the conditional statement. This is used for
62 -- the generation of warning messages. This variable is recursively
63 -- saved on entry to processing an if or case, and restored on exit.
65 -----------------------
66 -- Local Subprograms --
67 -----------------------
69 procedure Analyze_Iteration_Scheme (N : Node_Id);
71 procedure Check_Possible_Current_Value_Condition (Cnode : Node_Id);
72 -- Cnode is N_If_Statement, N_Elsif_Part, or N_Iteration_Scheme
73 -- (the latter when a WHILE condition is present). This call checks
74 -- if Condition (Cnode) is of the form ([NOT] var op val), where var
75 -- is a simple object, val is known at compile time, and op is one
76 -- of the six relational operators. If this is the case, and the
77 -- Current_Value field of "var" is not set, then it is set to Cnode.
78 -- See Exp_Util.Set_Current_Value_Condition for further details.
80 ------------------------
81 -- Analyze_Assignment --
82 ------------------------
84 procedure Analyze_Assignment (N : Node_Id) is
85 Lhs : constant Node_Id := Name (N);
86 Rhs : constant Node_Id := Expression (N);
92 procedure Diagnose_Non_Variable_Lhs (N : Node_Id);
93 -- N is the node for the left hand side of an assignment, and it
94 -- is not a variable. This routine issues an appropriate diagnostic.
96 procedure Set_Assignment_Type
98 Opnd_Type : in out Entity_Id);
99 -- Opnd is either the Lhs or Rhs of the assignment, and Opnd_Type
100 -- is the nominal subtype. This procedure is used to deal with cases
101 -- where the nominal subtype must be replaced by the actual subtype.
103 -------------------------------
104 -- Diagnose_Non_Variable_Lhs --
105 -------------------------------
107 procedure Diagnose_Non_Variable_Lhs (N : Node_Id) is
109 -- Not worth posting another error if left hand side already
110 -- flagged as being illegal in some respect
112 if Error_Posted (N) then
115 -- Some special bad cases of entity names
117 elsif Is_Entity_Name (N) then
118 if Ekind (Entity (N)) = E_In_Parameter then
120 ("assignment to IN mode parameter not allowed", N);
122 -- Private declarations in a protected object are turned into
123 -- constants when compiling a protected function.
125 elsif Present (Scope (Entity (N)))
126 and then Is_Protected_Type (Scope (Entity (N)))
128 (Ekind (Current_Scope) = E_Function
130 Ekind (Enclosing_Dynamic_Scope (Current_Scope)) = E_Function)
133 ("protected function cannot modify protected object", N);
135 elsif Ekind (Entity (N)) = E_Loop_Parameter then
137 ("assignment to loop parameter not allowed", N);
141 ("left hand side of assignment must be a variable", N);
144 -- For indexed components or selected components, test prefix
146 elsif Nkind (N) = N_Indexed_Component then
147 Diagnose_Non_Variable_Lhs (Prefix (N));
149 -- Another special case for assignment to discriminant.
151 elsif Nkind (N) = N_Selected_Component then
152 if Present (Entity (Selector_Name (N)))
153 and then Ekind (Entity (Selector_Name (N))) = E_Discriminant
156 ("assignment to discriminant not allowed", N);
158 Diagnose_Non_Variable_Lhs (Prefix (N));
162 -- If we fall through, we have no special message to issue!
164 Error_Msg_N ("left hand side of assignment must be a variable", N);
166 end Diagnose_Non_Variable_Lhs;
168 -------------------------
169 -- Set_Assignment_Type --
170 -------------------------
172 procedure Set_Assignment_Type
174 Opnd_Type : in out Entity_Id)
177 Require_Entity (Opnd);
179 -- If the assignment operand is an in-out or out parameter, then we
180 -- get the actual subtype (needed for the unconstrained case).
181 -- If the operand is the actual in an entry declaration, then within
182 -- the accept statement it is replaced with a local renaming, which
183 -- may also have an actual subtype.
185 if Is_Entity_Name (Opnd)
186 and then (Ekind (Entity (Opnd)) = E_Out_Parameter
187 or else Ekind (Entity (Opnd)) =
189 or else Ekind (Entity (Opnd)) =
190 E_Generic_In_Out_Parameter
192 (Ekind (Entity (Opnd)) = E_Variable
193 and then Nkind (Parent (Entity (Opnd))) =
194 N_Object_Renaming_Declaration
195 and then Nkind (Parent (Parent (Entity (Opnd)))) =
198 Opnd_Type := Get_Actual_Subtype (Opnd);
200 -- If assignment operand is a component reference, then we get the
201 -- actual subtype of the component for the unconstrained case.
204 (Nkind (Opnd) = N_Selected_Component
205 or else Nkind (Opnd) = N_Explicit_Dereference)
206 and then not Is_Unchecked_Union (Opnd_Type)
208 Decl := Build_Actual_Subtype_Of_Component (Opnd_Type, Opnd);
210 if Present (Decl) then
211 Insert_Action (N, Decl);
212 Mark_Rewrite_Insertion (Decl);
214 Opnd_Type := Defining_Identifier (Decl);
215 Set_Etype (Opnd, Opnd_Type);
216 Freeze_Itype (Opnd_Type, N);
218 elsif Is_Constrained (Etype (Opnd)) then
219 Opnd_Type := Etype (Opnd);
222 -- For slice, use the constrained subtype created for the slice
224 elsif Nkind (Opnd) = N_Slice then
225 Opnd_Type := Etype (Opnd);
227 end Set_Assignment_Type;
229 -- Start of processing for Analyze_Assignment
236 -- In the most general case, both Lhs and Rhs can be overloaded, and we
237 -- must compute the intersection of the possible types on each side.
239 if Is_Overloaded (Lhs) then
246 Get_First_Interp (Lhs, I, It);
248 while Present (It.Typ) loop
249 if Has_Compatible_Type (Rhs, It.Typ) then
250 if T1 /= Any_Type then
252 -- An explicit dereference is overloaded if the prefix
253 -- is. Try to remove the ambiguity on the prefix, the
254 -- error will be posted there if the ambiguity is real.
256 if Nkind (Lhs) = N_Explicit_Dereference then
259 PI1 : Interp_Index := 0;
265 Get_First_Interp (Prefix (Lhs), PI, PIt);
267 while Present (PIt.Typ) loop
268 if Is_Access_Type (PIt.Typ)
269 and then Has_Compatible_Type
270 (Rhs, Designated_Type (PIt.Typ))
274 Disambiguate (Prefix (Lhs),
277 if PIt = No_Interp then
279 ("ambiguous left-hand side"
280 & " in assignment", Lhs);
283 Resolve (Prefix (Lhs), PIt.Typ);
293 Get_Next_Interp (PI, PIt);
299 ("ambiguous left-hand side in assignment", Lhs);
307 Get_Next_Interp (I, It);
311 if T1 = Any_Type then
313 ("no valid types for left-hand side for assignment", Lhs);
320 if not Is_Variable (Lhs) then
321 Diagnose_Non_Variable_Lhs (Lhs);
324 elsif Is_Limited_Type (T1)
325 and then not Assignment_OK (Lhs)
326 and then not Assignment_OK (Original_Node (Lhs))
329 ("left hand of assignment must not be limited type", Lhs);
330 Explain_Limited_Type (T1, Lhs);
334 -- Resolution may have updated the subtype, in case the left-hand
335 -- side is a private protected component. Use the correct subtype
336 -- to avoid scoping issues in the back-end.
339 Set_Assignment_Type (Lhs, T1);
342 Check_Unset_Reference (Rhs);
344 -- Remaining steps are skipped if Rhs was syntactically in error
352 if Covers (T1, T2) then
355 Wrong_Type (Rhs, Etype (Lhs));
359 Set_Assignment_Type (Rhs, T2);
361 if Total_Errors_Detected /= 0 then
371 if T1 = Any_Type or else T2 = Any_Type then
375 if (Is_Class_Wide_Type (T2) or else Is_Dynamically_Tagged (Rhs))
376 and then not Is_Class_Wide_Type (T1)
378 Error_Msg_N ("dynamically tagged expression not allowed!", Rhs);
380 elsif Is_Class_Wide_Type (T1)
381 and then not Is_Class_Wide_Type (T2)
382 and then not Is_Tag_Indeterminate (Rhs)
383 and then not Is_Dynamically_Tagged (Rhs)
385 Error_Msg_N ("dynamically tagged expression required!", Rhs);
388 -- Tag propagation is done only in semantics mode only. If expansion
389 -- is on, the rhs tag indeterminate function call has been expanded
390 -- and tag propagation would have happened too late, so the
391 -- propagation take place in expand_call instead.
393 if not Expander_Active
394 and then Is_Class_Wide_Type (T1)
395 and then Is_Tag_Indeterminate (Rhs)
397 Propagate_Tag (Lhs, Rhs);
402 if Ada_Version >= Ada_05
403 and then Nkind (Rhs) = N_Null
404 and then Is_Access_Type (T1)
405 and then not Assignment_OK (Lhs)
406 and then ((Is_Entity_Name (Lhs)
407 and then Can_Never_Be_Null (Entity (Lhs)))
408 or else Can_Never_Be_Null (Etype (Lhs)))
411 ("(Ada 2005) NULL not allowed in null-excluding objects", Lhs);
414 if Is_Scalar_Type (T1) then
415 Apply_Scalar_Range_Check (Rhs, Etype (Lhs));
417 elsif Is_Array_Type (T1)
419 (Nkind (Rhs) /= N_Type_Conversion
420 or else Is_Constrained (Etype (Rhs)))
422 -- Assignment verifies that the length of the Lsh and Rhs are equal,
423 -- but of course the indices do not have to match. If the right-hand
424 -- side is a type conversion to an unconstrained type, a length check
425 -- is performed on the expression itself during expansion. In rare
426 -- cases, the redundant length check is computed on an index type
427 -- with a different representation, triggering incorrect code in
430 Apply_Length_Check (Rhs, Etype (Lhs));
433 -- Discriminant checks are applied in the course of expansion
438 -- Note: modifications of the Lhs may only be recorded after
439 -- checks have been applied.
441 Note_Possible_Modification (Lhs);
443 -- ??? a real accessibility check is needed when ???
445 -- Post warning for useless assignment
447 if Warn_On_Redundant_Constructs
449 -- We only warn for source constructs
451 and then Comes_From_Source (N)
453 -- Where the entity is the same on both sides
455 and then Is_Entity_Name (Lhs)
456 and then Is_Entity_Name (Original_Node (Rhs))
457 and then Entity (Lhs) = Entity (Original_Node (Rhs))
459 -- But exclude the case where the right side was an operation
460 -- that got rewritten (e.g. JUNK + K, where K was known to be
461 -- zero). We don't want to warn in such a case, since it is
462 -- reasonable to write such expressions especially when K is
463 -- defined symbolically in some other package.
465 and then Nkind (Original_Node (Rhs)) not in N_Op
468 ("?useless assignment of & to itself", N, Entity (Lhs));
471 -- Check for non-allowed composite assignment
473 if not Support_Composite_Assign_On_Target
474 and then (Is_Array_Type (T1) or else Is_Record_Type (T1))
475 and then (not Has_Size_Clause (T1) or else Esize (T1) > 64)
477 Error_Msg_CRT ("composite assignment", N);
480 -- One more step. Let's see if we have a simple assignment of a
481 -- known at compile time value to a simple variable. If so, we
482 -- can record the value as the current value providing that:
484 -- We still have a simple assignment statement (no expansion
485 -- activity has modified it in some peculiar manner)
487 -- The type is a discrete type
489 -- The assignment is to a named entity
491 -- The value is known at compile time
493 if Nkind (N) /= N_Assignment_Statement
494 or else not Is_Discrete_Type (T1)
495 or else not Is_Entity_Name (Lhs)
496 or else not Compile_Time_Known_Value (Rhs)
503 -- Capture value if save to do so
505 if Safe_To_Capture_Value (N, Ent) then
506 Set_Current_Value (Ent, Rhs);
508 end Analyze_Assignment;
510 -----------------------------
511 -- Analyze_Block_Statement --
512 -----------------------------
514 procedure Analyze_Block_Statement (N : Node_Id) is
515 Decls : constant List_Id := Declarations (N);
516 Id : constant Node_Id := Identifier (N);
517 Ent : Entity_Id := Empty;
520 -- If a label is present analyze it and mark it as referenced
526 -- An error defense. If we have an identifier, but no entity, then
527 -- something is wrong. If we have previous errors, then just remove
528 -- the identifier and continue, otherwise raise an exception.
531 if Total_Errors_Detected /= 0 then
532 Set_Identifier (N, Empty);
538 Set_Ekind (Ent, E_Block);
539 Generate_Reference (Ent, N, ' ');
540 Generate_Definition (Ent);
542 if Nkind (Parent (Ent)) = N_Implicit_Label_Declaration then
543 Set_Label_Construct (Parent (Ent), N);
548 -- If no entity set, create a label entity
551 Ent := New_Internal_Entity (E_Block, Current_Scope, Sloc (N), 'B');
552 Set_Identifier (N, New_Occurrence_Of (Ent, Sloc (N)));
556 Set_Etype (Ent, Standard_Void_Type);
557 Set_Block_Node (Ent, Identifier (N));
560 if Present (Decls) then
561 Analyze_Declarations (Decls);
565 Analyze (Handled_Statement_Sequence (N));
566 Process_End_Label (Handled_Statement_Sequence (N), 'e', Ent);
568 -- Analyze exception handlers if present. Note that the test for
569 -- HSS being present is an error defence against previous errors.
571 if Present (Handled_Statement_Sequence (N))
572 and then Present (Exception_Handlers (Handled_Statement_Sequence (N)))
575 S : Entity_Id := Scope (Ent);
578 -- Indicate that enclosing scopes contain a block with handlers.
579 -- Only non-generic scopes need to be marked.
582 Set_Has_Nested_Block_With_Handler (S);
583 exit when Is_Overloadable (S)
584 or else Ekind (S) = E_Package
585 or else Is_Generic_Unit (S);
591 Check_References (Ent);
593 end Analyze_Block_Statement;
595 ----------------------------
596 -- Analyze_Case_Statement --
597 ----------------------------
599 procedure Analyze_Case_Statement (N : Node_Id) is
601 Exp_Type : Entity_Id;
602 Exp_Btype : Entity_Id;
605 Others_Present : Boolean;
607 Statements_Analyzed : Boolean := False;
608 -- Set True if at least some statement sequences get analyzed.
609 -- If False on exit, means we had a serious error that prevented
610 -- full analysis of the case statement, and as a result it is not
611 -- a good idea to output warning messages about unreachable code.
613 Save_Unblocked_Exit_Count : constant Nat := Unblocked_Exit_Count;
614 -- Recursively save value of this global, will be restored on exit
616 procedure Non_Static_Choice_Error (Choice : Node_Id);
617 -- Error routine invoked by the generic instantiation below when
618 -- the case statment has a non static choice.
620 procedure Process_Statements (Alternative : Node_Id);
621 -- Analyzes all the statements associated to a case alternative.
622 -- Needed by the generic instantiation below.
624 package Case_Choices_Processing is new
625 Generic_Choices_Processing
626 (Get_Alternatives => Alternatives,
627 Get_Choices => Discrete_Choices,
628 Process_Empty_Choice => No_OP,
629 Process_Non_Static_Choice => Non_Static_Choice_Error,
630 Process_Associated_Node => Process_Statements);
631 use Case_Choices_Processing;
632 -- Instantiation of the generic choice processing package
634 -----------------------------
635 -- Non_Static_Choice_Error --
636 -----------------------------
638 procedure Non_Static_Choice_Error (Choice : Node_Id) is
641 ("choice given in case statement is not static!", Choice);
642 end Non_Static_Choice_Error;
644 ------------------------
645 -- Process_Statements --
646 ------------------------
648 procedure Process_Statements (Alternative : Node_Id) is
649 Choices : constant List_Id := Discrete_Choices (Alternative);
653 Unblocked_Exit_Count := Unblocked_Exit_Count + 1;
654 Statements_Analyzed := True;
656 -- An interesting optimization. If the case statement expression
657 -- is a simple entity, then we can set the current value within
658 -- an alternative if the alternative has one possible value.
662 -- when 2 | 3 => beta
663 -- when others => gamma
665 -- Here we know that N is initially 1 within alpha, but for beta
666 -- and gamma, we do not know anything more about the initial value.
668 if Is_Entity_Name (Exp) then
671 if Ekind (Ent) = E_Variable
673 Ekind (Ent) = E_In_Out_Parameter
675 Ekind (Ent) = E_Out_Parameter
677 if List_Length (Choices) = 1
678 and then Nkind (First (Choices)) in N_Subexpr
679 and then Compile_Time_Known_Value (First (Choices))
681 Set_Current_Value (Entity (Exp), First (Choices));
684 Analyze_Statements (Statements (Alternative));
686 -- After analyzing the case, set the current value to empty
687 -- since we won't know what it is for the next alternative
688 -- (unless reset by this same circuit), or after the case.
690 Set_Current_Value (Entity (Exp), Empty);
695 -- Case where expression is not an entity name of a variable
697 Analyze_Statements (Statements (Alternative));
698 end Process_Statements;
700 -- Table to record choices. Put after subprograms since we make
701 -- a call to Number_Of_Choices to get the right number of entries.
703 Case_Table : Choice_Table_Type (1 .. Number_Of_Choices (N));
705 -- Start of processing for Analyze_Case_Statement
708 Unblocked_Exit_Count := 0;
709 Exp := Expression (N);
710 Analyze_And_Resolve (Exp, Any_Discrete);
711 Check_Unset_Reference (Exp);
712 Exp_Type := Etype (Exp);
713 Exp_Btype := Base_Type (Exp_Type);
715 -- The expression must be of a discrete type which must be determinable
716 -- independently of the context in which the expression occurs, but
717 -- using the fact that the expression must be of a discrete type.
718 -- Moreover, the type this expression must not be a character literal
719 -- (which is always ambiguous) or, for Ada-83, a generic formal type.
721 -- If error already reported by Resolve, nothing more to do
723 if Exp_Btype = Any_Discrete
724 or else Exp_Btype = Any_Type
728 elsif Exp_Btype = Any_Character then
730 ("character literal as case expression is ambiguous", Exp);
733 elsif Ada_Version = Ada_83
734 and then (Is_Generic_Type (Exp_Btype)
735 or else Is_Generic_Type (Root_Type (Exp_Btype)))
738 ("(Ada 83) case expression cannot be of a generic type", Exp);
742 -- If the case expression is a formal object of mode in out, then
743 -- treat it as having a nonstatic subtype by forcing use of the base
744 -- type (which has to get passed to Check_Case_Choices below). Also
745 -- use base type when the case expression is parenthesized.
747 if Paren_Count (Exp) > 0
748 or else (Is_Entity_Name (Exp)
749 and then Ekind (Entity (Exp)) = E_Generic_In_Out_Parameter)
751 Exp_Type := Exp_Btype;
754 -- Call instantiated Analyze_Choices which does the rest of the work
757 (N, Exp_Type, Case_Table, Last_Choice, Dont_Care, Others_Present);
759 if Exp_Type = Universal_Integer and then not Others_Present then
760 Error_Msg_N ("case on universal integer requires OTHERS choice", Exp);
763 -- If all our exits were blocked by unconditional transfers of control,
764 -- then the entire CASE statement acts as an unconditional transfer of
765 -- control, so treat it like one, and check unreachable code. Skip this
766 -- test if we had serious errors preventing any statement analysis.
768 if Unblocked_Exit_Count = 0 and then Statements_Analyzed then
769 Unblocked_Exit_Count := Save_Unblocked_Exit_Count;
770 Check_Unreachable_Code (N);
772 Unblocked_Exit_Count := Save_Unblocked_Exit_Count;
775 if not Expander_Active
776 and then Compile_Time_Known_Value (Expression (N))
777 and then Serious_Errors_Detected = 0
780 Chosen : constant Node_Id := Find_Static_Alternative (N);
784 Alt := First (Alternatives (N));
786 while Present (Alt) loop
787 if Alt /= Chosen then
788 Remove_Warning_Messages (Statements (Alt));
795 end Analyze_Case_Statement;
797 ----------------------------
798 -- Analyze_Exit_Statement --
799 ----------------------------
801 -- If the exit includes a name, it must be the name of a currently open
802 -- loop. Otherwise there must be an innermost open loop on the stack,
803 -- to which the statement implicitly refers.
805 procedure Analyze_Exit_Statement (N : Node_Id) is
806 Target : constant Node_Id := Name (N);
807 Cond : constant Node_Id := Condition (N);
808 Scope_Id : Entity_Id;
814 Check_Unreachable_Code (N);
817 if Present (Target) then
819 U_Name := Entity (Target);
821 if not In_Open_Scopes (U_Name) or else Ekind (U_Name) /= E_Loop then
822 Error_Msg_N ("invalid loop name in exit statement", N);
825 Set_Has_Exit (U_Name);
832 for J in reverse 0 .. Scope_Stack.Last loop
833 Scope_Id := Scope_Stack.Table (J).Entity;
834 Kind := Ekind (Scope_Id);
837 and then (No (Target) or else Scope_Id = U_Name) then
838 Set_Has_Exit (Scope_Id);
841 elsif Kind = E_Block or else Kind = E_Loop then
846 ("cannot exit from program unit or accept statement", N);
851 -- Verify that if present the condition is a Boolean expression
853 if Present (Cond) then
854 Analyze_And_Resolve (Cond, Any_Boolean);
855 Check_Unset_Reference (Cond);
857 end Analyze_Exit_Statement;
859 ----------------------------
860 -- Analyze_Goto_Statement --
861 ----------------------------
863 procedure Analyze_Goto_Statement (N : Node_Id) is
864 Label : constant Node_Id := Name (N);
865 Scope_Id : Entity_Id;
866 Label_Scope : Entity_Id;
869 Check_Unreachable_Code (N);
873 if Entity (Label) = Any_Id then
876 elsif Ekind (Entity (Label)) /= E_Label then
877 Error_Msg_N ("target of goto statement must be a label", Label);
880 elsif not Reachable (Entity (Label)) then
881 Error_Msg_N ("target of goto statement is not reachable", Label);
885 Label_Scope := Enclosing_Scope (Entity (Label));
887 for J in reverse 0 .. Scope_Stack.Last loop
888 Scope_Id := Scope_Stack.Table (J).Entity;
890 if Label_Scope = Scope_Id
891 or else (Ekind (Scope_Id) /= E_Block
892 and then Ekind (Scope_Id) /= E_Loop)
894 if Scope_Id /= Label_Scope then
896 ("cannot exit from program unit or accept statement", N);
904 end Analyze_Goto_Statement;
906 --------------------------
907 -- Analyze_If_Statement --
908 --------------------------
910 -- A special complication arises in the analysis of if statements.
912 -- The expander has circuitry to completely delete code that it
913 -- can tell will not be executed (as a result of compile time known
914 -- conditions). In the analyzer, we ensure that code that will be
915 -- deleted in this manner is analyzed but not expanded. This is
916 -- obviously more efficient, but more significantly, difficulties
917 -- arise if code is expanded and then eliminated (e.g. exception
918 -- table entries disappear). Similarly, itypes generated in deleted
919 -- code must be frozen from start, because the nodes on which they
920 -- depend will not be available at the freeze point.
922 procedure Analyze_If_Statement (N : Node_Id) is
925 Save_Unblocked_Exit_Count : constant Nat := Unblocked_Exit_Count;
926 -- Recursively save value of this global, will be restored on exit
928 Save_In_Deleted_Code : Boolean;
930 Del : Boolean := False;
931 -- This flag gets set True if a True condition has been found,
932 -- which means that remaining ELSE/ELSIF parts are deleted.
934 procedure Analyze_Cond_Then (Cnode : Node_Id);
935 -- This is applied to either the N_If_Statement node itself or
936 -- to an N_Elsif_Part node. It deals with analyzing the condition
937 -- and the THEN statements associated with it.
939 -----------------------
940 -- Analyze_Cond_Then --
941 -----------------------
943 procedure Analyze_Cond_Then (Cnode : Node_Id) is
944 Cond : constant Node_Id := Condition (Cnode);
945 Tstm : constant List_Id := Then_Statements (Cnode);
948 Unblocked_Exit_Count := Unblocked_Exit_Count + 1;
949 Analyze_And_Resolve (Cond, Any_Boolean);
950 Check_Unset_Reference (Cond);
951 Check_Possible_Current_Value_Condition (Cnode);
953 -- If already deleting, then just analyze then statements
956 Analyze_Statements (Tstm);
958 -- Compile time known value, not deleting yet
960 elsif Compile_Time_Known_Value (Cond) then
961 Save_In_Deleted_Code := In_Deleted_Code;
963 -- If condition is True, then analyze the THEN statements
964 -- and set no expansion for ELSE and ELSIF parts.
966 if Is_True (Expr_Value (Cond)) then
967 Analyze_Statements (Tstm);
969 Expander_Mode_Save_And_Set (False);
970 In_Deleted_Code := True;
972 -- If condition is False, analyze THEN with expansion off
974 else -- Is_False (Expr_Value (Cond))
975 Expander_Mode_Save_And_Set (False);
976 In_Deleted_Code := True;
977 Analyze_Statements (Tstm);
978 Expander_Mode_Restore;
979 In_Deleted_Code := Save_In_Deleted_Code;
982 -- Not known at compile time, not deleting, normal analysis
985 Analyze_Statements (Tstm);
987 end Analyze_Cond_Then;
989 -- Start of Analyze_If_Statement
992 -- Initialize exit count for else statements. If there is no else
993 -- part, this count will stay non-zero reflecting the fact that the
994 -- uncovered else case is an unblocked exit.
996 Unblocked_Exit_Count := 1;
997 Analyze_Cond_Then (N);
999 -- Now to analyze the elsif parts if any are present
1001 if Present (Elsif_Parts (N)) then
1002 E := First (Elsif_Parts (N));
1003 while Present (E) loop
1004 Analyze_Cond_Then (E);
1009 if Present (Else_Statements (N)) then
1010 Analyze_Statements (Else_Statements (N));
1013 -- If all our exits were blocked by unconditional transfers of control,
1014 -- then the entire IF statement acts as an unconditional transfer of
1015 -- control, so treat it like one, and check unreachable code.
1017 if Unblocked_Exit_Count = 0 then
1018 Unblocked_Exit_Count := Save_Unblocked_Exit_Count;
1019 Check_Unreachable_Code (N);
1021 Unblocked_Exit_Count := Save_Unblocked_Exit_Count;
1025 Expander_Mode_Restore;
1026 In_Deleted_Code := Save_In_Deleted_Code;
1029 if not Expander_Active
1030 and then Compile_Time_Known_Value (Condition (N))
1031 and then Serious_Errors_Detected = 0
1033 if Is_True (Expr_Value (Condition (N))) then
1034 Remove_Warning_Messages (Else_Statements (N));
1036 if Present (Elsif_Parts (N)) then
1037 E := First (Elsif_Parts (N));
1039 while Present (E) loop
1040 Remove_Warning_Messages (Then_Statements (E));
1046 Remove_Warning_Messages (Then_Statements (N));
1049 end Analyze_If_Statement;
1051 ----------------------------------------
1052 -- Analyze_Implicit_Label_Declaration --
1053 ----------------------------------------
1055 -- An implicit label declaration is generated in the innermost
1056 -- enclosing declarative part. This is done for labels as well as
1057 -- block and loop names.
1059 -- Note: any changes in this routine may need to be reflected in
1060 -- Analyze_Label_Entity.
1062 procedure Analyze_Implicit_Label_Declaration (N : Node_Id) is
1063 Id : constant Node_Id := Defining_Identifier (N);
1066 Set_Ekind (Id, E_Label);
1067 Set_Etype (Id, Standard_Void_Type);
1068 Set_Enclosing_Scope (Id, Current_Scope);
1069 end Analyze_Implicit_Label_Declaration;
1071 ------------------------------
1072 -- Analyze_Iteration_Scheme --
1073 ------------------------------
1075 procedure Analyze_Iteration_Scheme (N : Node_Id) is
1076 procedure Check_Controlled_Array_Attribute (DS : Node_Id);
1077 -- If the bounds are given by a 'Range reference on a function call
1078 -- that returns a controlled array, introduce an explicit declaration
1079 -- to capture the bounds, so that the function result can be finalized
1080 -- in timely fashion.
1082 --------------------------------------
1083 -- Check_Controlled_Array_Attribute --
1084 --------------------------------------
1086 procedure Check_Controlled_Array_Attribute (DS : Node_Id) is
1088 if Nkind (DS) = N_Attribute_Reference
1089 and then Is_Entity_Name (Prefix (DS))
1090 and then Ekind (Entity (Prefix (DS))) = E_Function
1091 and then Is_Array_Type (Etype (Entity (Prefix (DS))))
1094 Component_Type (Etype (Entity (Prefix (DS)))))
1095 and then Expander_Active
1098 Loc : constant Source_Ptr := Sloc (N);
1099 Arr : constant Entity_Id :=
1100 Etype (Entity (Prefix (DS)));
1101 Indx : constant Entity_Id :=
1102 Base_Type (Etype (First_Index (Arr)));
1103 Subt : constant Entity_Id :=
1104 Make_Defining_Identifier
1105 (Loc, New_Internal_Name ('S'));
1110 Make_Subtype_Declaration (Loc,
1111 Defining_Identifier => Subt,
1112 Subtype_Indication =>
1113 Make_Subtype_Indication (Loc,
1114 Subtype_Mark => New_Reference_To (Indx, Loc),
1116 Make_Range_Constraint (Loc,
1117 Relocate_Node (DS))));
1118 Insert_Before (Parent (N), Decl);
1122 Make_Attribute_Reference (Loc,
1123 Prefix => New_Reference_To (Subt, Loc),
1124 Attribute_Name => Attribute_Name (DS)));
1128 end Check_Controlled_Array_Attribute;
1130 -- Start of processing for Analyze_Iteration_Scheme
1133 -- For an infinite loop, there is no iteration scheme
1140 Cond : constant Node_Id := Condition (N);
1143 -- For WHILE loop, verify that the condition is a Boolean
1144 -- expression and resolve and check it.
1146 if Present (Cond) then
1147 Analyze_And_Resolve (Cond, Any_Boolean);
1148 Check_Unset_Reference (Cond);
1150 -- Else we have a FOR loop
1154 LP : constant Node_Id := Loop_Parameter_Specification (N);
1155 Id : constant Entity_Id := Defining_Identifier (LP);
1156 DS : constant Node_Id := Discrete_Subtype_Definition (LP);
1161 -- We always consider the loop variable to be referenced,
1162 -- since the loop may be used just for counting purposes.
1164 Generate_Reference (Id, N, ' ');
1166 -- Check for case of loop variable hiding a local
1167 -- variable (used later on to give a nice warning
1168 -- if the hidden variable is never assigned).
1171 H : constant Entity_Id := Homonym (Id);
1174 and then Enclosing_Dynamic_Scope (H) =
1175 Enclosing_Dynamic_Scope (Id)
1176 and then Ekind (H) = E_Variable
1177 and then Is_Discrete_Type (Etype (H))
1179 Set_Hiding_Loop_Variable (H, Id);
1183 -- Now analyze the subtype definition
1191 -- The subtype indication may denote the completion
1192 -- of an incomplete type declaration.
1194 if Is_Entity_Name (DS)
1195 and then Present (Entity (DS))
1196 and then Is_Type (Entity (DS))
1197 and then Ekind (Entity (DS)) = E_Incomplete_Type
1199 Set_Entity (DS, Get_Full_View (Entity (DS)));
1200 Set_Etype (DS, Entity (DS));
1203 if not Is_Discrete_Type (Etype (DS)) then
1204 Wrong_Type (DS, Any_Discrete);
1205 Set_Etype (DS, Any_Type);
1208 Check_Controlled_Array_Attribute (DS);
1209 Make_Index (DS, LP);
1211 Set_Ekind (Id, E_Loop_Parameter);
1212 Set_Etype (Id, Etype (DS));
1213 Set_Is_Known_Valid (Id, True);
1215 -- The loop is not a declarative part, so the only entity
1216 -- declared "within" must be frozen explicitly.
1219 Flist : constant List_Id := Freeze_Entity (Id, Sloc (N));
1221 if Is_Non_Empty_List (Flist) then
1222 Insert_Actions (N, Flist);
1226 -- Check for null or possibly null range and issue warning.
1227 -- We suppress such messages in generic templates and
1228 -- instances, because in practice they tend to be dubious
1231 if Nkind (DS) = N_Range
1232 and then Comes_From_Source (N)
1235 L : constant Node_Id := Low_Bound (DS);
1236 H : constant Node_Id := High_Bound (DS);
1246 Determine_Range (L, LOK, Llo, Lhi);
1247 Determine_Range (H, HOK, Hlo, Hhi);
1249 -- If range of loop is null, issue warning
1251 if (LOK and HOK) and then Llo > Hhi then
1253 -- Suppress the warning if inside a generic
1254 -- template or instance, since in practice
1255 -- they tend to be dubious in these cases since
1256 -- they can result from intended parametrization.
1258 if not Inside_A_Generic
1259 and then not In_Instance
1262 ("?loop range is null, loop will not execute",
1266 -- Since we know the range of the loop is null,
1267 -- set the appropriate flag to suppress any
1268 -- warnings that would otherwise be issued in
1269 -- the body of the loop that will not execute.
1270 -- We do this even in the generic case, since
1271 -- if it is dubious to warn on the null loop
1272 -- itself, it is certainly dubious to warn for
1273 -- conditions that occur inside it!
1275 Set_Is_Null_Loop (Parent (N));
1277 -- The other case for a warning is a reverse loop
1278 -- where the upper bound is the integer literal
1279 -- zero or one, and the lower bound can be positive.
1281 -- For example, we have
1283 -- for J in reverse N .. 1 loop
1285 -- In practice, this is very likely to be a case
1286 -- of reversing the bounds incorrectly in the range.
1288 elsif Reverse_Present (LP)
1289 and then Nkind (H) = N_Integer_Literal
1290 and then (Intval (H) = Uint_0
1292 Intval (H) = Uint_1)
1295 Error_Msg_N ("?loop range may be null", DS);
1303 end Analyze_Iteration_Scheme;
1309 -- Note: the semantic work required for analyzing labels (setting them as
1310 -- reachable) was done in a prepass through the statements in the block,
1311 -- so that forward gotos would be properly handled. See Analyze_Statements
1312 -- for further details. The only processing required here is to deal with
1313 -- optimizations that depend on an assumption of sequential control flow,
1314 -- since of course the occurrence of a label breaks this assumption.
1316 procedure Analyze_Label (N : Node_Id) is
1317 pragma Warnings (Off, N);
1319 Kill_Current_Values;
1322 --------------------------
1323 -- Analyze_Label_Entity --
1324 --------------------------
1326 procedure Analyze_Label_Entity (E : Entity_Id) is
1328 Set_Ekind (E, E_Label);
1329 Set_Etype (E, Standard_Void_Type);
1330 Set_Enclosing_Scope (E, Current_Scope);
1331 Set_Reachable (E, True);
1332 end Analyze_Label_Entity;
1334 ----------------------------
1335 -- Analyze_Loop_Statement --
1336 ----------------------------
1338 procedure Analyze_Loop_Statement (N : Node_Id) is
1339 Id : constant Node_Id := Identifier (N);
1343 if Present (Id) then
1345 -- Make name visible, e.g. for use in exit statements. Loop
1346 -- labels are always considered to be referenced.
1350 Generate_Reference (Ent, N, ' ');
1351 Generate_Definition (Ent);
1353 -- If we found a label, mark its type. If not, ignore it, since it
1354 -- means we have a conflicting declaration, which would already have
1355 -- been diagnosed at declaration time. Set Label_Construct of the
1356 -- implicit label declaration, which is not created by the parser
1357 -- for generic units.
1359 if Ekind (Ent) = E_Label then
1360 Set_Ekind (Ent, E_Loop);
1362 if Nkind (Parent (Ent)) = N_Implicit_Label_Declaration then
1363 Set_Label_Construct (Parent (Ent), N);
1367 -- Case of no identifier present
1370 Ent := New_Internal_Entity (E_Loop, Current_Scope, Sloc (N), 'L');
1371 Set_Etype (Ent, Standard_Void_Type);
1372 Set_Parent (Ent, N);
1375 -- Kill current values on entry to loop, since statements in body
1376 -- of loop may have been executed before the loop is entered.
1377 -- Similarly we kill values after the loop, since we do not know
1378 -- that the body of the loop was executed.
1380 Kill_Current_Values;
1382 Analyze_Iteration_Scheme (Iteration_Scheme (N));
1383 Analyze_Statements (Statements (N));
1384 Process_End_Label (N, 'e', Ent);
1386 Kill_Current_Values;
1387 end Analyze_Loop_Statement;
1389 ----------------------------
1390 -- Analyze_Null_Statement --
1391 ----------------------------
1393 -- Note: the semantics of the null statement is implemented by a single
1394 -- null statement, too bad everything isn't as simple as this!
1396 procedure Analyze_Null_Statement (N : Node_Id) is
1397 pragma Warnings (Off, N);
1400 end Analyze_Null_Statement;
1402 ------------------------
1403 -- Analyze_Statements --
1404 ------------------------
1406 procedure Analyze_Statements (L : List_Id) is
1411 -- The labels declared in the statement list are reachable from
1412 -- statements in the list. We do this as a prepass so that any
1413 -- goto statement will be properly flagged if its target is not
1414 -- reachable. This is not required, but is nice behavior!
1417 while Present (S) loop
1418 if Nkind (S) = N_Label then
1419 Analyze (Identifier (S));
1420 Lab := Entity (Identifier (S));
1422 -- If we found a label mark it as reachable.
1424 if Ekind (Lab) = E_Label then
1425 Generate_Definition (Lab);
1426 Set_Reachable (Lab);
1428 if Nkind (Parent (Lab)) = N_Implicit_Label_Declaration then
1429 Set_Label_Construct (Parent (Lab), S);
1432 -- If we failed to find a label, it means the implicit declaration
1433 -- of the label was hidden. A for-loop parameter can do this to
1434 -- a label with the same name inside the loop, since the implicit
1435 -- label declaration is in the innermost enclosing body or block
1439 Error_Msg_Sloc := Sloc (Lab);
1441 ("implicit label declaration for & is hidden#",
1449 -- Perform semantic analysis on all statements
1451 Conditional_Statements_Begin;
1454 while Present (S) loop
1459 Conditional_Statements_End;
1461 -- Make labels unreachable. Visibility is not sufficient, because
1462 -- labels in one if-branch for example are not reachable from the
1463 -- other branch, even though their declarations are in the enclosing
1464 -- declarative part.
1467 while Present (S) loop
1468 if Nkind (S) = N_Label then
1469 Set_Reachable (Entity (Identifier (S)), False);
1474 end Analyze_Statements;
1476 --------------------------------------------
1477 -- Check_Possible_Current_Value_Condition --
1478 --------------------------------------------
1480 procedure Check_Possible_Current_Value_Condition (Cnode : Node_Id) is
1484 -- Loop to deal with (ignore for now) any NOT operators present
1486 Cond := Condition (Cnode);
1487 while Nkind (Cond) = N_Op_Not loop
1488 Cond := Right_Opnd (Cond);
1491 -- Check possible relational operator
1493 if Nkind (Cond) = N_Op_Eq
1495 Nkind (Cond) = N_Op_Ne
1497 Nkind (Cond) = N_Op_Ge
1499 Nkind (Cond) = N_Op_Le
1501 Nkind (Cond) = N_Op_Gt
1503 Nkind (Cond) = N_Op_Lt
1505 if Compile_Time_Known_Value (Right_Opnd (Cond))
1506 and then Nkind (Left_Opnd (Cond)) = N_Identifier
1509 Ent : constant Entity_Id := Entity (Left_Opnd (Cond));
1512 if Ekind (Ent) = E_Variable
1514 Ekind (Ent) = E_Constant
1518 Ekind (Ent) = E_Loop_Parameter
1520 -- Here we have a case where the Current_Value field
1521 -- may need to be set. We set it if it is not already
1522 -- set to a compile time expression value.
1524 -- Note that this represents a decision that one
1525 -- condition blots out another previous one. That's
1526 -- certainly right if they occur at the same level.
1527 -- If the second one is nested, then the decision is
1528 -- neither right nor wrong (it would be equally OK
1529 -- to leave the outer one in place, or take the new
1530 -- inner one. Really we should record both, but our
1531 -- data structures are not that elaborate.
1533 if Nkind (Current_Value (Ent)) not in N_Subexpr then
1534 Set_Current_Value (Ent, Cnode);
1540 end Check_Possible_Current_Value_Condition;
1542 ----------------------------
1543 -- Check_Unreachable_Code --
1544 ----------------------------
1546 procedure Check_Unreachable_Code (N : Node_Id) is
1547 Error_Loc : Source_Ptr;
1551 if Is_List_Member (N)
1552 and then Comes_From_Source (N)
1558 Nxt := Original_Node (Next (N));
1561 and then Comes_From_Source (Nxt)
1562 and then Is_Statement (Nxt)
1564 -- Special very annoying exception. If we have a return that
1565 -- follows a raise, then we allow it without a warning, since
1566 -- the Ada RM annoyingly requires a useless return here!
1568 if Nkind (Original_Node (N)) /= N_Raise_Statement
1569 or else Nkind (Nxt) /= N_Return_Statement
1571 -- The rather strange shenanigans with the warning message
1572 -- here reflects the fact that Kill_Dead_Code is very good
1573 -- at removing warnings in deleted code, and this is one
1574 -- warning we would prefer NOT to have removed :-)
1576 Error_Loc := Sloc (Nxt);
1578 -- If we have unreachable code, analyze and remove the
1579 -- unreachable code, since it is useless and we don't
1580 -- want to generate junk warnings.
1582 -- We skip this step if we are not in code generation mode.
1583 -- This is the one case where we remove dead code in the
1584 -- semantics as opposed to the expander, and we do not want
1585 -- to remove code if we are not in code generation mode,
1586 -- since this messes up the ASIS trees.
1588 -- Note that one might react by moving the whole circuit to
1589 -- exp_ch5, but then we lose the warning in -gnatc mode.
1591 if Operating_Mode = Generate_Code then
1595 -- Quit deleting when we have nothing more to delete
1596 -- or if we hit a label (since someone could transfer
1597 -- control to a label, so we should not delete it).
1599 exit when No (Nxt) or else Nkind (Nxt) = N_Label;
1601 -- Statement/declaration is to be deleted
1605 Kill_Dead_Code (Nxt);
1609 -- Now issue the warning
1611 Error_Msg ("?unreachable code", Error_Loc);
1614 -- If the unconditional transfer of control instruction is
1615 -- the last statement of a sequence, then see if our parent
1616 -- is an IF statement, and if so adjust the unblocked exit
1617 -- count of the if statement to reflect the fact that this
1618 -- branch of the if is indeed blocked by a transfer of control.
1623 if Nkind (P) = N_If_Statement then
1626 elsif Nkind (P) = N_Elsif_Part then
1628 pragma Assert (Nkind (P) = N_If_Statement);
1630 elsif Nkind (P) = N_Case_Statement_Alternative then
1632 pragma Assert (Nkind (P) = N_Case_Statement);
1638 Unblocked_Exit_Count := Unblocked_Exit_Count - 1;
1642 end Check_Unreachable_Code;