New Language: Ada

From-SVN: r45959

1 files changed, 1256 insertions, 0 deletions

diff --git a/gcc/ada/sem_ch5.adb b/gcc/ada/sem_ch5.adb
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@@ -0,0 +1,1256 @@
+------------------------------------------------------------------------------
+--                                                                          --
+--                         GNAT COMPILER COMPONENTS                         --
+--                                                                          --
+--                              S E M _ C H 5                               --
+--                                                                          --
+--                                 B o d y                                  --
+--                                                                          --
+--                            $Revision: 1.262 $
+--                                                                          --
+--          Copyright (C) 1992-2001 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. --
+-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
+--                                                                          --
+------------------------------------------------------------------------------
+
+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, 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');
+
+      --  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 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
+         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
+
+                  if Nkind (DS) = N_Range
+                    and then Comes_From_Source (N)
+                    and then not Inside_A_Generic
+                  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
+                           Warn_On_Instance := True;
+                           Error_Msg_N
+                             ("?loop range is null, loop will not execute",
+                              DS);
+                           Warn_On_Instance := False;
+
+                        --  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');
+      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
+   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;