--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/ada/expander.ads	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,169 @@
+------------------------------------------------------------------------------
+--                                                                          --
+--                         GNAT COMPILER COMPONENTS                         --
+--                                                                          --
+--                             E X P A N D E R                              --
+--                                                                          --
+--                                 S p e c                                  --
+--                                                                          --
+--          Copyright (C) 1992-2016, Free Software Foundation, Inc.         --
+--                                                                          --
+-- GNAT is free software;  you can  redistribute it  and/or modify it under --
+-- terms of the  GNU General Public License as published  by the Free Soft- --
+-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
+-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
+-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
+-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
+-- for  more details.  You should have  received  a copy of the GNU General --
+-- Public License  distributed with GNAT; see file COPYING3.  If not, go to --
+-- http://www.gnu.org/licenses for a complete copy of the license.          --
+--                                                                          --
+-- GNAT was originally developed  by the GNAT team at  New York University. --
+-- Extensive contributions were provided by Ada Core Technologies Inc.      --
+--                                                                          --
+------------------------------------------------------------------------------
+
+--  This procedure performs any required expansion for the specified node.
+--  The argument is the node that is a candidate for possible expansion.
+--  If no expansion is required, then Expand returns without doing anything.
+
+--  If the node does need expansion, then the subtree is replaced by the
+--  tree corresponding to the required rewriting. This tree is a syntactic
+--  tree, except that all Entity fields must be correctly set on all
+--  direct names, since the expander presumably knows what it wants, and in
+--  any case it doesn't work to have the semantic analyzer perform visibility
+--  analysis on these trees (they may have references to non-visible runtime
+--  routines etc.) There are a few exceptions to this rule in special cases,
+--  but they must be documented clearly.
+
+--  Expand is called in two different situations:
+
+--    Nodes that are not subexpressions (Nkind not in N_Subexpr)
+
+--      In this case, Expand is called from the body of Sem, immediately
+--      after completing semantic analysis by calling the corresponding
+--      Analyze_N_xxx procedure. If expansion occurs, the given node must
+--      be replaced with another node that is also not a subexpression.
+--      This seems naturally to be the case, since it is hard to imagine any
+--      situation in which it would make sense to replace a non-expression
+--      subtree with an expression. Once the substitution is completed, the
+--      Expand routine must call Analyze on the resulting node to do any
+--      required semantic analysis. Note that references to children copied
+--      from the old tree won't be reanalyzed, since their Analyzed flag
+--      is set.
+
+--    Nodes that are subexpressions (Nkind in N_Subexpr)
+
+--      In this case, Expand is called from Sem_Res.Resolve after completing
+--      the resolution of the subexpression (this means that the expander sees
+--      the fully typed subtree). If expansion occurs, the given node must be
+--      replaced by a node that is also a subexpression. Again it is hard
+--      to see how this restriction could possibly be violated. Once the
+--      substitution is completed, the Expand routine must first call Analyze
+--      on the resulting node to do any required semantic analysis, and then
+--      call Resolve on the node to set the type (typically the type will be
+--      the same as the original type of the input node, but this is not
+--      always the case).
+
+--  In both these cases, Replace or Rewrite must be used to achieve the
+--  expansion of the node, since the Expander routine is only passed the
+--  Node_Id of the node to be expanded, and the resulting expanded Node_Id
+--  must be the same (the parameter to Expand is mode in, not mode in-out).
+
+--  For nodes other than subexpressions, it is not necessary to preserve the
+--  original tree in the Expand routines, unlike the case for modifications
+--  to the tree made in the semantic analyzer. This is because anyone who is
+--  interested in working with the original tree (like ASIS) is required to
+--  compile in semantics checks only mode. Thus Replace may be freely used
+--  in such instances.
+
+--  For subexpressions, preservation of the original tree is required because
+--  of the need for conformance checking of default expressions, which occurs
+--  on expanded trees. This means that Replace should not ever be used on
+--  on subexpression nodes. Instead use Rewrite.
+
+--  Note: the front end avoids calls to any of the expand routines if code
+--  is not being generated. This is done for three reasons:
+
+--    1.  Make sure tree does not get mucked up by the expander if no
+--        code is being generated, and is thus usable by ASIS etc.
+
+--    2.  Save time, since expansion is not needed if a compilation is
+--        being done only to check the semantics, or if code generation
+--        has been canceled due to previously detected errors.
+
+--    3.  Allow the expand routines to assume that the tree is error free.
+--        This results from the fact that code generation mode is always
+--        cancelled when any error occurs.
+
+--  If we ever decide to implement a feature allowing object modules to be
+--  generated even if errors have been detected, then point 3 will no longer
+--  hold, and the expand routines will have to be modified to operate properly
+--  in the presence of errors (for many reasons this is not currently true).
+
+--  Note: a consequence of this approach is that error messages must never
+--  be generated in the expander, since this would mean that such error
+--  messages are not generated when the expander is not being called.
+
+--  Expansion is the last stage of analyzing a node, so Expand sets the
+--  Analyzed flag of the node being analyzed as its last action. This is
+--  done even if expansion is off (in this case, the only effect of the
+--  call to Expand is to set the Analyzed flag to True).
+
+with Types; use Types;
+
+package Expander is
+
+   --  The flag Opt.Expander_Active controls whether expansion is active
+   --  (True) or deactivated (False). When expansion is deactivated all
+   --  calls to expander routines have no effect. To temporarily disable
+   --  expansion, always call the routines defined below, do NOT change
+   --  Expander_Active directly.
+   --
+   --  You should not use this flag to test if you are currently processing
+   --  a generic spec or body. Use the flag Inside_A_Generic instead (see
+   --  the spec of package Sem).
+   --
+   --  There is no good reason for permanently changing the value of this flag
+   --  except after detecting a syntactic or semantic error. In this event
+   --  this flag is set to False to disable all subsequent expansion activity.
+   --
+   --  In general this flag should be used as a read only value. The only
+   --  exceptions where it makes sense to temporarily change its value are:
+   --
+   --    (a) when starting/completing the processing of a generic definition
+   --        or declaration (see routines Start_Generic_Processing and
+   --        End_Generic_Processing in Sem_Ch12)
+   --
+   --    (b) when starting/completing the pre-analysis of an expression
+   --        (see the spec of package Sem for more info on pre-analysis.)
+   --
+   --  Note that when processing a spec expression (In_Spec_Expression
+   --  is True) or performing semantic analysis of a generic spec or body
+   --  (Inside_A_Generic) or when performing pre-analysis (Full_Analysis is
+   --  False) the Expander_Active flag is False.
+
+   procedure Expand (N : Node_Id);
+   --  Expand node N, as described above
+
+   procedure Expander_Mode_Save_And_Set (Status : Boolean);
+   --  Saves the current setting of the Expander_Active flag on an internal
+   --  stack and then sets the flag to the given value.
+   --
+   --  Note: this routine has no effect in ASIS and GNATprove modes. In ASIS
+   --  mode, all expansion activity is always off, since we want the original
+   --  semantic tree for ASIS purposes without any expansion. In GNATprove
+   --  mode, a very light expansion is performed on specific nodes. Both are
+   --  achieved by setting Expander_Active False in ASIS and GNATprove modes.
+   --  In situations such as the call to Instantiate_Bodies in Frontend,
+   --  Expander_Mode_Save_And_Set may be called to temporarily turn the
+   --  expander on, but this will have no effect in ASIS and GNATprove modes.
+
+   procedure Expander_Mode_Restore;
+   --  Restores the setting of the Expander_Active flag using the top entry
+   --  pushed onto the stack by Expander_Mode_Save_And_Reset, popping the
+   --  stack, except that if any errors have been detected, then the state of
+   --  the flag is left set to False. Disabled for ASIS and GNATprove modes
+   --  (see above).
+
+end Expander;