aboutsummaryrefslogtreecommitdiffstats
path: root/gcc-4.8.3/gcc/ada/expander.ads
diff options
context:
space:
mode:
Diffstat (limited to 'gcc-4.8.3/gcc/ada/expander.ads')
-rw-r--r--gcc-4.8.3/gcc/ada/expander.ads167
1 files changed, 167 insertions, 0 deletions
diff --git a/gcc-4.8.3/gcc/ada/expander.ads b/gcc-4.8.3/gcc/ada/expander.ads
new file mode 100644
index 000000000..df5944218
--- /dev/null
+++ b/gcc-4.8.3/gcc/ada/expander.ads
@@ -0,0 +1,167 @@
+------------------------------------------------------------------------------
+-- --
+-- GNAT COMPILER COMPONENTS --
+-- --
+-- E X P A N D E R --
+-- --
+-- S p e c --
+-- --
+-- Copyright (C) 1992-2008, 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
+-- 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_Mode. In ASIS_Mode, all
+ -- expansion activity is always off, since we want the original semantic
+ -- tree for ASIS purposes without any expansion. This is achieved by
+ -- setting Expander_Active False in ASIS_Mode. 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 mode.
+
+ 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_Mode (see above).
+
+end Expander;