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------------------------------------------------------------------------------ -- -- -- 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;
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