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+------------------------------------------------------------------------------
+-- --
+-- GNAT COMPILER COMPONENTS --
+-- --
+-- E X P _ A L F A --
+-- --
+-- S p e c --
+-- --
+-- Copyright (C) 2011-2012, 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 package implements a light expansion which is used in formal
+-- verification mode (Alfa_Mode = True). Instead of a complete expansion
+-- of nodes for code generation, this Alfa expansion targets generation
+-- of intermediate code for formal verification.
+
+-- Expand_Alfa is called directly by Expander.Expand.
+
+-- Alfa expansion has three main objectives:
+
+-- 1. Perform limited expansion to explicit some Ada rules and constructs
+-- (translate 'Old and 'Result, replace renamings by renamed, insert
+-- conversions, expand actuals in calls to introduce temporaries, expand
+-- generics instantiations)
+
+-- 2. Facilitate treatment for the formal verification back-end (fully
+-- qualify names, expand set membership, compute data dependences)
+
+-- 3. Avoid the introduction of low-level code that is difficult to analyze
+-- formally, as typically done in the full expansion for high-level
+-- constructs (tasking, dispatching)
+
+-- To fulfill objective 1, Expand_Alfa selectively expands some constructs.
+
+-- To fulfill objective 2, the tree after Alfa expansion should be fully
+-- analyzed semantically. In particular, all expression must have their proper
+-- type, and semantic links should be set between tree nodes (partial to full
+-- view, etc.) Some kinds of nodes should be either absent, or can be ignored
+-- by the formal verification backend:
+
+-- N_Object_Renaming_Declaration: can be ignored safely
+-- N_Expression_Function: absent (rewitten)
+-- N_Expression_With_Actions: absent (not generated)
+
+-- Alfa cross-references are generated from the regular cross-references (used
+-- for browsing and code understanding) and additional references collected
+-- during semantic analysis, in particular on all dereferences. These Alfa
+-- cross-references are output in a separate section of ALI files, as
+-- described in alfa.adb. They are the basis for the computation of data
+-- dependences in the formal verification backend. This implies that all
+-- cross-references should be generated in this mode, even those that would
+-- not make sense from a user point-of-view, and that cross-references that do
+-- not lead to data dependences for subprograms can be safely ignored.
+
+-- To support the formal verification of units parameterized by data, the
+-- value of deferred constants should not be considered as a compile-time
+-- constant at program locations where the full view is not visible.
+
+-- To fulfill objective 3, Expand_Alfa does not expand features that are not
+-- formally analyzed (tasking), or for which formal analysis relies on the
+-- source level representation (dispatching, aspects, pragmas). However, these
+-- should be semantically analyzed, which sometimes requires the insertion of
+-- semantic pre-analysis, for example for subprogram contracts and pragma
+-- check/assert.
+
+with Types; use Types;
+
+package Exp_Alfa is
+
+ procedure Expand_Alfa (N : Node_Id);
+
+end Exp_Alfa;