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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;
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