gcc/ada/exp_alfa.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                             E X P _ A L F A                              --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 2011-2012, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT; see file COPYING3.  If not, go to --
  19 -- http://www.gnu.org/licenses for a complete copy of the license.          --
  20 --                                                                          --
  21 -- GNAT was originally developed  by the GNAT team at  New York University. --
  22 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  23 --                                                                          --
  24 ------------------------------------------------------------------------------
  25
  26 --  This package implements a light expansion which is used in formal
  27 --  verification mode (Alfa_Mode = True). Instead of a complete expansion
  28 --  of nodes for code generation, this Alfa expansion targets generation
  29 --  of intermediate code for formal verification.
  30
  31 --  Expand_Alfa is called directly by Expander.Expand.
  32
  33 --  Alfa expansion has three main objectives:
  34
  35 --    1. Perform limited expansion to explicit some Ada rules and constructs
  36 --       (translate 'Old and 'Result, replace renamings by renamed, insert
  37 --        conversions, expand actuals in calls to introduce temporaries, expand
  38 --        generics instantiations)
  39
  40 --    2. Facilitate treatment for the formal verification back-end (fully
  41 --       qualify names, expand set membership, compute data dependences)
  42
  43 --    3. Avoid the introduction of low-level code that is difficult to analyze
  44 --       formally, as typically done in the full expansion for high-level
  45 --       constructs (tasking, dispatching)
  46
  47 --  To fulfill objective 1, Expand_Alfa selectively expands some constructs.
  48
  49 --  To fulfill objective 2, the tree after Alfa expansion should be fully
  50 --  analyzed semantically. In particular, all expression must have their proper
  51 --  type, and semantic links should be set between tree nodes (partial to full
  52 --  view, etc.) Some kinds of nodes should be either absent, or can be ignored
  53 --  by the formal verification backend:
  54
  55 --      N_Object_Renaming_Declaration: can be ignored safely
  56 --      N_Expression_Function:         absent (rewitten)
  57 --      N_Expression_With_Actions:     absent (not generated)
  58
  59 --  Alfa cross-references are generated from the regular cross-references (used
  60 --  for browsing and code understanding) and additional references collected
  61 --  during semantic analysis, in particular on all dereferences. These Alfa
  62 --  cross-references are output in a separate section of ALI files, as
  63 --  described in alfa.adb. They are the basis for the computation of data
  64 --  dependences in the formal verification backend. This implies that all
  65 --  cross-references should be generated in this mode, even those that would
  66 --  not make sense from a user point-of-view, and that cross-references that do
  67 --  not lead to data dependences for subprograms can be safely ignored.
  68
  69 --  To support the formal verification of units parameterized by data, the
  70 --  value of deferred constants should not be considered as a compile-time
  71 --  constant at program locations where the full view is not visible.
  72
  73 --  To fulfill objective 3, Expand_Alfa does not expand features that are not
  74 --  formally analyzed (tasking), or for which formal analysis relies on the
  75 --  source level representation (dispatching, aspects, pragmas). However, these
  76 --  should be semantically analyzed, which sometimes requires the insertion of
  77 --  semantic pre-analysis, for example for subprogram contracts and pragma
  78 --  check/assert.
  79
  80 with Types; use Types;
  81
  82 package Exp_Alfa is
  83
  84    procedure Expand_Alfa (N : Node_Id);
  85
  86 end Exp_Alfa;