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1 /* Generic dominator tree walker
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2 Copyright (C) 2003-2018 Free Software Foundation, Inc.
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3 Contributed by Diego Novillo <dnovillo@redhat.com>
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4
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5 This file is part of GCC.
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6
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7 GCC is free software; you can redistribute it and/or modify
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8 it under the terms of the GNU General Public License as published by
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9 the Free Software Foundation; either version 3, or (at your option)
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10 any later version.
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11
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12 GCC is distributed in the hope that it will be useful,
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13 but WITHOUT ANY WARRANTY; without even the implied warranty of
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14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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15 GNU General Public License for more details.
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16
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17 You should have received a copy of the GNU General Public License
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18 along with GCC; see the file COPYING3. If not see
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19 <http://www.gnu.org/licenses/>. */
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20
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111
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21 #ifndef GCC_DOM_WALK_H
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22 #define GCC_DOM_WALK_H
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23
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24 /**
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25 * This is the main class for the dominator walker. It is expected that
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26 * consumers will have a custom class inheriting from it, which will over ride
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27 * at least one of before_dom_children and after_dom_children to implement the
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28 * custom behavior.
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29 */
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30 class dom_walker
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31 {
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32 public:
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33 static const edge STOP;
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34
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35 /* An enum for determining whether the dom walk should be constrained to
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36 blocks reachable by executable edges. */
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37
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38 enum reachability
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39 {
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40 /* Walk all blocks within the CFG. */
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41 ALL_BLOCKS,
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42
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43 /* Use REACHABLE_BLOCKS when your subclass can discover that some edges
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44 are not executable.
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45
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46 If a subclass can discover that a COND, SWITCH or GOTO has a static
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47 target in the before_dom_children callback, the taken edge should
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48 be returned. The generic walker will clear EDGE_EXECUTABLE on all
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49 edges it can determine are not executable.
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50
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51 With REACHABLE_BLOCKS, EDGE_EXECUTABLE will be set on every edge in
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52 the dom_walker ctor; the flag will then be cleared on edges that are
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53 determined to be not executable. */
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54 REACHABLE_BLOCKS,
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55
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56 /* Identical to REACHABLE_BLOCKS, but the initial state of EDGE_EXECUTABLE
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57 will instead be preserved in the ctor, allowing for information about
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58 non-executable edges to be merged in from an earlier analysis (and
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59 potentially for additional edges to be marked as non-executable). */
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60 REACHABLE_BLOCKS_PRESERVING_FLAGS
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61 };
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62
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63 dom_walker (cdi_direction direction, enum reachability = ALL_BLOCKS);
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64
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65 /* You can provide a mapping of basic-block index to RPO if you
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66 have that readily available or you do multiple walks. If you
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67 specify NULL as BB_INDEX_TO_RPO dominator children will not be
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68 walked in RPO order. */
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69 dom_walker (cdi_direction direction, enum reachability, int *bb_index_to_rpo);
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70
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71 ~dom_walker ();
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72
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73 /* Walk the dominator tree. */
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74 void walk (basic_block);
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75
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76 /* Function to call before the recursive walk of the dominator children.
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77
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78 Return value is the always taken edge if the block has multiple outgoing
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79 edges, NULL otherwise. When skipping unreachable blocks, the walker
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80 uses the taken edge information to clear EDGE_EXECUTABLE on the other
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81 edges, exposing unreachable blocks. A NULL return value means all
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82 outgoing edges should still be considered executable. A return value
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83 of STOP means to stop the domwalk from processing dominated blocks from
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84 here. This can be used to process a SEME region only (note domwalk
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85 will still do work linear in function size). */
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86 virtual edge before_dom_children (basic_block) { return NULL; }
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87
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88 /* Function to call after the recursive walk of the dominator children. */
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89 virtual void after_dom_children (basic_block) {}
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90
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91 private:
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92 /* This is the direction of the dominator tree we want to walk. i.e.,
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93 if it is set to CDI_DOMINATORS, then we walk the dominator tree,
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94 if it is set to CDI_POST_DOMINATORS, then we walk the post
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95 dominator tree. */
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96 const ENUM_BITFIELD (cdi_direction) m_dom_direction : 2;
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97 bool m_skip_unreachable_blocks;
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98 bool m_user_bb_to_rpo;
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99 basic_block m_unreachable_dom;
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100 int *m_bb_to_rpo;
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101
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102 /* Query whether or not the given block is reachable or not. */
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103 bool bb_reachable (struct function *, basic_block);
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104
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105 /* Given an unreachable block, propagate that property to outgoing
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106 and possibly incoming edges for the block. Typically called after
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107 determining a block is unreachable in the before_dom_children
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108 callback. */
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109 void propagate_unreachable_to_edges (basic_block, FILE *, dump_flags_t);
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110
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111 };
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112
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113 extern void set_all_edges_as_executable (function *fn);
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114
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115 #endif
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