gcc/domwalk.h

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