1  /* Generic dominator tree walker
       2     Copyright (C) 2003-2023 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    /* You can provide a mapping of basic-block index to RPO if you
      64       have that readily available or you do multiple walks.  If you
      65       specify NULL as BB_INDEX_TO_RPO this mapping will be computed
      66       lazily at walk time.  If you specify -1 dominator children will
      67       not be walked in RPO order.  */
      68    dom_walker (cdi_direction direction, enum reachability = ALL_BLOCKS,
      69  	      int *bb_index_to_rpo = NULL);
      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    const ENUM_BITFIELD (reachability) m_reachability : 2;
      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