dominators_example.cc

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
 
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
 
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
*/
 
 
#include <iostream>
#include <string>
#include <Dominators.H>
#include <tpl_graph.H>
 
using namespace std;
using namespace Aleph;
 
namespace
{
  using CFG = List_Digraph<Graph_Node<string>, Graph_Arc<int>>;
 
  template <typename Container>
  void print_frontier(CFG::Node * node, const Container & frontier)
  {
    (void) node;
    cout << "{";
    bool first = true;
    for (auto fi = frontier.get_it(); fi.has_curr(); fi.next_ne())
      {
        if (not first)
          cout << ", ";
        cout << fi.get_curr()->get_info();
        first = false;
      }
    cout << "}";
  }
} // namespace
 
 
int main()
{
  // ========================================================================
  // 1. Build a control-flow graph
  // ========================================================================
  //
  //  entry
  //    |
  //  cond
  //  |- then
  //  `- else
  //  join
  //    |
  //  loop_header <----+
  //    |      |       |
  //  loop_body |      |
  //    |      |       |
  //    +------+-------+
  //    |
  //   exit
 
  CFG cfg;
 
  auto entry       = cfg.insert_node("entry");
  auto cond        = cfg.insert_node("cond");
  auto then_block  = cfg.insert_node("then");
  auto else_block  = cfg.insert_node("else");
  auto join        = cfg.insert_node("join");
  auto loop_header = cfg.insert_node("loop_hdr");
  auto loop_body   = cfg.insert_node("loop_body");
  auto exit_block  = cfg.insert_node("exit");
 
  cfg.insert_arc(entry, cond);
  cfg.insert_arc(cond, then_block);
  cfg.insert_arc(cond, else_block);
  cfg.insert_arc(then_block, join);
  cfg.insert_arc(else_block, join);
  cfg.insert_arc(join, loop_header);
  cfg.insert_arc(loop_header, loop_body);
  cfg.insert_arc(loop_header, exit_block);
  cfg.insert_arc(loop_body, loop_header);  // back-edge
 
  cout << "=== Control-Flow Graph ===" << endl;
  cout << "Nodes: " << cfg.get_num_nodes() << endl;
  cout << "Arcs:  " << cfg.get_num_arcs() << endl;
  cout << endl;
  cout << "Edges:" << endl;
  for (auto it = cfg.get_arc_it(); it.has_curr(); it.next_ne())
    {
      auto arc = it.get_curr();
      cout << "  " << cfg.get_src_node(arc)->get_info()
           << " -> " << cfg.get_tgt_node(arc)->get_info() << endl;
    }
  cout << endl;
 
  // ========================================================================
  // 2. Compute immediate dominators
  // ========================================================================
 
  Lengauer_Tarjan_Dominators<CFG> dom;
  auto idoms = dom.compute_idom(cfg, entry);
 
  cout << "=== Immediate Dominators ===" << endl;
  for (auto it = idoms.get_it(); it.has_curr(); it.next_ne())
    {
      auto [node, idom] = it.get_curr();
      cout << "  idom(" << node->get_info() << ") = "
           << (idom ? idom->get_info() : "(root)") << endl;
    }
  cout << endl;
 
  // ========================================================================
  // 3. Build and display dominator tree
  // ========================================================================
 
  CFG dom_tree;
  dom.build_tree(cfg, entry, dom_tree);
 
  cout << "=== Dominator Tree ===" << endl;
  cout << "Nodes: " << dom_tree.get_num_nodes() << endl;
  cout << "Arcs:  " << dom_tree.get_num_arcs() << endl;
  cout << endl;
  cout << "Tree edges (parent -> child):" << endl;
  for (auto it = dom_tree.get_arc_it(); it.has_curr(); it.next_ne())
    {
      auto arc = it.get_curr();
      cout << "  " << dom_tree.get_src_node(arc)->get_info()
           << " -> " << dom_tree.get_tgt_node(arc)->get_info() << endl;
    }
  cout << endl;
 
  // ========================================================================
  // 4. Compute dominance frontiers (for SSA phi-function placement)
  // ========================================================================
 
  auto df = dom.dominance_frontiers(cfg, entry);
 
  cout << "=== Dominance Frontiers ===" << endl;
  for (auto it = df.get_it(); it.has_curr(); it.next_ne())
    {
      auto & [node, frontier] = it.get_curr();
      cout << "  DF(" << node->get_info() << ") = ";
      print_frontier(node, frontier);
      cout << endl;
    }
  cout << endl;
 
  // ========================================================================
  // 5. Identify phi-function placement
  // ========================================================================
 
  cout << "=== SSA Phi-Function Placement ===" << endl;
  cout << "Blocks where phi-functions would be needed:" << endl;
 
  // In SSA, phi-functions are placed at dominance frontier nodes.
  // A variable defined in block B needs a phi at each node in DF(B).
  for (auto it = df.get_it(); it.has_curr(); it.next_ne())
    {
      auto & [node, frontier] = it.get_curr();
      if (not frontier.is_empty())
        {
          cout << "  Definitions in '" << node->get_info()
               << "' need phi at: ";
          print_frontier(node, frontier);
          cout << endl;
        }
    }
  cout << endl;
 
  // ========================================================================
  // 6. Dominance queries
  // ========================================================================
 
  cout << "=== Dominance Queries ===" << endl;
  cout << "  entry dominates exit?  "
       << (dom.dominates(cfg, entry, entry, exit_block) ? "yes" : "no") << endl;
  cout << "  cond dominates join?   "
       << (dom.dominates(cfg, entry, cond, join) ? "yes" : "no") << endl;
  cout << "  then dominates join?   "
       << (dom.dominates(cfg, entry, then_block, join) ? "yes" : "no") << endl;
  cout << "  loop_hdr dominates loop_body? "
       << (dom.dominates(cfg, entry, loop_header, loop_body) ? "yes" : "no") << endl;
  cout << endl;
 
  // ========================================================================
  // 7. Compute post-dominators (from exit node)
  // ========================================================================
 
  Lengauer_Tarjan_Post_Dominators<CFG> pdom;
  auto ipdoms = pdom.compute_ipdom(cfg, exit_block);
 
  cout << "=== Immediate Post-Dominators (exit = " << exit_block->get_info()
       << ") ===" << endl;
  for (auto pit = ipdoms.get_it(); pit.has_curr(); pit.next_ne())
    {
      auto [node, ipdom] = pit.get_curr();
      cout << "  ipdom(" << node->get_info() << ") = "
           << (ipdom ? ipdom->get_info() : "(exit)") << endl;
    }
  cout << endl;
 
  // ========================================================================
  // 8. Build and display post-dominator tree
  // ========================================================================
 
  CFG pdom_tree;
  pdom.build_tree(cfg, exit_block, pdom_tree);
 
  cout << "=== Post-Dominator Tree ===" << endl;
  cout << "Nodes: " << pdom_tree.get_num_nodes() << endl;
  cout << "Arcs:  " << pdom_tree.get_num_arcs() << endl;
  cout << endl;
  cout << "Tree edges (parent -> child):" << endl;
  for (auto pit = pdom_tree.get_arc_it(); pit.has_curr(); pit.next_ne())
    {
      auto arc = pit.get_curr();
      cout << "  " << pdom_tree.get_src_node(arc)->get_info()
           << " -> " << pdom_tree.get_tgt_node(arc)->get_info() << endl;
    }
  cout << endl;
 
  // ========================================================================
  // 9. Compute post-dominance frontiers (for CDG construction)
  // ========================================================================
 
  auto pdf = pdom.post_dominance_frontiers(cfg, exit_block);
 
  cout << "=== Post-Dominance Frontiers ===" << endl;
  for (auto pit = pdf.get_it(); pit.has_curr(); pit.next_ne())
    {
      auto & [node, frontier] = pit.get_curr();
      cout << "  PDF(" << node->get_info() << ") = ";
      print_frontier(node, frontier);
      cout << endl;
    }
  cout << endl;
 
  // ========================================================================
  // 10. Post-dominance queries
  // ========================================================================
 
  cout << "=== Post-Dominance Queries ===" << endl;
  cout << "  exit post-dominates entry?    "
       << (pdom.post_dominates(cfg, exit_block, exit_block, entry) ? "yes" : "no")
       << endl;
  cout << "  loop_hdr post-dominates cond? "
       << (pdom.post_dominates(cfg, exit_block, loop_header, cond) ? "yes" : "no")
       << endl;
  cout << "  then post-dominates entry?    "
       << (pdom.post_dominates(cfg, exit_block, then_block, entry) ? "yes" : "no")
       << endl;
 
  return 0;
}