[DRAFT][compiler] Introduce EliminateDeadSubgraphPass

This pr introduces EliminateDeadSubgraphPass for removing dead subgraph.

ONE-DCO-1.0-Signed-off-by: Artem Balyshev <[email protected]>

compiler/circle2circle/src/Circle2Circle.cpp

@@ -518,7 +518,7 @@ int entry(int argc, char **argv)
     luci::change_outputs(graph, new_outputs);
   }
 
-  // call luci optimizations for module
+  // call luci optimizations for module before optimizations for graph
   optimizer.optimize(module.get());
 
   for (size_t idx = 0; idx < module->size(); ++idx)
@@ -541,6 +541,9 @@ int entry(int argc, char **argv)
     }
   }
 
+  // call luci optimizations for module after optimizations for graph
+  optimizer.optimize(module.get());
+
   // Export to output Circle file
   luci::CircleExporter exporter;
 

compiler/luci/lang/include/luci/IR/Module.h

@@ -51,6 +51,13 @@ class Module final
    */
   loco::Graph *graph(void) const;
 
+  /**
+   * @brief remove graph at index
+   *
+   * @note  graph(0) is interpreted as a main graph and cannot be deleted
+   */
+  void removeGraphByIndex(size_t idx);
+
   /**
    * @brief provide graph with an index
    *

compiler/luci/lang/src/Module.cpp

@@ -35,6 +35,14 @@ loco::Graph *Module::graph(void) const
   return graph.get();
 }
 
+void Module::removeGraphByIndex(size_t idx)
+{
+  if (idx >= _graphs.size() or idx == 0)
+    throw std::invalid_argument("Module: Invalid graph index to be deleted");
+
+  _graphs.erase(_graphs.begin() + idx);
+}
+
 loco::Graph *Module::graph(size_t idx) const
 {
   auto &graph = _graphs.at(idx);

compiler/luci/lang/src/Module.test.cpp

@@ -37,6 +37,33 @@ TEST(ModuleTest, add)
   ASSERT_EQ(g_ptr, m->graph(0));
 }
 
+TEST(ModuleTest, remove)
+{
+  auto m = luci::make_module();
+  auto g1 = loco::make_graph();
+  auto g2 = loco::make_graph();
+  auto g3 = loco::make_graph();
+  auto g1_ptr = g1.get();
+  auto g2_ptr = g2.get();
+  auto g3_ptr = g3.get();
+
+  m->add(std::move(g1));
+  m->add(std::move(g2));
+  m->add(std::move(g3));
+
+  ASSERT_EQ(3, m->size());
+  ASSERT_EQ(g1_ptr, m->graph());
+  ASSERT_EQ(g1_ptr, m->graph(0));
+  ASSERT_EQ(g2_ptr, m->graph(1));
+  ASSERT_EQ(g3_ptr, m->graph(2));
+
+  // Let's delete graph at second position
+  m->removeGraphByIndex(1);
+  ASSERT_EQ(2, m->size());
+  ASSERT_EQ(g1_ptr, m->graph(0));
+  ASSERT_EQ(g3_ptr, m->graph(1));
+}
+
 TEST(ModuleTest, add_more)
 {
   auto m = luci::make_module();
@@ -65,6 +92,13 @@ TEST(ModuleTest, add_nullptr_NEG)
   EXPECT_THROW(m->add(nullptr), std::invalid_argument);
 }
 
+TEST(ModuleTest, remove_index_overflow_NEG)
+{
+  auto m = luci::make_module();
+
+  EXPECT_THROW(m->removeGraphByIndex(10), std::invalid_argument);
+}
+
 TEST(ModuleTest, graph_index_overflow_NEG)
 {
   auto m = luci::make_module();

compiler/luci/pass/include/luci/Pass/EliminateDeadSubgraphPass.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2024 Samsung Electronics Co., Ltd. All Rights Reserved
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __LUCI_ELIMINATE_DEAD_SUBGRAPH_PASS_H__
+#define __LUCI_ELIMINATE_DEAD_SUBGRAPH_PASS_H__
+
+#include <logo/Pass.h>
+#include <luci/ModulePass.h>
+#include <luci/IR/Module.h>
+
+namespace luci
+{
+
+/**
+ * @brief  Class to eliminate dead subgraph
+ *
+ */
+struct EliminateDeadSubgraphPass final : public luci::Pass
+{
+  const char *name(void) const final { return "luci::EliminateDeadSubgraphPass"; }
+
+  bool run(luci::Module *m);
+  bool run(loco::Graph *)
+  {
+    // Do nothing
+    return false;
+  }
+};
+
+} // namespace luci
+
+#endif // __LUCI_ELIMINATE_DEAD_SUBGRAPH_PASS_H__

compiler/luci/pass/src/CircleOptimizer.cpp

@@ -101,6 +101,7 @@
 
 #include "luci/Pass/CircleShapeInferencePass.h"
 #include "luci/Pass/CircleTypeInferencePass.h"
+#include "luci/Pass/EliminateDeadSubgraphPass.h"
 
 // logo passes
 #include <logo/RemoveDeadNodeWithQueryPass.h>
@@ -246,6 +247,8 @@ void CircleOptimizer::optimize(luci::Module *m) const
     phase.emplace_back(std::make_unique<FuseBCQPass>());
   }
 
+  phase.emplace_back(std::make_unique<luci::EliminateDeadSubgraphPass>());
+
   ModuleProgressReporter prog(m, logo::PhaseStrategy::Restart);
   PhaseRunner<logo::PhaseStrategy::Restart> phase_runner{m};
   phase_runner.attach(&prog);

compiler/luci/pass/src/EliminateDeadSubgraphPass.cpp

@@ -0,0 +1,148 @@
+/*
+ * Copyright (c) 2024 Samsung Electronics Co., Ltd. All Rights Reserved
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "luci/Pass/EliminateDeadSubgraphPass.h"
+
+#include <luci/IR/CircleNodes.h>
+
+#include <unordered_set>
+#include <deque>
+
+namespace luci
+{
+
+namespace
+{
+
+// Go through the current graph and check all other graphs reachable from it and save it.
+// Note: The main idea for finding achievable graphs is that we can get into other graphs only
+// from some operations (see the list below) and we check the graph numbers from these operations.
+void checkGraph(loco::Graph *current_graph, std::deque<size_t> &reachable_graphs_indexes_q)
+{
+  assert(current_graph != nullptr);
+
+  // 1 - Obtain all active nodes in current graph
+  // 2 - Go through all active nodes and check its types
+  // 3 - If it is possible to get to another graph from the operation (see the list below),
+  //     then add the graph numbers to our queue
+
+  // 1 - Obtain all active nodes in current graph
+  // Let's enumerate nodes required to compute output nodes
+  auto active_nodes = loco::active_nodes(loco::output_nodes(current_graph));
+
+  // 2 - Go through all active nodes and check its types
+  // Nodes from we can obtain different subgraph:
+  // While, If, ...
+  // TODO: check all nodes which can be used to reach different subgraph
+  for (auto &node : active_nodes)
+  {
+    auto *circle_node = dynamic_cast<luci::CircleNode *>(node);
+    assert(circle_node != nullptr);
+
+    switch (circle_node->opcode())
+    {
+      case CircleOpcode::WHILE:
+      {
+        auto *while_node = dynamic_cast<luci::CircleWhile *>(circle_node);
+        assert(while_node != nullptr);
+        // Get body and cond graph indexes
+        int32_t body_graph_index = while_node->body_branch();
+        int32_t cond_graph_index = while_node->cond_branch();
+        assert(body_graph_index >= 0);
+        assert(cond_graph_index >= 0);
+        // Add indexes into queue
+        reachable_graphs_indexes_q.push_back(size_t(body_graph_index));
+        reachable_graphs_indexes_q.push_back(size_t(cond_graph_index));
+      }
+      break;
+      case CircleOpcode::IF:
+      {
+        auto *if_node = dynamic_cast<luci::CircleIf *>(circle_node);
+        assert(if_node != nullptr);
+        // Get then and else graph indexes
+        int32_t else_index = if_node->else_branch();
+        int32_t then_index = if_node->then_branch();
+        assert(else_index >= 0);
+        assert(then_index >= 0);
+        // Add indexes into queue
+        reachable_graphs_indexes_q.push_back(size_t(else_index));
+        reachable_graphs_indexes_q.push_back(size_t(then_index));
+      }
+      break;
+      default:
+        continue;
+    }
+  }
+}
+
+} // namespace
+
+/**
+ * Eliminate dead subgraph.
+ * Note: dead means inaccessible from the main (with index zero) graph
+ **/
+bool EliminateDeadSubgraphPass::run(luci::Module *m)
+{
+  bool changed = false;
+
+  if (m->size() == 0)
+    throw std::invalid_argument("No any graphs");
+
+  // Nothing check
+  if (m->size() == 1)
+    return false;
+
+  std::unordered_set<size_t> reachable_indexes;
+
+  // Queue with reachable graphs indexes
+  std::deque<size_t> reachable_graphs_indexes_q;
+  // Insert main graph - with index zero
+  reachable_graphs_indexes_q.push_back(0);
+
+  while (reachable_graphs_indexes_q.empty() == false)
+  {
+    // Get first index from queue and remove it from queue
+    auto current_graph_index = reachable_graphs_indexes_q.front();
+    reachable_graphs_indexes_q.pop_front();
+
+    // If already check this graph - continue
+    if (reachable_indexes.find(current_graph_index) != reachable_indexes.end())
+      continue;
+
+    // Add current index to reachable set
+    reachable_indexes.insert(current_graph_index);
+
+    // Check current graph and add all graph indexes which can be reached from current graph
+    loco::Graph *graph = m->graph(current_graph_index);
+    assert(graph != nullptr);
+    checkGraph(graph, reachable_graphs_indexes_q);
+  }
+
+  assert(!reachable_indexes.empty());
+  // Let's remove all indexes which can not be reached from main graph
+  for (size_t i = 0; i < m->size(); ++i)
+  {
+    if (reachable_indexes.find(i) != reachable_indexes.end())
+      continue;
+
+    m->removeGraphByIndex(i);
+    changed = true;
+  }
+
+  return changed;
+}
+
+} // namespace luci