[Collage] SubGraphs (#11981)

* [Collage] SubGraphs

See https://github.com/apache/tvm-rfcs/blob/main/rfcs/0062-collage.md.

Collage works in units of 'sub-graphs', which are potential partitions of the
overall Relay model. This PR introduces SubGraph (an arbitrary partitioning, without
any implication about how it is to be represented), it's companion SubSubGraph
(implying a representation as a function), and some supporting odds 'n ends.

* - make Integer <-> size_t conversion explicit
- make 'Compiler' name explicit

* - fix namespace ambiguity

* - review comments

CMakeLists.txt

@@ -296,6 +296,7 @@ tvm_file_glob(GLOB_RECURSE RELAY_OP_SRCS
     )
 tvm_file_glob(GLOB_RECURSE RELAY_PASS_SRCS
     src/relay/analysis/*.cc
+    src/relay/collage/*.cc
     src/relay/transforms/*.cc
     src/relay/quantize/*.cc
     )

src/relay/collage/README.md

@@ -0,0 +1,26 @@
+<!--- Licensed to the Apache Software Foundation (ASF) under one -->
+<!--- or more contributor license agreements.  See the NOTICE file -->
+<!--- distributed with this work for additional information -->
+<!--- regarding copyright ownership.  The ASF licenses this file -->
+<!--- to you 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. -->
+
+The `CollagePartition` pass for finding optimal partitionings of Relay models.
+
+See the [RFC](https://github.com/mbs-octoml/mbs-tvm-rfcs/blob/mbs-rfcs-collage/rfcs/xxxx-collage.md).
+
+Based on:
+> *Collage: Automated Integration of Deep Learning Backends*  
+> Byungsoo Jeon, Sunghyun Park, Peiyuan Liao, Sheng Xu, Tianqi Chen, Zhihao Jia
+
+CAUTION: This is a prototype, do not use in prod.

src/relay/collage/dataflow_graph.cc

@@ -0,0 +1,48 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+/*!
+ * \file src/relay/collage/dataflow_graph.cc
+ * \brief A representation of the dataflow for an overall Relay expression.
+ */
+
+#include "./dataflow_graph.h"
+
+namespace tvm {
+namespace relay {
+namespace collage {
+
+DataflowGraph::DataflowGraph(Expr expr) : expr_(std::move(expr)) {
+  indexed_graph_ = CreateIndexedGraph(expr_);
+  downstream_map_.reserve(indexed_graph_->size());
+  for (PostDfsIndex index = 0; index < indexed_graph_->size(); ++index) {
+    const Node* node = indexed_graph_->index_to_node(index);
+    std::unordered_set<const Node*> downstream_nodes;
+    node->AccumulateDownstreamNodes(&downstream_nodes);
+    IndexSet index_set(indexed_graph_->size());
+    for (const Node* downstream_node : downstream_nodes) {
+      index_set.Add(downstream_node->index_);
+    }
+    downstream_map_.emplace_back(std::move(index_set));
+  }
+}
+
+}  // namespace collage
+}  // namespace relay
+}  // namespace tvm

src/relay/collage/dataflow_graph.h

@@ -0,0 +1,77 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+/*!
+ * \file src/relay/collage/dataflow_graph.h
+ * \brief A representation of the dataflow for an overall Relay expression.
+ */
+#ifndef TVM_RELAY_COLLAGE_DATAFLOW_GRAPH_H_
+#define TVM_RELAY_COLLAGE_DATAFLOW_GRAPH_H_
+
+#include <tvm/relay/expr.h>
+
+#include <memory>
+#include <vector>
+
+#include "../ir/indexed_graph.h"
+#include "./index_set.h"
+
+namespace tvm {
+namespace relay {
+namespace collage {
+
+/*!
+ * \brief Represents the dataflow of an overall Relay expression.
+ */
+class DataflowGraph {
+ public:
+  using Node = IndexedGraph<Expr>::Node;
+
+  explicit DataflowGraph(Expr expr);
+
+  size_t size() const { return indexed_graph_->size(); }
+  const Node* index_to_node(PostDfsIndex index) const {
+    return indexed_graph_->index_to_node(index);
+  }
+  const Node* item_to_node(const Expr& expr) const { return indexed_graph_->item_to_node(expr); }
+  const Node* item_to_node(const ExprNode* expr_node) const {
+    return indexed_graph_->item_to_node(expr_node);
+  }
+  const Expr& expr() const { return expr_; }
+  const IndexedGraph<Expr>& indexed_graph() const { return *indexed_graph_; }
+
+  const IndexSet& downstream_of(PostDfsIndex index) const {
+    ICHECK_LT(index, indexed_graph_->size());
+    return downstream_map_[index];
+  }
+
+ private:
+  /*! \brief The overall expression. */
+  Expr expr_;
+  /*! \brief The indexed graph which captures the main dataflow. */
+  std::unique_ptr<IndexedGraph<Expr>> indexed_graph_;
+  /*! \brief Map from a node's PostDfsIndex to the set of its downstream dataflow node indexes. */
+  std::vector<IndexSet> downstream_map_;
+};
+
+}  // namespace collage
+}  // namespace relay
+}  // namespace tvm
+
+#endif  // TVM_RELAY_COLLAGE_DATAFLOW_GRAPH_H_

src/relay/collage/index_set.cc

@@ -0,0 +1,231 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+/*!
+ * \file src/relay/collage/index_set.cc
+ * \brief Efficient representation of a set of post-dfs indexes.
+ */
+
+#include "./index_set.h"
+
+namespace tvm {
+namespace relay {
+namespace collage {
+
+// TODO(mbs): These should operate one-word-at-a-time
+
+IndexSet::IndexSet(size_t size, const std::vector<size_t>& indexes) : bitvec_(size, false) {
+  for (size_t index : indexes) {
+    ICHECK_LT(index, bitvec_.size());
+    ICHECK(!bitvec_[index]);
+    bitvec_[index] = true;
+  }
+}
+
+IndexSet IndexSet::operator&(const IndexSet& that) const {
+  ICHECK_EQ(bitvec_.size(), that.bitvec_.size());
+  std::vector<bool> result(bitvec_.size(), false);
+  for (size_t index = 0; index < bitvec_.size(); ++index) {
+    result[index] = bitvec_[index] && that.bitvec_[index];
+  }
+  return IndexSet(result);
+}
+
+IndexSet IndexSet::operator|(const IndexSet& that) const {
+  ICHECK_EQ(bitvec_.size(), that.bitvec_.size());
+  std::vector<bool> result(bitvec_.size(), false);
+  for (size_t index = 0; index < bitvec_.size(); ++index) {
+    result[index] = bitvec_[index] || that.bitvec_[index];
+  }
+  return IndexSet(result);
+}
+
+IndexSet IndexSet::operator-(const IndexSet& that) const {
+  ICHECK_EQ(bitvec_.size(), that.bitvec_.size());
+  std::vector<bool> result(bitvec_.size());
+  for (size_t index = 0; index < bitvec_.size(); ++index) {
+    result[index] = bitvec_[index] && !that.bitvec_[index];
+  }
+  return IndexSet(result);
+}
+
+bool IndexSet::AreDisjoint(const IndexSet& that) const {
+  ICHECK_EQ(bitvec_.size(), that.bitvec_.size());
+  for (size_t index = 0; index < bitvec_.size(); index++) {
+    if (bitvec_[index] && that.bitvec_[index]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool IndexSet::IsSubset(const IndexSet& that) const {
+  ICHECK_EQ(bitvec_.size(), that.bitvec_.size());
+  for (size_t index = 0; index < bitvec_.size(); index++) {
+    if (bitvec_[index] && !that.bitvec_[index]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool IndexSet::Intersects(const IndexSet& that) const {
+  ICHECK_EQ(bitvec_.size(), that.bitvec_.size());
+  for (size_t index = 0; index < bitvec_.size(); index++) {
+    if (bitvec_[index] && that.bitvec_[index]) {
+      return true;
+    }
+  }
+  return false;
+}
+
+IndexSet IndexSet::Subst(size_t new_size, const IndexSubst& subst) const {
+  std::vector<bool> result(new_size, false);
+  for (PostDfsIndex index = 0; index < bitvec_.size(); ++index) {
+    if (!bitvec_[index]) {
+      continue;
+    }
+    auto itr = subst.find(index);
+    ICHECK(itr != subst.end());
+    PostDfsIndex new_index = itr->second;
+    ICHECK(new_index < new_size);
+    ICHECK(!result[new_index]);
+    result[new_index] = true;
+  }
+  return IndexSet(result);
+}
+
+size_t IndexSet::PopCount() const {
+  size_t n = 0;
+  for (size_t index = 0; index < bitvec_.size(); index++) {
+    if (bitvec_[index]) {
+      ++n;
+    }
+  }
+  return n;
+}
+
+bool IndexSet::IsZero() const {
+  for (size_t index = 0; index < bitvec_.size(); index++) {
+    if (bitvec_[index]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+size_t IndexSet::FirstInsideIndex() const {
+  for (size_t index = 0; index < bitvec_.size(); index++) {
+    if (bitvec_[index]) {
+      return index;
+    }
+  }
+  return bitvec_.size();
+}
+
+size_t IndexSet::LastInsideIndex() const {
+  for (size_t i = bitvec_.size(); i > 0; i--) {
+    const size_t index = i - 1;
+    if (bitvec_[index]) {
+      return index;
+    }
+  }
+  return bitvec_.size();
+}
+
+size_t IndexSet::NextIndex(size_t index) const {
+  ICHECK_LT(index, bitvec_.size());
+  for (index++; index < bitvec_.size(); index++) {
+    if (bitvec_[index]) {
+      return index;
+    }
+  }
+  return bitvec_.size();
+}
+
+size_t IndexSet::FirstOutsideIndex() const {
+  for (size_t index = 0; index < bitvec_.size(); index++) {
+    if (!bitvec_[index]) {
+      return index;
+    }
+  }
+  return bitvec_.size();
+}
+
+bool IndexSet::operator==(const IndexSet& that) const {
+  ICHECK_EQ(bitvec_.size(), that.bitvec_.size());
+  return bitvec_ == that.bitvec_;
+}
+
+bool IndexSet::operator!=(const IndexSet& that) const {
+  ICHECK_EQ(bitvec_.size(), that.bitvec_.size());
+  return bitvec_ != that.bitvec_;
+}
+
+bool IndexSet::operator<(const IndexSet& that) const {
+  ICHECK_EQ(bitvec_.size(), that.bitvec_.size());
+  for (size_t index = 0; index < bitvec_.size(); index++) {
+    if (bitvec_[index] && !that.bitvec_[index]) {
+      return true;
+    }
+    if (!bitvec_[index] && that.bitvec_[index]) {
+      return false;
+    }
+  }
+  return false;
+}
+
+size_t IndexSet::hash() const {
+  std::hash<std::vector<bool>> h;
+  return h(bitvec_);
+}
+
+std::string IndexSet::ToString() const {
+  std::ostringstream os;
+  os << "{";
+  bool first = true;
+  for (size_t start = 0; start < bitvec_.size(); /*no-op*/) {
+    if (!bitvec_[start]) {
+      ++start;
+      continue;
+    }
+    size_t end;
+    for (end = start + 1; end < bitvec_.size() && bitvec_[end]; ++end) {
+      /*no-op*/
+    }
+    if (first) {
+      first = false;
+    } else {
+      os << ",";
+    }
+    os << start;
+    if (end > start + 2) {
+      os << ".." << (end - 1);
+      start = end;
+    } else {
+      ++start;
+    }
+  }
+  os << "}";
+  return os.str();
+}
+
+}  // namespace collage
+}  // namespace relay
+}  // namespace tvm