[TIR][USMP] Greedy algorithms for USMP

This commit implements greedy algorithms for
USMP based on size and number of liveness
conflicts.

* This includes a slight fix for buffer info
  extraction where non-linear network buffers
  owned by the main function should not show
  sporadic liveness.

Change-Id: I957d543e75b3b0bcf5fc1fbc7870705c875c7a03

Author: manupak

src/tir/usmp/algo/greedy.cc

@@ -0,0 +1,235 @@
+/*
+ * 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 tir/analysis/usmp/algo/greedy_by_size.cc
+ * \brief This source contains greedy algorithms for planning
+ * memory for USMP. There are two algorithms present here :
+ * 1) greedy_by_size and 2) greedy_by_conflicts.
+ *
+ * greedy_by_size : this algorithm prioritizes placing the
+ * largest size buffer to the given pools. The BufferInfo objects
+ * are sorted based on the size and placed on each pool adhering
+ * to size_hint constraint.
+ *
+ * greedy_by_conflicts : this algorithm prioritizes placing the
+ * the most liveness conflicted buffer to the given pools. The
+ * BufferInfo objects are sorted based on the number of conflicts
+ * and placed on each pool adhering to size_hint constraint.
+ */
+
+#include <tvm/arith/analyzer.h>
+#include <tvm/runtime/device_api.h>
+#include <tvm/tir/builtin.h>
+#include <tvm/tir/function.h>
+#include <tvm/tir/stmt_functor.h>
+#include <tvm/tir/usmp/utils.h>
+
+namespace tvm {
+namespace tir {
+namespace usmp {
+namespace algo {
+
+/*!
+ * \brief This is the base class for Greedy Algorithms where the sorting
+ * is specialized in the extended classes based on the greedy criteria.
+ */
+class GreedyBase {
+ public:
+  GreedyBase() {}
+  /*!
+   * \brief This function should be implemented by the extended classes to sort the BufferInfo
+   * objects based on a criteria and then calling PostSortAllocation.
+   */
+  virtual Map<BufferInfo, PoolAllocation> PlanMemory(const Array<BufferInfo>& buffer_info_arr) = 0;
+
+ protected:
+  /*!
+   * \brief Rounds up the offset to satisfy the alignement requirement
+   */
+  size_t round_up_to_byte_alignment(const size_t& non_aligned_byte_offset,
+                                    const int& byte_alignment) {
+    return ((non_aligned_byte_offset + byte_alignment - 1) / byte_alignment) * byte_alignment;
+  }
+
+  /*!
+   * \brief A helper function check whether a offset is valid given the constraints
+   */
+  bool IsValidPlacement(const PoolInfo& candidate_pool, const size_t& next_offset,
+                        const size_t& size_bytes) {
+    if (candidate_pool->size_hint_bytes == -1) {
+      // this means pool is not bounded
+      return true;
+    }
+    auto pool_size = static_cast<size_t>(candidate_pool->size_hint_bytes->value);
+    auto max_address = next_offset + size_bytes;
+    if (max_address <= pool_size) {
+      return true;
+    }
+    return false;
+  }
+
+  /*!
+   * \brief Selects a pool for placement in the given set of ordered pool candidates
+   */
+  PoolInfo SelectPlacementPool(
+      const Array<PoolInfo>& pool_candidates,
+      const std::unordered_map<PoolInfo, size_t, ObjectPtrHash, ObjectPtrEqual>& pool_offsets) {
+    // Here the pool candidates are ordered when it is consumed by the algorithm.
+    // This could be from order the user has specified. However, schedulers are
+    // welcome to change the order for performance reasons.
+    for (const auto& pool_info : pool_candidates) {
+      if (pool_offsets.count(pool_info)) {
+        return pool_info;
+      }
+    }
+    ICHECK(false) << "TVM USMP Internal Error: no candidate have been selected!";
+    return PoolInfo();
+  }
+
+  /*!
+   * \brief This is the base allocation function that works on sorted BufferInfo objects based
+   * on the greedy heuristic. The sorting algorithm has to be called before calling this.
+   */
+  Map<BufferInfo, PoolAllocation> PostSortAllocation(
+      const std::vector<BufferInfo>& buffer_info_vec) {
+    Map<BufferInfo, PoolAllocation> pool_allocations;
+    for (const auto& buf_info : buffer_info_vec) {
+      std::unordered_map<PoolInfo, size_t, ObjectPtrHash, ObjectPtrEqual> pool_offset_candidates;
+      for (const auto& pool_info : buf_info->pool_candidates) {
+        // Mark pool candidates that satisfy the size constraints.
+        if (IsValidPlacement(pool_info, 0, buf_info->size_bytes->value)) {
+          pool_offset_candidates[pool_info] = 0;
+        }
+      }
+
+      for (const auto& conflict_buf_info_obj : buf_info->conflicts) {
+        auto conflict_buf_info = Downcast<BufferInfo>(conflict_buf_info_obj);
+        size_t next_offset = 0;
+        // We only look at already allocated BufferInfo in-terms of conflicts.
+        if (pool_allocations.count(conflict_buf_info)) {
+          auto pool_allocation = pool_allocations[conflict_buf_info];
+          next_offset = pool_allocation->byte_offset + conflict_buf_info->size_bytes;
+          next_offset =
+              round_up_to_byte_alignment(next_offset, conflict_buf_info->alignment->value);
+          // Checks whether the next offset in the same pool as the conflicting BufferInfo is valid.
+          if (IsValidPlacement(pool_allocation->pool_info, next_offset,
+                               buf_info->size_bytes->value)) {
+            // There could be multiple conflicting BufferInfo in the same pool.
+            // Thus, we need to make sure we pick the largest offset of them all.
+            if (next_offset > pool_offset_candidates[pool_allocation->pool_info]) {
+              pool_offset_candidates[pool_allocation->pool_info] = next_offset;
+            }
+          } else {
+            pool_offset_candidates.erase(pool_allocation->pool_info);
+          }
+        }
+      }
+      auto selected_pool = SelectPlacementPool(buf_info->pool_candidates, pool_offset_candidates);
+      pool_allocations.Set(
+          buf_info, PoolAllocation(selected_pool, Integer(pool_offset_candidates[selected_pool])));
+    }
+    return pool_allocations;
+  }
+};
+
+/*!
+ * \brief This class implements Greedy by the size of BufferInfo
+ * greedy algorithm. Please refer to main documentation of the file
+ * for more details.
+ */
+class GreedySize : public GreedyBase {
+ public:
+  GreedySize() {}
+  Map<BufferInfo, PoolAllocation> PlanMemory(const Array<BufferInfo>& buffer_info_arr) {
+    std::vector<BufferInfo> buffer_info_vec;
+    Map<BufferInfo, PoolAllocation> pool_allocations;
+    for (const auto& buffer_info : buffer_info_arr) {
+      buffer_info_vec.push_back(std::move(buffer_info));
+    }
+    std::sort(buffer_info_vec.begin(), buffer_info_vec.end(),
+              [](const BufferInfo& a, const BufferInfo& b) {
+                if (a->size_bytes->value == b->size_bytes->value) {
+                  if (a->conflicts.size() == b->conflicts.size()) {
+                    auto a_name_hash = std::hash<std::string>{}(a->name_hint->data);
+                    auto b_name_hash = std::hash<std::string>{}(b->name_hint->data);
+                    return a_name_hash > b_name_hash;
+                  } else {
+                    return a->conflicts.size() > b->conflicts.size();
+                  }
+                }
+                return a->size_bytes > b->size_bytes;
+              });
+    return PostSortAllocation(buffer_info_vec);
+  }
+};
+
+/*!
+ * \brief This class implements Greedy by the number of conflicts of
+ * BufferInfo greedy algorithm. Please refer to main documentation
+ * of the file for more details.
+ */
+class GreedyConflicts : public GreedyBase {
+ public:
+  GreedyConflicts() {}
+  Map<BufferInfo, PoolAllocation> PlanMemory(const Array<BufferInfo>& buffer_info_arr) {
+    std::vector<BufferInfo> buffer_info_vec;
+    Map<BufferInfo, PoolAllocation> pool_allocations;
+    for (const auto& buffer_info : buffer_info_arr) {
+      buffer_info_vec.push_back(std::move(buffer_info));
+    }
+    std::sort(buffer_info_vec.begin(), buffer_info_vec.end(),
+              [](const BufferInfo& a, const BufferInfo& b) {
+                if (a->conflicts.size() == b->conflicts.size()) {
+                  if (a->size_bytes->value == b->size_bytes->value) {
+                    auto a_name_hash = std::hash<std::string>{}(a->name_hint->data);
+                    auto b_name_hash = std::hash<std::string>{}(b->name_hint->data);
+                    return a_name_hash > b_name_hash;
+                  } else {
+                    return a->size_bytes->value > b->size_bytes->value;
+                  }
+                }
+                return a->conflicts.size() > b->conflicts.size();
+              });
+    return PostSortAllocation(buffer_info_vec);
+  }
+};
+
+Map<BufferInfo, PoolAllocation> GreedyBySize(const Array<BufferInfo>& buffer_info_arr) {
+  return GreedySize().PlanMemory(buffer_info_arr);
+}
+
+Map<BufferInfo, PoolAllocation> GreedyByConflicts(const Array<BufferInfo>& buffer_info_arr) {
+  return GreedyConflicts().PlanMemory(buffer_info_arr);
+}
+
+TVM_REGISTER_GLOBAL("tir.usmp.algo.greedy_by_size")
+    .set_body_typed([](Array<BufferInfo> buffer_info_arr) {
+      return GreedyBySize(buffer_info_arr);
+    });
+
+TVM_REGISTER_GLOBAL("tir.usmp.algo.greedy_by_conflicts")
+    .set_body_typed([](Array<BufferInfo> buffer_info_arr) {
+      return GreedyByConflicts(buffer_info_arr);
+    });
+
+}  // namespace algo
+}  // namespace usmp
+}  // namespace tir
+}  // namespace tvm