junrushao1994 commented on a change in pull request #7765:
URL: https://github.com/apache/tvm/pull/7765#discussion_r608132415



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File path: include/tvm/tir/schedule/block_scope.h
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@@ -0,0 +1,249 @@
+/*
+ * 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 tvm/tir/schedule/block_scope.h
+ * \brief Definition of two pillar data structure for TensorIR scheduling: 
StmtSRef, BlockScope.
+ * \sa StmtSRefNode
+ * \sa BlockScopeNode
+ */
+#ifndef TVM_TIR_SCHEDULE_BLOCK_SCOPE_H_
+#define TVM_TIR_SCHEDULE_BLOCK_SCOPE_H_
+
+#include <tvm/tir/stmt.h>
+
+#include <unordered_map>
+
+namespace tvm {
+namespace tir {
+
+/*!
+ * \brief An object that refers to schedulable elements (block/for-loop) in 
TensorIR, aka "sref".
+ *
+ * Glossary
+ * - Block sref: An StmtSRef that points to a TensorIR block.
+ * - Loop sref: An StmtSRef that points to a TensorIR for loop.
+ * - Parent sref: The parent sref of an sref is the block/loop sref that 
points to its closest
+ * schedulable statement of its ancestors on the TensorIR AST.
+ * - Root sref: Sref to the root block. Every sref has exactly one parent sref 
except for root sref.
+ * - Sref tree: The parent-children-relationship of srefs that forms a tree, 
uniquely determined by
+ * the TensorIR AST.
+ */
+class StmtSRefNode : public Object {
+ public:
+  /*!
+   * \brief The block/for stmt the object refers to
+   * \note Non-owned reference (raw pointer) is used here, so that we can 
perform copy-on-write
+   * optimization on statements when possible. The strong reference is held in 
the ScheduleState.
+   */
+  const StmtNode* stmt;
+  /*! \brief The parent sref. */
+  StmtSRefNode* parent;
+  /*!
+   * \brief If the statement the sref points to is an element of a SeqStmt in 
the AST,
+   * then `seq_index` is set to its index; otherwise `seq_index` is -1
+   */
+  int64_t seq_index;

Review comment:
       Yeah I think both `int64_t` or `Optional<Integer>` works, and in this 
particular case where the API is not user-facing, to keep the overhead as low, 
let's go with the native int64_t :-)




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