comaniac commented on a change in pull request #5134: [RELAY] Add 
MergeCompilerRegions pass
URL: https://github.com/apache/incubator-tvm/pull/5134#discussion_r398037445
 
 

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 File path: src/relay/transforms/merge_compiler_regions.cc
 ##########
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+/*
+ * 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/transforms/merge_compiler_regions.cc
+ *
+ * \brief After operators have been annotated with the targets that support
+ * them, this pass creates regions of the operators for each target. It
+ * is guaranteed that the regions will have a topological ordering so that
+ * no data dependency issues exist.
+ *
+ * This pass only introduces annotations to indicate the regions.
+ * partition_graph must subsequently be called to lift these regions out
+ * as external functions.
+ */
+
+#include <tvm/relay/analysis.h>
+#include <tvm/relay/attrs/annotation.h>
+#include <tvm/relay/expr.h>
+#include <tvm/ir/error.h>
+#include <tvm/relay/expr_functor.h>
+#include <tvm/relay/transform.h>
+
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include "../analysis/annotated_region_set.h"
+
+
+namespace tvm {
+namespace relay {
+namespace partitioning {
+
+// Cache compiler_begin and compiler_end annotation ops for equivalence check 
to
+// reduce registry lookup overhead.
+static const Op& compiler_begin_op = Op::Get("annotation.compiler_begin");
+static const Op& compiler_end_op = Op::Get("annotation.compiler_end");
+
+/*! \brief This is a pre-requisite pass to merge-supported pass.
+ *  The AnnotateRestDefault pass will put "default" Compiler Annotations to
+ *  nodes that are not annotated already. This is there to ensure that the
+ *  user will not leave un-annotated nodes MergeCompilerRegions pass is run.
+ *  Why? Because, MergeCompilerRegions pass assumes every node to be annotated.
+ */
+class AnnotateRestDefault : public ExprMutator {
+ public:
+  explicit AnnotateRestDefault(const Expr& expr) {
+      regions_ = AnnotatedRegionSet::Create(expr, compiler_begin_op, 
compiler_end_op);
+  }
+
+  Expr Annotate(const Expr& expr) {
+    // Its a function that is being passed on to annotate
+    func_ = Downcast<Function>(expr);
+
+    // Corner Case CC1 : If the last node does not belong
+    // to a region nede to add a compiler_end
+    auto region = regions_->GetRegion(func_->body);
+    auto mutated_expr = this->VisitExpr(expr);
+    if (!region.defined()) {
+      func_ = Downcast<Function>(mutated_expr);
+      // CC1 : add that compiler end after mutation
+      auto body = AddCompilerEnd_(func_->body);
+      func_ = Function(func_->params, body,
+                       body->checked_type_, {}, DictAttrs());
+      return Downcast<Expr>(func_);
+    } else {
+      return mutated_expr;
+    }
+  }
+
+  /*! \brief This function adds compiler ends to nodes that
+   * have a region AND they should not be arguments of the
+   * original function
+   * \param expr
+   * \return expr
+   */
+  Expr AddCompilerEnd(const Expr& expr) {
+    auto region = regions_->GetRegion(expr);
+    auto visited_expr = VisitExpr(expr);
+
+    // The compiler ends are added to nodes that does have a region
+    // AND they should not be arguments of the original function
+    if (!region.defined() &&
+       std::find(func_->params.begin(),
+                 func_->params.end(), visited_expr)
+                   == func_->params.end()) {
+      return AddCompilerEnd_(visited_expr);
+    } else {
+      return visited_expr;
+    }
+  }
+
+  Expr AddCompilerEnd_(const Expr& expr) {
+    const auto* end_op =
+      runtime::Registry::Get("relay.op.annotation._make.compiler_end");
+    CHECK(end_op);
+    Expr end = (*end_op)(expr, target_);
+    return end;
+  }
+
+  Expr VisitExpr_(const CallNode* call) final {
+    auto op_node = call->op.as<OpNode>();
+    auto ret = GetRef<Call>(call);
+
+    Array<Expr> args;
+
+    // Add compiler ends if the parent is supported
+    for (auto arg : call->args) {
+      args.push_back(AddCompilerEnd(arg));
+    }
+
+    if (op_node == nullptr || call->attrs.as<CompilerAttrs>() == nullptr) {
+      // Skip annotatation ops, only add default compiler to actual compute 
nodes
+
+      auto region = regions_->GetRegion(ret);
+      if (!region.defined()) {
+        // if the current node does not belong to annotated region
+        // annotate the all incoming edges (args)
+        // with "default" compile_begin and compiler_end annotations.
+        tvm::Array<tvm::relay::Expr> compiler_begins;
+        for (auto arg : args) {
+          const auto* begin_op =
+            runtime::Registry::Get("relay.op.annotation._make.compiler_begin");
+          CHECK(begin_op);
+          Expr begin = (*begin_op)(arg, target_);
+          compiler_begins.push_back(begin);
+        }
+        Expr update_call = Call(call->op, compiler_begins, call->attrs);
+        return update_call;
+      } else {
+        return Call(call->op, args, call->attrs);
+      }
+    } else {
+      return Call(call->op, args, call->attrs);
+    }
+  };
+
+  Expr VisitExpr_(const TupleNode *op) {
+    auto new_e = ExprMutator::VisitExpr_(op);
+    auto tup = Downcast<Tuple>(new_e);
+    Array<Expr> new_fields;
+    for (auto field : tup->fields) {
+      new_fields.push_back(AddCompilerEnd(field));
+    }
+    return Tuple(new_fields);
+  }
+
+  Expr VisitExpr_(const TupleGetItemNode *op) {
+    auto new_e = ExprMutator::VisitExpr_(op);
+    auto get = Downcast<TupleGetItem>(new_e);
+    return TupleGetItem(
+      AddCompilerEnd(get->tuple),
+      get->index);
+  }
+
+  Expr VisitExpr_(const LetNode *op) {
+    auto new_e = ExprMutator::VisitExpr_(op);
+    auto let = Downcast<Let>(new_e);
+    return Let(
+      let->var,
+      AddCompilerEnd(let->value),
+      AddCompilerEnd(let->body));
+  }
+
+  Expr VisitExpr_(const IfNode *op) {
+    auto new_e = ExprMutator::VisitExpr_(op);
+    auto iff = Downcast<If>(new_e);
+    return If(
+      AddCompilerEnd(iff->cond),
+      AddCompilerEnd(iff->true_branch),
+      AddCompilerEnd(iff->false_branch));
+  }
+
+  Expr VisitExpr_(const RefCreateNode *op) {
+    auto new_e = ExprMutator::VisitExpr_(op);
+    auto create = Downcast<RefCreate>(new_e);
+    return RefCreate(AddCompilerEnd(create->value));
+  }
+
+  Expr VisitExpr_(const RefReadNode *op) {
+    auto new_e = ExprMutator::VisitExpr_(op);
+    auto read = Downcast<RefRead>(new_e);
+    return RefRead(AddCompilerEnd(read->ref));
+  }
+
+  Expr VisitExpr_(const RefWriteNode *op) {
+    auto new_e = ExprMutator::VisitExpr_(op);
+    auto write = Downcast<RefWrite>(new_e);
+    return RefWriteNode::make(
+      AddCompilerEnd(write->ref),
+      AddCompilerEnd(write->value));
+  }
+
+ private:
+    AnnotatedRegionSet regions_;
+    const std::string target_ = "default";
+    Function func_;
+};
+
+class MergeAnnotations : public ExprMutator {
+ public:
+  explicit MergeAnnotations(AnnotatedRegionSet regions) : regions_(regions) {}
+
+  Expr VisitExpr_(const CallNode* call) final {
+    if (call->op == compiler_begin_op) {
+      if (call->args[0]->IsInstance<CallNode>()) {
+        auto arg = Downcast<Call>(call->args[0]);
+        if (arg->op == compiler_end_op) {
+          auto region1 = regions_->GetRegion(GetRef<Call>(call));
+          auto region2 = regions_->GetRegion(arg);
+          if (region1 == region2) {
+            return ExprMutator::VisitExpr(arg->args[0]);
+          }
+        }
+      }
+    }
+    return ExprMutator::VisitExpr_(call);
+  }
+
+ private:
+  AnnotatedRegionSet regions_;
+};
+
+class RegionMerger : public ExprVisitor {
+ public:
+  explicit RegionMerger(AnnotatedRegionSet regions) : regions_(regions) {}
+
+  void VisitExpr_(const CallNode* call) final {
+    if (call->op == compiler_end_op) {
+      auto region = regions_->GetRegion(GetRef<Call>(call));
+      // set the region target
+      auto compiler_attrs = call->attrs.as<CompilerAttrs>();
+      region_targets_[region->GetID()] = compiler_attrs->compiler;
+      std::vector<AnnotatedRegion> mergeable_regions;
+      // first look at the region args to determine the parent regions
+      for (const auto& arg : region->GetInputs()) {
+        // all args should be begin annotations
 
 Review comment:
   Add a CHECK to guarantee this assumption.

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