[PASS] Improve graph fusion (#286)

* [PASS] Improve graph fusion

* Change fusion center to segment head

* Use 'master' to identity the schedule node

* Make things compact

* Fix

apps/graph_executor/src/graph_pass.cc

@@ -21,7 +21,7 @@ using nnvm::IndexedGraph;
 // The single fuse rule.
 enum class FuseRule {
   kUknown,
-  kFuseToParent,
+  kFuseToMaster,
   kRealize
 };
 
@@ -57,10 +57,16 @@ nnvm::Graph GraphPartition(nnvm::Graph g) {
       ++ref_count[e.node_id];
     }
   }
+  for (const auto& e : idx.outputs()) {
+    // this line will realize all the outputs
+    ref_count[e.node_id] += 2;
+  }
   // Pattern fo the subgraph
   std::vector<TOpPattern> pattern_vec(idx.num_nodes(),  kExtern);
   // Whether node can be fused to parent.
   std::vector<FuseRule> fuse_vec(idx.num_nodes(), FuseRule::kUknown);
+  // Master node id of fusion segment.
+  std::vector<int> master_vec(idx.num_nodes(), -1);
   // Operator pattern
   static auto& op_pattern = nnvm::Op::GetAttr<TOpPattern>("TOpPattern");
 
@@ -70,38 +76,58 @@ nnvm::Graph GraphPartition(nnvm::Graph g) {
       fuse_vec[nid] = FuseRule::kRealize; continue;
     }
     TOpPattern pt = op_pattern.get(inode.source->op(), kExtern);
+
     if (pt <= kBroadcast) {
-      // Looking for fusable bcast pattern
+      int chosen_master = -1;
       bool ewise = inode.source->num_outputs() == 1;
       for (const auto& e : inode.inputs) {
         if (fuse_vec[e.node_id] == FuseRule::kUknown) {
-          if (pattern_vec[e.node_id] == kBroadcast) {
-            ewise = false;
-            fuse_vec[e.node_id] = FuseRule::kFuseToParent;
-          } else if (pattern_vec[e.node_id] == kElemWise) {
-            fuse_vec[e.node_id] = FuseRule::kFuseToParent;
+          TOpPattern ipt = pattern_vec[e.node_id];
+          if (ipt != kElemWise) ewise = false;
+          if (ipt <= kBroadcast) {
+            fuse_vec[e.node_id] = FuseRule::kFuseToMaster;
+          } else if (ipt == kComplex && chosen_master == -1 &&
+            shape_vec[idx.entry_id(nid, 0)] == shape_vec[idx.entry_id(e)]) {
+            chosen_master = master_vec[e.node_id];
+            fuse_vec[e.node_id] = FuseRule::kFuseToMaster;
+          } else {
+            fuse_vec[e.node_id] = FuseRule::kRealize;
           }
         }
         if (ewise) {
-          TShape oshape = shape_vec[idx.entry_id(nid, 0)];
-          if (oshape != shape_vec[idx.entry_id(e)]) ewise = false;
+          if (shape_vec[idx.entry_id(nid, 0)] != shape_vec[idx.entry_id(e)]) {
+            ewise = false;
+          }
         }
       }
-      pt = ewise ? kElemWise : kBroadcast;
-    } else if (pt == kComplex) {
+      master_vec[nid] = chosen_master;
+      if (chosen_master != -1) {
+        pt = kComplex;
+      } else {
+        pt = ewise ? kElemWise : kBroadcast;
+      }
+    } else {
+      master_vec[nid] = nid;
       for (const auto& e : inode.inputs) {
         if (fuse_vec[e.node_id] == FuseRule::kUknown) {
-          if (pattern_vec[e.node_id] <= kBroadcast) {
-            fuse_vec[e.node_id] = FuseRule::kFuseToParent;
+          fuse_vec[e.node_id] = FuseRule::kRealize;
+          if (master_vec[e.node_id] == -1) {
+            master_vec[e.node_id] = e.node_id;
           }
         }
       }
     }
+
     pattern_vec[nid] = pt;
     if (ref_count[nid] > 1) {
       fuse_vec[nid] = FuseRule::kRealize;
+      if (master_vec[nid] == -1) {
+        master_vec[nid] = nid;
+      }
     }
   }
+
+
   // point to the group root id of each node
   std::vector<int> group_vec(idx.num_nodes(), -1);
   for (uint32_t i = idx.num_nodes(); i != 0; --i) {
@@ -112,14 +138,15 @@ nnvm::Graph GraphPartition(nnvm::Graph g) {
     }
     // propagate the group id.
     for (const auto& e : inode.inputs) {
-      if (fuse_vec[e.node_id] == FuseRule::kFuseToParent) {
+      if (fuse_vec[e.node_id] == FuseRule::kFuseToMaster) {
         CHECK(group_vec[e.node_id] == -1||
               group_vec[e.node_id] == group_vec[nid]);
         group_vec[e.node_id] = group_vec[nid];
       }
     }
   }
   g.attrs["group_root"] = std::make_shared<any>(std::move(group_vec));
+  g.attrs["group_master"] = std::make_shared<any>(std::move(master_vec));
   g.attrs["pattern"] = std::make_shared<any>(std::move(pattern_vec));
   g.attrs["dltype"] = std::make_shared<any>(std::move(dltype_vec));
   return g;
@@ -172,6 +199,7 @@ nnvm::Graph GraphFuse(nnvm::Graph g) {
   const DLTypeVector& dltype_vec = g.GetAttr<DLTypeVector>("dltype");
   const DTypeVector& dtype_vec = g.GetAttr<DTypeVector>("dtype");
   const std::vector<int>& group_vec = g.GetAttr<std::vector<int> >("group_root");
+  const std::vector<int>& master_vec = g.GetAttr<std::vector<int> >("group_master");
   const std::vector<TOpPattern>& pattern_vec =
       g.GetAttr<std::vector<TOpPattern> >("pattern");
   std::string target = g.GetAttr<std::string>("target");
@@ -239,15 +267,18 @@ nnvm::Graph GraphFuse(nnvm::Graph g) {
     Array<Tensor> out = fcompute[inode.source->op()](
         inode.source->attrs, inputs);
     CHECK_EQ(out.size(), inode.source->num_outputs());
+
+    // schedule on root node, and use master's schedule
     if (nid != root_id) {
       for (uint32_t index = 0; index < inode.source->num_outputs(); ++index) {
         uint32_t eid = idx.entry_id(nid, index);
         tensor_vec[eid] = out[index];
       }
     } else {
-      // Work on schedule
       fe.outputs = out;
-      fe.schedule = fschedule[inode.source->op()](
+      int master = master_vec[root_id];
+      CHECK_GE(master, 0);
+      fe.schedule = fschedule[idx[master].source->op()](
           inode.source->attrs, fe.outputs, target);
       std::ostringstream os;
       os << inode.source->attrs.name + "_id" << nid;
@@ -307,10 +338,12 @@ nnvm::Graph GraphFuse(nnvm::Graph g) {
       old_new[nid] = np;
     }
   }
+
   nnvm::Graph ret;
   for (const auto& e : idx.outputs()) {
-    auto it = old_new.find(e.node_id);
-    CHECK(it != old_new.end());
+    auto it = old_new.find(group_vec[e.node_id]);
+    CHECK(it != old_new.end())
+        << "cannot find node_id=" << e.node_id;
     ret.outputs.emplace_back(
         nnvm::NodeEntry{it->second, e.index, e.version});
   }