Simplify DataStructure in SSAGraph

paddle/fluid/framework/details/multi_devices_graph_builder.cc

@@ -59,7 +59,11 @@ std::unique_ptr<SSAGraph> MultiDevSSAGraphBuilder::Build(
   auto graph = new SSAGraph();
   SSAGraph &result = *graph;
   std::unordered_set<std::string> og_has_been_broadcast;
-  result.vars_.resize(places_.size());
+
+  // We cannot invoke resize. It is a bug of GCC 4.8
+  result.vars_ = std::vector<
+      std::unordered_map<std::string, std::vector<std::unique_ptr<VarHandle>>>>(
+      places_.size());
 
   bool is_forwarding = true;
   for (auto *op : program.Block(0).AllOps()) {
@@ -147,15 +151,16 @@ std::unique_ptr<SSAGraph> MultiDevSSAGraphBuilder::Build(
             if (vars.empty()) {  // This device has no data. continue.
               continue;
             }
-            auto *prev_grad = &vars[vars.size() - 1];
-            op_handle->AddInput(prev_grad);
+            auto &prev_grad = vars[vars.size() - 1];
+            op_handle->AddInput(prev_grad.get());
 
-            auto &var = vars[vars.size()];
-            var.place_ = p;
-            var.name_ = og;
-            var.version_ = vars.size() - 1;
+            vars.emplace_back(new VarHandle);
+            auto &var = vars.back();
+            var->place_ = p;
+            var->name_ = og;
+            var->version_ = vars.size() - 1;
 
-            op_handle->AddOutput(&var);
+            op_handle->AddOutput(var.get());
           }
 #else
           PADDLE_ENFORCE("Not implemented");

paddle/fluid/framework/details/ssa_graph.h

@@ -16,6 +16,8 @@
 
 #include <map>
 #include <string>
+#include <vector>
+
 #include "paddle/fluid/framework/details/op_handle_base.h"
 #include "paddle/fluid/framework/details/var_handle.h"
 
@@ -24,7 +26,9 @@ namespace framework {
 namespace details {
 
 struct SSAGraph {
-  std::vector<std::unordered_map<std::string, std::map<int, VarHandle>>> vars_;
+  std::vector<
+      std::unordered_map<std::string, std::vector<std::unique_ptr<VarHandle>>>>
+      vars_;
   // aux variables to represent dependency. Useful to resolve data hazard.
   std::unordered_set<std::unique_ptr<VarHandleBase>> dep_vars_;
   std::vector<std::unique_ptr<OpHandleBase>> ops_;

paddle/fluid/framework/details/ssa_graph_builder.cc

@@ -27,8 +27,8 @@ void SSAGraphBuilder::PolishGraphToSupportDataHazards(SSAGraph *graph) {
       auto it_old = name_pair.second.rbegin();
       ++it_old;
       for (; it_old != name_pair.second.rend(); it_new = it_old, ++it_old) {
-        auto *write_op = it_new->second.generated_op_;
-        auto &read_ops = it_old->second.pending_ops_;
+        auto *write_op = (*it_new)->generated_op_;
+        auto &read_ops = (*it_old)->pending_ops_;
 
         for (auto *read_op : read_ops) {
           // Manually add a dependency var from read_op to write_op;
@@ -54,14 +54,15 @@ VarHandle *SSAGraphBuilder::CreateOrGetLatestVarHandle(
   auto &var_holder = var_holders[each_var_name];
   VarHandle *var = nullptr;
   if (var_holder.empty()) {
+    var_holder.emplace_back(new VarHandle);
     auto &init_var = var_holder[0];
-    init_var.place_ = place;
-    init_var.name_ = each_var_name;
-    init_var.generated_op_ = nullptr;
-    init_var.version_ = 0;
-    var = &init_var;
+    init_var->place_ = place;
+    init_var->name_ = each_var_name;
+    init_var->generated_op_ = nullptr;
+    init_var->version_ = 0;
+    var = init_var.get();
   } else {
-    var = &var_holder.rbegin()->second;
+    var = var_holder.rbegin()->get();
   }
   return var;
 }
@@ -72,19 +73,20 @@ void SSAGraphBuilder::CreateOpOutput(SSAGraph *graph, OpHandleBase *op_handle,
                                      size_t place_offset) {
   auto &vars = graph->vars_[place_offset][each_var_name];
   size_t version = vars.size();
-  auto &var = vars[version];
-  var.version_ = version;
-  var.name_ = each_var_name;
-  var.place_ = place;
-  op_handle->AddOutput(&var);
+  vars.emplace_back(new VarHandle());
+  auto &var = vars.back();
+  var->version_ = version;
+  var->name_ = each_var_name;
+  var->place_ = place;
+  op_handle->AddOutput(var.get());
 }
 
 template <typename Callback>
 void IterAllVar(const SSAGraph &graph, Callback callback) {
   for (auto &each : graph.vars_) {
     for (auto &pair1 : each) {
       for (auto &pair2 : pair1.second) {
-        callback(pair2.second);
+        callback(*pair2);
       }
     }
   }

paddle/fluid/framework/details/threaded_ssa_graph_executor.cc

@@ -69,7 +69,7 @@ FeedFetchList ThreadedSSAGraphExecutor::Run(
   for (auto &var_map : graph_->vars_) {
     for (auto &name_pair : var_map) {
       for (auto &version_pair : name_pair.second) {
-        InsertPendingVar(version_pair.second);
+        InsertPendingVar(*version_pair);
       }
     }
   }
@@ -95,7 +95,7 @@ FeedFetchList ThreadedSSAGraphExecutor::Run(
     for (auto &var_map : graph_->vars_) {
       auto it = var_map.find(fetch_var_name);
       if (it != var_map.end()) {
-        fetched_vars[fetch_var_name].push_back(&it->second.rbegin()->second);
+        fetched_vars[fetch_var_name].push_back(it->second.rbegin()->get());
       }
     }
   }