add SwitchDeadBranchElimination & MergePass in graph prepare

ge/graph/preprocess/graph_preprocess.cc

@@ -1740,6 +1740,8 @@ Status GraphPrepare::PrepareOptimize() {
   IdentityPass identity_pass(false);
   AssignPass assign_pass;
   SnapshotPass snapshot_pass;
+  SwitchDeadBranchElimination switch_dead_branch_elimination;
+  MergePass merge_pass;
   if (!options_.train_graph_flag) {
     names_to_passes.emplace_back("DropOutPass", &dropout_pass);
     names_to_passes.emplace_back("AssertPass", &assert_pass);
@@ -1753,6 +1755,8 @@ Status GraphPrepare::PrepareOptimize() {
   names_to_passes.emplace_back("VarIsInitializedOpPass", &var_is_initialized_pass);
   names_to_passes.emplace_back("ParallelConcatStartOpPass", &parallel_concat_start_op_pass);
   names_to_passes.emplace_back("IdentityPass", &identity_pass);
+  names_to_passes.emplace_back("SwitchDeadBranchElimination", &switch_dead_branch_elimination);
+  names_to_passes.emplace_back("MergePass", &merge_pass);
   if (GetContext().GetHostExecFlag()) {
     names_to_passes.emplace_back("AssignPass", &assign_pass);
   }