add more log and fix test_dist_base in multi_batch_merge_pass

paddle/fluid/framework/details/build_strategy.cc

@@ -177,11 +177,13 @@ std::unique_ptr<ir::Graph> BuildStrategy::Apply(
 #else
     const bool use_cuda) const {
 #endif
+  VLOG(3) << "apply all passes";
   // Create a default one if not finalized by user.
   CreatePassesFromStrategy(false);
 
   std::unique_ptr<ir::Graph> graph(new ir::Graph(main_program));
   for (std::shared_ptr<ir::Pass> &pass : pass_builder_->AllPasses()) {
+    VLOG(3) << "apply " << pass->Type();
     if (IsMultiDevPass(pass->Type())) {
       pass->Erase(kPlaces);
       pass->SetNotOwned<const std::vector<platform::Place>>(kPlaces, &places);

paddle/fluid/framework/ir/pass.cc

@@ -19,6 +19,7 @@ namespace paddle {
 namespace framework {
 namespace ir {
 std::unique_ptr<Graph> Pass::Apply(std::unique_ptr<Graph> graph) const {
+  VLOG(3) << "apply pass -> " << Type();
   PADDLE_ENFORCE(graph.get(), "graph passed to Pass::Apply() cannot be empty.");
   for (const std::string& attr : required_pass_attrs_) {
     PADDLE_ENFORCE(attrs_.find(attr) != attrs_.end(),

python/paddle/fluid/tests/unittests/test_dist_base.py

@@ -128,8 +128,7 @@ class TestDistRunnerBase(object):
 
         if args.batch_merge_repeat > 1:
             pass_builder = build_stra._finalize_strategy_and_create_passes()
-            mypass = pass_builder.insert_pass(
-                len(pass_builder.all_passes()) - 3, "multi_batch_merge_pass")
+            mypass = pass_builder.insert_pass(0, "multi_batch_merge_pass")
             mypass.set("num_repeats", args.batch_merge_repeat)
 
         if args.update_method == "nccl2":