Construct exec and ctx only once in cond op to speed up (#45794)

* Construct exec and ctx only once in cond op to speed up

* Fix construct function error

paddle/fluid/operators/controlflow/conditional_block_op.cc

@@ -21,6 +21,8 @@ limitations under the License. */
 #include "paddle/fluid/platform/mkldnn_helper.h"
 #endif
 
+DECLARE_bool(use_mkldnn);
+
 namespace paddle {
 namespace operators {
 
@@ -30,6 +32,9 @@ const char ConditionalOp::kCondition[] = "Cond";
 const char ConditionalOp::kScope[] = "Scope";
 const char ConditionalOp::kSkipEagerDeletionVars[] = "skip_eager_deletion_vars";
 
+using Executor = framework::Executor;
+using ExecutorPrepareContext = framework::ExecutorPrepareContext;
+
 class ConditionalBlockOp : public ConditionalOp {
  public:
   ConditionalBlockOp(const std::string &type,
@@ -76,22 +81,28 @@ class ConditionalBlockOp : public ConditionalOp {
       // Executors (executors declared inside control ops)
       platform::DontClearMKLDNNCache(dev_place);
 #endif
-      framework::Executor exec(dev_place);
       auto *block = Attr<framework::BlockDesc *>("sub_block");
       VLOG(3) << "Conditional block.idx = " << block->ID()
               << ", scope = " << &cur_scope;
       auto &skip_vars =
           Attr<std::vector<std::string>>(ConditionalOp::kSkipEagerDeletionVars);
-      exec.Run(*block->Program(),
-               &cur_scope,
-               block->ID(),
-               false,
-               true,
-               skip_vars,
-               /* force_disable_gc */ false,
-               /* keep_kid_scopes */ true);
+      if (!exec || !platform::is_same_place(exec->GetPlace(), dev_place)) {
+        auto &pdesc = *block->Program();
+        exec.reset(new Executor(dev_place));
+        if (FLAGS_use_mkldnn) exec->EnableMKLDNN(pdesc);
+        ctx = exec->Prepare(pdesc, block->ID(), skip_vars, false);
+#ifdef PADDLE_WITH_MKLDNN
+        platform::AttachPointerHashToMKLDNNKey(exec.get(), dev_place);
+        platform::RegisterModelLayout(ctx->ops_, dev_place);
+#endif
+      }
+      exec->RunPreparedContext(ctx.get(), &cur_scope, false, true, true);
     }
   }
+
+ private:
+  mutable std::shared_ptr<Executor> exec{nullptr};
+  mutable std::unique_ptr<ExecutorPrepareContext> ctx{nullptr};
 };
 
 class ConditionalBlockInferShape : public framework::InferShapeBase {
@@ -152,19 +163,21 @@ class ConditionalBlockGradOp : public ConditionalOp {
               scopes.size()));
       framework::Scope &cur_scope = *scopes[0];
 
-      framework::Executor exec(dev_place);
       auto *block = Attr<framework::BlockDesc *>("sub_block");
 
       VLOG(3) << "Conditional Grad block.idx = " << block->ID()
               << ", scope = " << &cur_scope;
-      exec.Run(*block->Program(),
-               &cur_scope,
-               block->ID(),
-               false,
-               true,
-               inside_grads,
-               /* force_disable_gc */ false,
-               /* keep_kid_scopes */ false);
+      if (!exec || !platform::is_same_place(exec->GetPlace(), dev_place)) {
+        auto &pdesc = *block->Program();
+        exec.reset(new Executor(dev_place));
+        if (FLAGS_use_mkldnn) exec->EnableMKLDNN(pdesc);
+        ctx = exec->Prepare(pdesc, block->ID(), inside_grads, false);
+#ifdef PADDLE_WITH_MKLDNN
+        platform::AttachPointerHashToMKLDNNKey(exec.get(), dev_place);
+        platform::RegisterModelLayout(ctx->ops_, dev_place);
+#endif
+      }
+      exec->RunPreparedContext(ctx.get(), &cur_scope, false, true, false);
 
       AssignLocalGradientToParentScope(
           dev_place, cur_scope, scope, inside_grads, outside_grads, inputs);
@@ -174,6 +187,10 @@ class ConditionalBlockGradOp : public ConditionalOp {
     AssignZeroToParentScope(dev_place, scope, inputs, outside_grads);
   }
 
+ private:
+  mutable std::shared_ptr<Executor> exec{nullptr};
+  mutable std::unique_ptr<ExecutorPrepareContext> ctx{nullptr};
+
  private:
   void AssignLocalGradientToParentScope(
       const platform::Place &place,