Optimize while_op when is_test is true. (#15811)

test=develop

paddle/fluid/framework/lod_rank_table.cc

@@ -19,6 +19,10 @@ namespace framework {
 void LoDRankTable::Reset(const LoD& lod, size_t level) {
   this->coarse_lod_.clear();
   this->items_.clear();
+  if (lod.size() == 0) {
+    // Reset to a empty rank table.
+    return;
+  }
   PADDLE_ENFORCE(level < lod.size(),
                  "Cannot rank lod since the level %d is less than lod size %d",
                  level, lod.size());

paddle/fluid/operators/controlflow/while_op.cc

@@ -58,6 +58,7 @@ class WhileOp : public framework::OperatorBase {
   void RunImpl(const framework::Scope &scope,
                const platform::Place &dev_place) const override {
     PADDLE_ENFORCE_NOT_NULL(scope.FindVar(Input(kCondition)));
+
     auto &cond = scope.FindVar(Input(kCondition))->Get<LoDTensor>();
     PADDLE_ENFORCE_EQ(cond.dims(), paddle::framework::make_ddim({1}));
 
@@ -77,13 +78,33 @@ class WhileOp : public framework::OperatorBase {
     VLOG(2) << GetSkipEagerDeletionVarsDebugString(skip_vars);
 
     auto ctx = executor.Prepare(*program, block->ID(), skip_vars);
+    if (!is_test) {
       while (cond.data<bool>()[0]) {
         auto &current_scope = scope.NewScope();
         step_scopes->push_back(&current_scope);
-      executor.RunPreparedContext(ctx.get(), &current_scope, false, true, true);
-      if (is_test) {
-        scope.DeleteScope(&current_scope);
+        executor.RunPreparedContext(ctx.get(), &current_scope, false, true,
+                                    true);
+      }
+    } else {
+      auto &current_scope = scope.NewScope();
+      executor.CreateVariables(*program, &current_scope, block->ID());
+      while (cond.data<bool>()[0]) {
+        for (auto &name : current_scope.LocalVarNames()) {
+          auto *var = current_scope.Var(name);
+          framework::LoD empty_lod;
+          if (var->IsType<framework::LoDTensor>()) {
+            // Clear all lod information for all lod_tensors.
+            auto *t = var->GetMutable<framework::LoDTensor>();
+            t->set_lod(empty_lod);
+          } else if (var->IsType<framework::LoDRankTable>()) {
+            auto *t = var->GetMutable<framework::LoDRankTable>();
+            t->Reset(empty_lod, 0);
+          }
         }
+        executor.RunPreparedContext(ctx.get(), &current_scope, false, false,
+                                    false);
+      }
+      scope.DeleteScope(&current_scope);
     }
   }
 };