[Async] Fix ClearListStmt metadata (taichi-dev#1873)

misc/visualize_state_flow_graph.py

@@ -32,10 +32,7 @@ def bar():
 
 
 def test_fusion():
-    ti.init(arch=ti.cpu,
-            async_mode=True,
-            async_opt_listgen=False,
-            async_opt_intermediate_file="fusion")
+    ti.init(arch=ti.cpu, async_mode=True, async_opt_intermediate_file="fusion")
 
     x = ti.field(ti.i32)
     y = ti.field(ti.i32)

taichi/program/async_engine.cpp

@@ -331,6 +331,9 @@ TaskMeta *get_task_meta(IRBank *ir_bank, const TaskLaunchRecord &t) {
         }
       }
     }
+    if (auto clear_list = stmt->cast<ClearListStmt>()) {
+      meta.output_states.emplace(clear_list->snode, AsyncState::Type::list);
+    }
     return false;
   });
   if (root_stmt->task_type == OffloadedStmt::listgen) {
@@ -345,16 +348,6 @@ TaskMeta *get_task_meta(IRBank *ir_bank, const TaskLaunchRecord &t) {
     meta.input_states.emplace(root_stmt->snode, AsyncState::Type::list);
   }
 
-  if (is_clear_list_task(root_stmt)) {
-    // ClearList completely erases the element list, so its output list state
-    // does NOT lead to a input state flow on the previous version of the list
-    // state. However, a dependency edge (instead of flow edge) will still be
-    // inserted since this is probably a WAR dependency.
-    // TODO: or might be WAW? Do we even need to distinguish WAW and WAR?
-
-    meta.output_states.emplace(get_snode_in_clear_list_task(root_stmt),
-                               AsyncState::Type::list);
-  }
   meta_bank[t.ir_handle] = meta;
   return &meta_bank[t.ir_handle];
 }