Revert "Proper sequencing of _asyncStackTraceHelper in Kernel"

runtime/vm/kernel_binary_flowgraph.cc

Index: runtime/vm/kernel_binary_flowgraph.cc
diff --git a/runtime/vm/kernel_binary_flowgraph.cc b/runtime/vm/kernel_binary_flowgraph.cc
index 6d0725dce7990bae6ea00ea0de7bee9da9899048..37f596c4fa2535ec5c15ee3e6198bac1a1ef6388 100644
--- a/runtime/vm/kernel_binary_flowgraph.cc
+++ b/runtime/vm/kernel_binary_flowgraph.cc
@@ -3287,6 +3287,32 @@ FlowGraph* StreamingFlowGraphBuilder::BuildGraphOfFunction(
 
   SkipDartType();  // read return type.
 
+  if (FLAG_causal_async_stacks &&
+      (dart_function.IsAsyncFunction() || dart_function.IsAsyncGenerator())) {
+    LocalScope* scope = parsed_function()->node_sequence()->scope();
+    // :async_stack_trace = _asyncStackTraceHelper(:async_op);
+    const dart::Library& async_lib =
+        dart::Library::Handle(dart::Library::AsyncLibrary());
+    const Function& target = Function::ZoneHandle(
+        Z,
+        async_lib.LookupFunctionAllowPrivate(Symbols::AsyncStackTraceHelper()));
+    ASSERT(!target.IsNull());
+
+    // TODO(johnmccutchan): Why does this have the null value?
+    LocalVariable* async_op =
+        scope->child()->LookupVariable(Symbols::AsyncOperation(), false);
+    ASSERT(async_op != NULL);
+    ASSERT(async_op->is_captured());
+    body += LoadLocal(async_op);
+    body += PushArgument();
+    body += StaticCall(TokenPosition::kNoSource, target, 1);
+    LocalVariable* async_stack_trace_var =
+        scope->LookupVariable(Symbols::AsyncStackTraceVar(), false);
+    ASSERT(async_stack_trace_var != NULL);
+    body += StoreLocal(TokenPosition::kNoSource, async_stack_trace_var);
+    body += Drop();
+  }
+
   bool has_body = ReadTag() == kSomething;  // read first part of body.
 
   if (dart_function.is_native()) {