Revert "Enable causal stacktrace in kernel"

runtime/vm/kernel_to_il.cc

Index: runtime/vm/kernel_to_il.cc
diff --git a/runtime/vm/kernel_to_il.cc b/runtime/vm/kernel_to_il.cc
index fd383f817ff5b0b1b0ca1492cdfb0b8e0bbc153d..984de1d4aeabf6f9dda81ac56c48f9fd6ca966c9 100644
--- a/runtime/vm/kernel_to_il.cc
+++ b/runtime/vm/kernel_to_il.cc
@@ -720,15 +720,6 @@ void ScopeBuilder::VisitFunctionNode(FunctionNode* node) {
         scope_->CaptureVariable(temp);
       }
     }
-    if (FLAG_causal_async_stacks) {
-      // TODO(28777): Either remove the variable here, or update the dart side
-      // so we don't always generate it if this flag is not set.
-      LocalVariable* temp =
-          scope_->LookupVariable(Symbols::AsyncStackTraceVar(), true);
-      if (temp != NULL) {
-        scope_->CaptureVariable(temp);
-      }
-    }
   }
 }
 
@@ -2564,17 +2555,6 @@ Fragment FlowGraphBuilder::Return(TokenPosition position) {
         new (Z) DebugStepCheckInstr(position, RawPcDescriptors::kRuntimeCall);
   }
 
-  if (FLAG_causal_async_stacks &&
-      function.name() == Symbols::AsyncOperation().raw()) {
-    // We are returning from an asynchronous closure. Before we do that, be
-    // sure to clear the thread's asynchronous stack trace.
-    const Function& target = Function::ZoneHandle(
-        Z, I->object_store()->async_clear_thread_stack_trace());
-    ASSERT(!target.IsNull());
-    instructions += StaticCall(TokenPosition::kNoSource, target, 0);
-    instructions += Drop();
-  }
-
   ReturnInstr* return_instr = new (Z) ReturnInstr(position, value);
   if (exit_collector_ != NULL) exit_collector_->AddExit(return_instr);
 
@@ -3191,7 +3171,7 @@ FlowGraph* FlowGraphBuilder::BuildGraphOfFunction(FunctionNode* function,
     // The code we are building will be executed right after we enter
     // the function and before any nested contexts are allocated.
     // Reset current context_depth_ to match this.
-    const intptr_t current_context_depth = context_depth_;
+    intptr_t current_context_depth = context_depth_;
     context_depth_ = scopes_->yield_jump_variable->owner()->context_level();
 
     // Prepend an entry corresponding to normal entry to the function.
@@ -3257,37 +3237,6 @@ FlowGraph* FlowGraphBuilder::BuildGraphOfFunction(FunctionNode* function,
     context_depth_ = current_context_depth;
   }
 
-  if (FLAG_causal_async_stacks &&
-      dart_function.name() == Symbols::AsyncOperation().raw()) {
-    // The code we are building will be executed right after we enter
-    // the function and before any nested contexts are allocated.
-    // Reset current context_depth_ to match this.
-    const intptr_t current_context_depth = context_depth_;
-    context_depth_ = scopes_->yield_jump_variable->owner()->context_level();
-
-    Fragment instructions;
-    LocalScope* scope = parsed_function_->node_sequence()->scope();
-
-    const Function& target = Function::ZoneHandle(
-        Z, I->object_store()->async_set_thread_stack_trace());
-    ASSERT(!target.IsNull());
-
-    // Fetch and load :async_stack_trace
-    LocalVariable* async_stack_trace_var =
-        scope->LookupVariable(Symbols::AsyncStackTraceVar(), false);
-    ASSERT((async_stack_trace_var != NULL) &&
-           async_stack_trace_var->is_captured());
-    instructions += LoadLocal(async_stack_trace_var);
-    instructions += PushArgument();
-
-    // Call _asyncSetThreadStackTrace
-    instructions += StaticCall(TokenPosition::kNoSource, target, 1);
-    instructions += Drop();
-
-    body = instructions + body;
-    context_depth_ = current_context_depth;
-  }
-
   if (FLAG_support_debugger && function->position().IsDebugPause() &&
       !dart_function.is_native() && dart_function.is_debuggable()) {
     // If a switch was added above: Start the switch by injecting a debugable