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 8e251bbee1a45bc62689bff6f61a552e9b305773..0e1d4710036bf4a9ad45fe375ab4b982b5253351 100644
--- a/runtime/vm/kernel_to_il.cc
+++ b/runtime/vm/kernel_to_il.cc
@@ -720,6 +720,15 @@ 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

[Kevin Millikin (Google), 2017/02/22 10:42:17]

The comment is confusing.  It's not entirely clear what "the dart side" is.  I
guess that means, the Dart->Kernel translator, but I wouldn't assume here that
it's implemented in Dart and I'd just be explicit.

[jensj, 2017/02/23 09:40:26]

I have attempted to move the call to _asyncStackTraceHelper into the C++ code
instead (thus hidden behind the FLAG_causal_async_stacks).
I've thus removed the comment.

+      // 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);
+      }
+    }
   }
 }
 
@@ -2555,6 +2564,17 @@ Fragment FlowGraphBuilder::Return(TokenPosition position) {
         new (Z) DebugStepCheckInstr(position, RawPcDescriptors::kRuntimeCall);
   }
 
+  if (FLAG_causal_async_stacks &&
+      function.name() == Symbols::AsyncOperation().raw()) {

[Kevin Millikin (Google), 2017/02/22 10:42:18]

We should set the function to be correctly IsAsyncClosure or IsAsyncGenClosure
and use that instead of the name.

[jensj, 2017/02/23 09:40:26]

Done.

+    // 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);
 
@@ -3171,7 +3191,7 @@ 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.
-    intptr_t current_context_depth = context_depth_;
+    const 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.
@@ -3237,6 +3257,37 @@ FlowGraph* FlowGraphBuilder::BuildGraphOfFunction(FunctionNode* function,
     context_depth_ = current_context_depth;
   }
 
+  if (FLAG_causal_async_stacks &&
+      dart_function.name() == Symbols::AsyncOperation().raw()) {

[Kevin Millikin (Google), 2017/02/22 10:42:17]

Also here, I'd rather not use the name if we don't have to.

[jensj, 2017/02/23 09:40:26]

Done.

+    // 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
@@ -6131,7 +6182,8 @@ Fragment FlowGraphBuilder::TranslateFunctionNode(FunctionNode* node,
       // NOTE: This is not TokenPosition in the general sense!
       function = Function::NewClosureFunction(
           *name, parsed_function_->function(), position);
-      function.set_is_debuggable(node->debuggable());
+      function.set_is_debuggable(node->original_async_marker() ==
+                                 FunctionNode::kSync);
       function.set_end_token_pos(node->end_position());
       LocalScope* scope = scopes_->function_scopes[i].scope;
       const ContextScope& context_scope =