Move desugaring of super calls with trailing spread to one runtime call.

src/interpreter/bytecode-generator.cc

Index: src/interpreter/bytecode-generator.cc
diff --git a/src/interpreter/bytecode-generator.cc b/src/interpreter/bytecode-generator.cc
index 1200cacd0707baeb4b9dbaf7ffbb079fc94479ad..45acc9991273a5c3234ff8f60e33281009257188 100644
--- a/src/interpreter/bytecode-generator.cc
+++ b/src/interpreter/bytecode-generator.cc
@@ -2486,24 +2486,68 @@ void BytecodeGenerator::VisitCallSuper(Call* expr) {
   Register constructor = this_function;  // Re-use dead this_function register.
   builder()->StoreAccumulatorInRegister(constructor);
 
-  RegisterList args =
-      register_allocator()->NewRegisterList(expr->arguments()->length());
-  VisitArguments(expr->arguments(), args);
+  ZoneList<Expression*>* args = expr->arguments();
+  RegisterList args_regs =
+      register_allocator()->NewRegisterList(args->length());
+
+  bool has_spread = false;
+  for (int i = 0; i < args->length(); i++) {
+    if (args->at(i)->IsSpread()) has_spread = true;
+  }
+
+  if (has_spread) {
+    // Pre-allocate regs for ReflectConstruct so we can use them.
+    RegisterList reflect_construct_args =
+        register_allocator()->NewRegisterList(4);
+
+    // Deal with the spread arg
+    if (args->length() == 1) {
+      Register spread_array = VisitForRegisterValue(
+          args->at(args->length() - 1)->AsSpread()->expression());
+      Runtime::FunctionId function_id = Runtime::kSpreadIterablePrepare;
+      builder()->CallRuntime(function_id, spread_array);
+    } else {
+      RegisterList spread_prepare_args =
+          register_allocator()->NewRegisterList(args->length());
+      // visit args at 0 --> length -2 inclusive
+      for (int i = 0; i < args->length() - 1; i++) {
+        VisitForRegisterValue(args->at(i), spread_prepare_args[i]);
+      }
+      // visit the spread
+      VisitForRegisterValue(
+          args->at(args->length() - 1)->AsSpread()->expression(),
+          spread_prepare_args[args->length() - 1]);
 
-  // The new target is loaded into the accumulator from the
-  // {new.target} variable.
-  VisitForAccumulatorValue(super->new_target_var());
+      Runtime::FunctionId function_id = Runtime::kSpreadIterablePrepareVarArgs;
+      builder()->CallRuntime(function_id, spread_prepare_args);
+    }
 
-  // Call construct.
-  builder()->SetExpressionPosition(expr);
-  // TODO(turbofan): For now we do gather feedback on super constructor
-  // calls, utilizing the existing machinery to inline the actual call
-  // target and the JSCreate for the implicit receiver allocation. This
-  // is not an ideal solution for super constructor calls, but it gets
-  // the job done for now. In the long run we might want to revisit this
-  // and come up with a better way.
-  int const feedback_slot_index = feedback_index(expr->CallFeedbackICSlot());
-  builder()->New(constructor, args, feedback_slot_index);
+    builder()->StoreAccumulatorInRegister(reflect_construct_args[2]);
+
+    // Do ReflectConstruct
+    Register receiver = reflect_construct_args[0];
+    builder()->LoadUndefined().StoreAccumulatorInRegister(receiver);
+    builder()->MoveRegister(constructor, reflect_construct_args[1]);
+    VisitForRegisterValue(super->new_target_var(), reflect_construct_args[3]);
+    builder()->CallJSRuntime(Context::REFLECT_CONSTRUCT_INDEX,
+                             reflect_construct_args);
+  } else {
+    VisitArguments(args, args_regs);
+    // The new target is loaded into the accumulator from the
+    // {new.target} variable.
+    VisitForAccumulatorValue(super->new_target_var());
+
+    // Call construct.
+    builder()->SetExpressionPosition(expr);
+    // TODO(turbofan): For now we do gather feedback on super constructor
+    // calls, utilizing the existing machinery to inline the actual call
+    // target and the JSCreate for the implicit receiver allocation. This
+    // is not an ideal solution for super constructor calls, but it gets
+    // the job done for now. In the long run we might want to revisit this
+    // and come up with a better way.
+    int const feedback_slot_index = feedback_index(expr->CallFeedbackICSlot());
+    builder()->New(constructor, args_regs, feedback_slot_index);
+  }
 }
 
 void BytecodeGenerator::VisitCallNew(CallNew* expr) {