[es6] Perform the IsConstructor test in GetSuperConstructor.

src/compiler/js-generic-lowering.cc

Index: src/compiler/js-generic-lowering.cc
diff --git a/src/compiler/js-generic-lowering.cc b/src/compiler/js-generic-lowering.cc
index ac36cc7913a82db3976569aa182831692be718f0..0100e80476fd731c0dc9472b52955c7ba7d03ada 100644
--- a/src/compiler/js-generic-lowering.cc
+++ b/src/compiler/js-generic-lowering.cc
@@ -345,6 +345,16 @@ void JSGenericLowering::LowerJSDeleteProperty(Node* node) {
 }
 
 
+void JSGenericLowering::LowerJSGetSuperConstructor(Node* node) {
+  // The typeof operator doesn't need the current context.
+  NodeProperties::ReplaceContextInput(node, jsgraph()->NoContextConstant());

[caitp, 2016/11/21 13:52:53]

I would just replace this whole block with `ReplaceWithRuntimeCall(node,
Runtime::kGetSuperConstructor);`,  for now (unless we already have a codestub
for this).

I'm not sure exactly how the pipeline works, but I feel in the monomorphic case
we should be able to eliminate the IsConstructor() check and the CallRuntime() /
Throw(), but I'm actually not positive how to do that with js operators.

@bmeurer?

[Benedikt Meurer, 2016/11/23 04:51:00]

This should use the GetSuperConstructor builtin:

CallDescriptor::Flags flags = FrameStateFlagFor(node);
Callable callable = CodeFactory::GetSuperConstructor(isolate());
ReplaceWithStubCall(node, callable, flags);

We will eventually turn the GetSuperConstructor bytecode into an IC and collect
feedback that will allow us to eliminate and constant-fold it completely most of
the time. But the generic case still matters.

+  Callable callable = CodeFactory::Typeof(isolate());
+  node->AppendInput(zone(), graph()->start());
+  ReplaceWithStubCall(node, callable, CallDescriptor::kNoAllocate,
+                      Operator::kEliminatable);
+}
+
+
 void JSGenericLowering::LowerJSInstanceOf(Node* node) {
   CallDescriptor::Flags flags = FrameStateFlagForCall(node);
   Callable callable = CodeFactory::InstanceOf(isolate());