[es6] Perform the IsConstructor test in GetSuperConstructor.

src/compiler/js-generic-lowering.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/js-generic-lowering.h"
 
 #include "src/ast/ast.h"
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
 #include "src/compiler/common-operator.h"
@@ skipping 327 matching lines @@
 
 
 void JSGenericLowering::LowerJSDeleteProperty(Node* node) {
   LanguageMode language_mode = OpParameter<LanguageMode>(node);
   ReplaceWithRuntimeCall(node, is_strict(language_mode)
                                    ? Runtime::kDeleteProperty_Strict
                                    : Runtime::kDeleteProperty_Sloppy);
 }
 
 
+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());
   ReplaceWithStubCall(node, callable, flags);
 }
 
 
 void JSGenericLowering::LowerJSLoadContext(Node* node) {
   const ContextAccess& access = ContextAccessOf(node->op());
   for (size_t i = 0; i < access.depth(); ++i) {
@@ skipping 332 matching lines @@
 }
 
 
 MachineOperatorBuilder* JSGenericLowering::machine() const {
   return jsgraph()->machine();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8