Make FastNewFunctionContextStub take slots parameter

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 ac64f460f29ad4b7f492a71554ce6333b0fb321c..bf939a9295f457e07261f56ed659f6b55f0016e2 100644
--- a/src/compiler/js-generic-lowering.cc
+++ b/src/compiler/js-generic-lowering.cc
@@ -428,7 +428,8 @@ void JSGenericLowering::LowerJSCreateFunctionContext(Node* node) {
   // Use the FastNewFunctionContextStub only for function contexts up maximum
   // size.
   if (slot_count <= FastNewFunctionContextStub::kMaximumSlots) {

[klaasb, 2016/07/29 09:51:36]

What about this and similar lines elsewhere? I would remove them and the
alternate branches (calls to the runtime). See discussion in earlier patches.

-    Callable callable = CodeFactory::FastNewContext(isolate(), slot_count);
+    Callable callable = CodeFactory::FastNewContext(isolate());
+    node->InsertInput(zone(), 1, jsgraph()->Int32Constant(slot_count));

[Benedikt Meurer, 2016/07/29 03:29:16]

I'm not sure this is correct according to the interface descriptor (same for the
FCG versions). The interface descriptor declares the slots parameter as tagged,
but you are passing it as untagged signed32 value (and also use it that way in
the stub). I think for this to work you have to change the interface descriptor
to declare the parameter as signed32.

[klaasb, 2016/07/29 09:51:36]

Done.

     ReplaceWithStubCall(node, callable, flags);
   } else {
     ReplaceWithRuntimeCall(node, Runtime::kNewFunctionContext);