[Interpreter] Ensure StackCheck bytecode handler is in split-edge form.

src/compiler/interpreter-assembler.cc

 // Copyright 2015 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/interpreter-assembler.h"
 
 #include <ostream>
 
 #include "src/code-factory.h"
 #include "src/compiler/graph.h"
@@ skipping 699 matching lines @@
   RawMachineLabel ok, stack_guard;
   Node* sp = raw_assembler_->LoadStackPointer();
   Node* stack_limit = raw_assembler_->Load(
       MachineType::Pointer(),
       raw_assembler_->ExternalConstant(
           ExternalReference::address_of_stack_limit(isolate())));
   Node* condition = raw_assembler_->UintPtrGreaterThanOrEqual(sp, stack_limit);
   raw_assembler_->Branch(condition, &ok, &stack_guard);
   raw_assembler_->Bind(&stack_guard);
   CallRuntime(Runtime::kStackGuard);
-  raw_assembler_->Goto(&ok);
-  raw_assembler_->Bind(&ok);
+  raw_assembler_->Fallthrough(&ok);

[Michael Starzinger, 2016/02/05 14:15:33]

Please don't add the "Fallthrough" helper to the RMA, this is very confusing.
The raw machine assembler is not in charge of maintaining edge-split form.
Similarly it is always possible to produce irreducible graphs with the RMA. IMHO
the layer above needs to maintain those invariants. Let's just model this here
as follows.

  raw_assembler_->Branch(condition, &overflow_no, &overflow_yes);
  raw_assembler_->Bind(&overflow_yes);
  CallRuntime(Runtime::kStackGuard);
  raw_assembler_->Goto(&end);
  raw_assembler_->Bind(&overflow_no);
  raw_assembler_->Goto(&end);
  raw_assembler_->Bind(&end);

The jump-threading will take care of optimizing these jumps.

[rmcilroy, 2016/02/05 14:34:36]

Done.

 }
 
 void InterpreterAssembler::Abort(BailoutReason bailout_reason) {
   Node* abort_id = SmiTag(Int32Constant(bailout_reason));
   Node* ret_value = CallRuntime(Runtime::kAbort, abort_id);
   // Unreached, but keeps turbofan happy.
   raw_assembler_->Return(ret_value);
 }
 
 
@@ skipping 37 matching lines @@
   return raw_assembler_->call_descriptor();
 }
 
 
 Zone* InterpreterAssembler::zone() { return raw_assembler_->zone(); }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8