[ignition] Refactor array iterator to separate out access

src/interpreter/bytecode-array-accessor.h

-// Copyright 2015 the V8 project authors. All rights reserved.
+// Copyright 2016 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.
 
-#ifndef V8_INTERPRETER_BYTECODE_ARRAY_ITERATOR_H_
-#define V8_INTERPRETER_BYTECODE_ARRAY_ITERATOR_H_
+#ifndef V8_INTERPRETER_BYTECODE_ARRAY_ACCESSOR_H_
+#define V8_INTERPRETER_BYTECODE_ARRAY_ACCESSOR_H_
 
 #include "src/globals.h"
 #include "src/handles.h"
 #include "src/interpreter/bytecode-register.h"
 #include "src/interpreter/bytecodes.h"
 #include "src/objects.h"
 #include "src/runtime/runtime.h"
 
 namespace v8 {
 namespace internal {
 namespace interpreter {
 
-class V8_EXPORT_PRIVATE BytecodeArrayIterator {
+class V8_EXPORT_PRIVATE BytecodeArrayAccessor {
  public:
-  explicit BytecodeArrayIterator(Handle<BytecodeArray> bytecode_array);
+  BytecodeArrayAccessor(Handle<BytecodeArray> bytecode_array,
+                        int initial_offset);
 
-  void Advance();
-  bool done() const;
+  void SetOffset(int offset);
+  bool OffsetInBounds() const;

[rmcilroy, 2016/11/21 14:14:26]

nit - make this private, and just OffsetIsValid() ? 

Maybe just DCHECK this on SetOffset and have the rest of the code assume it is
valid (no ifs) ?

[Leszek Swirski, 2016/11/21 16:49:03]

yes to private, I want to keep OffsetInBounds though because we're not doing
other validity checks (e.g. is a valid bytecode)

We can't do a DCHECK, because this would break the functionality of
BytecodeArrayIterator.Advance, which can advance the offset past the end of the
array, and relies on this to determine if it's done.

+
   Bytecode current_bytecode() const;
   int current_bytecode_size() const;
   int current_offset() const { return bytecode_offset_; }
   OperandScale current_operand_scale() const { return operand_scale_; }
   int current_prefix_offset() const { return prefix_offset_; }
   const Handle<BytecodeArray>& bytecode_array() const {
     return bytecode_array_;
   }
 
   uint32_t GetFlagOperand(int operand_index) const;
@@ skipping 17 matching lines @@
                               OperandType operand_type) const;
   int32_t GetSignedOperand(int operand_index, OperandType operand_type) const;
 
   void UpdateOperandScale();
 
   Handle<BytecodeArray> bytecode_array_;
   int bytecode_offset_;
   OperandScale operand_scale_;
   int prefix_offset_;
 
-  DISALLOW_COPY_AND_ASSIGN(BytecodeArrayIterator);
+  DISALLOW_COPY_AND_ASSIGN(BytecodeArrayAccessor);
 };
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_INTERPRETER_BYTECODE_GRAPH_ITERATOR_H_
+#endif  // V8_INTERPRETER_BYTECODE_GRAPH_ACCESSOR_H_