Ben Murdoch | 61f157c | 2016-09-16 13:49:30 +0100 | [diff] [blame] | 1 | // Copyright 2015 the V8 project authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | #ifndef V8_INTERPRETER_BYTECODE_LABEL_H_ |
| 6 | #define V8_INTERPRETER_BYTECODE_LABEL_H_ |
| 7 | |
| 8 | namespace v8 { |
| 9 | namespace internal { |
| 10 | namespace interpreter { |
| 11 | |
| 12 | // A label representing a branch target in a bytecode array. When a |
| 13 | // label is bound, it represents a known position in the bytecode |
| 14 | // array. For labels that are forward references there can be at most |
| 15 | // one reference whilst it is unbound. |
| 16 | class BytecodeLabel final { |
| 17 | public: |
| 18 | BytecodeLabel() : bound_(false), offset_(kInvalidOffset) {} |
| 19 | |
| 20 | bool is_bound() const { return bound_; } |
| 21 | size_t offset() const { return offset_; } |
| 22 | |
| 23 | private: |
| 24 | static const size_t kInvalidOffset = static_cast<size_t>(-1); |
| 25 | |
| 26 | void bind_to(size_t offset) { |
| 27 | DCHECK(!bound_ && offset != kInvalidOffset); |
| 28 | offset_ = offset; |
| 29 | bound_ = true; |
| 30 | } |
| 31 | |
| 32 | void set_referrer(size_t offset) { |
| 33 | DCHECK(!bound_ && offset != kInvalidOffset && offset_ == kInvalidOffset); |
| 34 | offset_ = offset; |
| 35 | } |
| 36 | |
| 37 | bool is_forward_target() const { |
| 38 | return offset() != kInvalidOffset && !is_bound(); |
| 39 | } |
| 40 | |
| 41 | // There are three states for a label: |
| 42 | // bound_ offset_ |
| 43 | // UNSET false kInvalidOffset |
| 44 | // FORWARD_TARGET false Offset of referring jump |
| 45 | // BACKWARD_TARGET true Offset of label in bytecode array when bound |
| 46 | bool bound_; |
| 47 | size_t offset_; |
| 48 | |
| 49 | friend class BytecodeArrayWriter; |
| 50 | }; |
| 51 | |
| 52 | } // namespace interpreter |
| 53 | } // namespace internal |
| 54 | } // namespace v8 |
| 55 | |
| 56 | #endif // V8_INTERPRETER_BYTECODE_LABEL_H_ |