[Interpreter] Add a simple dead-code elimination bytecode optimizer.

test/unittests/interpreter/bytecode-dead-code-optimizer-unittest.cc

+// 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.
+
+#include "src/v8.h"
+
+#include "src/interpreter/bytecode-dead-code-optimizer.h"
+#include "src/interpreter/bytecode-label.h"
+#include "src/objects.h"
+#include "test/unittests/test-utils.h"
+
+namespace v8 {
+namespace internal {
+namespace interpreter {
+
+class BytecodeDeadCodeOptimizerTest : public BytecodePipelineStage,
+                                      public TestWithIsolateAndZone {
+ public:
+  BytecodeDeadCodeOptimizerTest() : dead_code_optimizer_(this) {}
+  ~BytecodeDeadCodeOptimizerTest() override {}
+
+  void Write(BytecodeNode* node) override {
+    write_count_++;
+    last_written_.Clone(node);
+  }
+
+  void WriteJump(BytecodeNode* node, BytecodeLabel* label) override {
+    write_count_++;
+    last_written_.Clone(node);
+  }
+
+  void BindLabel(BytecodeLabel* label) override {}
+  void BindLabel(const BytecodeLabel& target, BytecodeLabel* label) override {}
+  Handle<BytecodeArray> ToBytecodeArray(
+      int fixed_register_count, int parameter_count,
+      Handle<FixedArray> handle_table) override {
+    return Handle<BytecodeArray>();
+  }
+
+  BytecodeDeadCodeOptimizer* optimizer() { return &dead_code_optimizer_; }
+
+  int write_count() const { return write_count_; }
+  const BytecodeNode& last_written() const { return last_written_; }
+
+ private:
+  BytecodeDeadCodeOptimizer dead_code_optimizer_;
+
+  int write_count_ = 0;
+  BytecodeNode last_written_;
+};
+
+TEST_F(BytecodeDeadCodeOptimizerTest, LiveCodeKept) {
+  BytecodeNode add(Bytecode::kAdd, Register(0).ToOperand());
+  optimizer()->Write(&add);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(add, last_written());
+
+  BytecodeLabel target;
+  BytecodeNode jump(Bytecode::kJump, 0);
+  optimizer()->WriteJump(&jump, &target);
+  CHECK_EQ(write_count(), 2);
+  CHECK_EQ(jump, last_written());
+}
+
+TEST_F(BytecodeDeadCodeOptimizerTest, DeadCodeAfterReturnEliminated) {
+  BytecodeNode ret(Bytecode::kReturn);
+  optimizer()->Write(&ret);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(ret, last_written());
+
+  BytecodeNode add(Bytecode::kAdd, Register(0).ToOperand());
+  optimizer()->Write(&add);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(ret, last_written());
+}
+
+TEST_F(BytecodeDeadCodeOptimizerTest, DeadCodeAfterThrowEliminated) {
+  BytecodeNode thrw(Bytecode::kThrow);
+  optimizer()->Write(&thrw);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(thrw, last_written());
+
+  BytecodeNode add(Bytecode::kAdd, Register(0).ToOperand());
+  optimizer()->Write(&add);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(thrw, last_written());
+}
+
+TEST_F(BytecodeDeadCodeOptimizerTest, DeadCodeAfterReThrowEliminated) {
+  BytecodeNode rethrow(Bytecode::kReThrow);
+  optimizer()->Write(&rethrow);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(rethrow, last_written());
+
+  BytecodeNode add(Bytecode::kAdd, Register(0).ToOperand());
+  optimizer()->Write(&add);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(rethrow, last_written());
+}
+
+TEST_F(BytecodeDeadCodeOptimizerTest, DeadCodeAfterJumpEliminated) {
+  BytecodeLabel target;
+  BytecodeNode jump(Bytecode::kJump, 0);
+  optimizer()->WriteJump(&jump, &target);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(jump, last_written());
+
+  BytecodeNode add(Bytecode::kAdd, Register(0).ToOperand());
+  optimizer()->Write(&add);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(jump, last_written());
+}
+
+TEST_F(BytecodeDeadCodeOptimizerTest, DeadCodeStillDeadAfterConditinalJump) {
+  BytecodeNode ret(Bytecode::kReturn);
+  optimizer()->Write(&ret);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(ret, last_written());
+
+  BytecodeLabel target;
+  BytecodeNode jump(Bytecode::kJumpIfTrue, 0);
+  optimizer()->WriteJump(&jump, &target);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(ret, last_written());
+
+  BytecodeNode add(Bytecode::kAdd, Register(0).ToOperand());
+  optimizer()->Write(&add);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(ret, last_written());
+}
+
+TEST_F(BytecodeDeadCodeOptimizerTest, CodeLiveAfterLabelBind) {
+  BytecodeNode ret(Bytecode::kReturn);
+  optimizer()->Write(&ret);
+  CHECK_EQ(write_count(), 1);
+  CHECK_EQ(ret, last_written());
+
+  BytecodeLabel target;
+  optimizer()->BindLabel(&target);
+
+  BytecodeNode add(Bytecode::kAdd, Register(0).ToOperand());
+  optimizer()->Write(&add);
+  CHECK_EQ(write_count(), 2);
+  CHECK_EQ(add, last_written());
+}
+
+}  // namespace interpreter
+}  // namespace internal
+}  // namespace v8