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

Adds back simple dead code elimination to the bytecode pipeline.

BUG=v8:4280,chromium:616064

Review-Url: https://codereview.chromium.org/2038083002
Cr-Commit-Position: refs/heads/master@{#37147}

BUILD.gn

@@ -1222,6 +1222,8 @@ v8_source_set("v8_base") {
     "src/interpreter/bytecode-array-iterator.h",
     "src/interpreter/bytecode-array-writer.cc",
     "src/interpreter/bytecode-array-writer.h",
+    "src/interpreter/bytecode-dead-code-optimizer.cc",
+    "src/interpreter/bytecode-dead-code-optimizer.h",
     "src/interpreter/bytecode-generator.cc",
     "src/interpreter/bytecode-generator.h",
     "src/interpreter/bytecode-label.h",

src/flag-definitions.h

@@ -306,6 +306,8 @@ DEFINE_BOOL(ignition_eager, false, "eagerly compile and parse with ignition")
 DEFINE_BOOL(ignition_generators, true,
             "enable experimental ignition support for generators")
 DEFINE_STRING(ignition_filter, "*", "filter for ignition interpreter")
+DEFINE_BOOL(ignition_deadcode, true,
+            "use ignition dead code elimination optimizer")
 DEFINE_BOOL(ignition_peephole, true, "use ignition peephole optimizer")
 DEFINE_BOOL(ignition_reo, true, "use ignition register equivalence optimizer")
 DEFINE_BOOL(ignition_filter_expression_positions, true,

src/interpreter/bytecode-array-builder.cc

@@ -6,6 +6,7 @@
 
 #include "src/compiler.h"
 #include "src/interpreter/bytecode-array-writer.h"
+#include "src/interpreter/bytecode-dead-code-optimizer.h"
 #include "src/interpreter/bytecode-label.h"
 #include "src/interpreter/bytecode-peephole-optimizer.h"
 #include "src/interpreter/bytecode-register-optimizer.h"
@@ -35,6 +36,10 @@ BytecodeArrayBuilder::BytecodeArrayBuilder(Isolate* isolate, Zone* zone,
   DCHECK_GE(context_register_count_, 0);
   DCHECK_GE(local_register_count_, 0);
 
+  if (FLAG_ignition_deadcode) {
+    pipeline_ = new (zone) BytecodeDeadCodeOptimizer(pipeline_);
+  }
+
   if (FLAG_ignition_peephole) {
     pipeline_ = new (zone)
         BytecodePeepholeOptimizer(&constant_array_builder_, pipeline_);

src/interpreter/bytecode-dead-code-optimizer.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/interpreter/bytecode-dead-code-optimizer.h"
+
+namespace v8 {
+namespace internal {
+namespace interpreter {
+
+BytecodeDeadCodeOptimizer::BytecodeDeadCodeOptimizer(
+    BytecodePipelineStage* next_stage)
+    : next_stage_(next_stage), exit_seen_in_block_(false) {}
+
+// override
+Handle<BytecodeArray> BytecodeDeadCodeOptimizer::ToBytecodeArray(
+    int fixed_register_count, int parameter_count,
+    Handle<FixedArray> handler_table) {
+  return next_stage_->ToBytecodeArray(fixed_register_count, parameter_count,
+                                      handler_table);
+}
+
+// override
+void BytecodeDeadCodeOptimizer::Write(BytecodeNode* node) {
+  // Don't emit dead code.
+  if (exit_seen_in_block_) return;
+
+  switch (node->bytecode()) {
+    case Bytecode::kReturn:
+    case Bytecode::kThrow:
+    case Bytecode::kReThrow:
+      exit_seen_in_block_ = true;
+      break;
+    default:
+      break;
+  }
+
+  next_stage_->Write(node);
+}
+
+// override
+void BytecodeDeadCodeOptimizer::WriteJump(BytecodeNode* node,
+                                          BytecodeLabel* label) {
+  // Don't emit dead code.
+  // TODO(rmcilroy): For forward jumps we could mark the label as dead, thereby
+  // avoiding emitting dead code when we bind the label.
+  if (exit_seen_in_block_) return;
+
+  switch (node->bytecode()) {
+    case Bytecode::kJump:
+    case Bytecode::kJumpConstant:
+      exit_seen_in_block_ = true;
+      break;
+    default:
+      break;
+  }
+
+  next_stage_->WriteJump(node, label);
+}
+
+// override
+void BytecodeDeadCodeOptimizer::BindLabel(BytecodeLabel* label) {
+  next_stage_->BindLabel(label);
+  exit_seen_in_block_ = false;
+}
+
+// override
+void BytecodeDeadCodeOptimizer::BindLabel(const BytecodeLabel& target,
+                                          BytecodeLabel* label) {
+  next_stage_->BindLabel(target, label);
+  // exit_seen_in_block_ was reset when target was bound, so shouldn't be
+  // changed here.
+}
+
+}  // namespace interpreter
+}  // namespace internal
+}  // namespace v8

src/interpreter/bytecode-dead-code-optimizer.h

+// 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_DEAD_CODE_OPTIMIZER_H_
+#define V8_INTERPRETER_BYTECODE_DEAD_CODE_OPTIMIZER_H_
+
+#include "src/interpreter/bytecode-pipeline.h"
+
+namespace v8 {
+namespace internal {
+namespace interpreter {
+
+// An optimization stage for eliminating obviously dead code in bytecode
+// generation.
+class BytecodeDeadCodeOptimizer final : public BytecodePipelineStage,
+                                        public ZoneObject {
+ public:
+  explicit BytecodeDeadCodeOptimizer(BytecodePipelineStage* next_stage);
+
+  // BytecodePipelineStage interface.
+  void Write(BytecodeNode* node) override;
+  void WriteJump(BytecodeNode* node, BytecodeLabel* label) override;
+  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> handler_table) override;
+
+ private:
+  BytecodePipelineStage* next_stage_;
+  bool exit_seen_in_block_;
+
+  DISALLOW_COPY_AND_ASSIGN(BytecodeDeadCodeOptimizer);
+};
+
+}  // namespace interpreter
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_INTERPRETER_BYTECODE_DEAD_CODE_OPTIMIZER_H_

src/v8.gyp

@@ -898,7 +898,11 @@
         'interpreter/bytecode-array-iterator.h',
         'interpreter/bytecode-array-writer.cc',
         'interpreter/bytecode-array-writer.h',
+        'interpreter/bytecode-dead-code-optimizer.cc',
+        'interpreter/bytecode-dead-code-optimizer.h',
         'interpreter/bytecode-label.h',
+        'interpreter/bytecode-generator.cc',
+        'interpreter/bytecode-generator.h',
         'interpreter/bytecode-peephole-optimizer.cc',
         'interpreter/bytecode-peephole-optimizer.h',
         'interpreter/bytecode-pipeline.cc',
@@ -907,8 +911,6 @@
         'interpreter/bytecode-register-allocator.h',
         'interpreter/bytecode-register-optimizer.cc',
         'interpreter/bytecode-register-optimizer.h',
-        'interpreter/bytecode-generator.cc',
-        'interpreter/bytecode-generator.h',
         'interpreter/bytecode-traits.h',
         'interpreter/constant-array-builder.cc',
         'interpreter/constant-array-builder.h',

test/cctest/interpreter/bytecode_expectations/ContextVariables.golden

@@ -105,7 +105,7 @@ snippet: "
 "
 frame size: 4
 parameter count: 1
-bytecode array length: 48
+bytecode array length: 46
 bytecodes: [
                 B(CallRuntime), U16(Runtime::kNewFunctionContext), R(closure), U8(1),
                 B(PushContext), R(0),
@@ -126,7 +126,6 @@ bytecodes: [
   /*   72 S> */ B(CreateClosure), U8(1), U8(0),
                 B(PopContext), R(0),
   /*  104 S> */ B(Return),
-                B(PopContext), R(1),
 ]
 constant pool: [
   InstanceType::FIXED_ARRAY_TYPE,

test/cctest/interpreter/bytecode_expectations/DoExpression.golden

@@ -54,7 +54,7 @@ snippet: "
 "
 frame size: 2
 parameter count: 1
-bytecode array length: 24
+bytecode array length: 17
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   34 E> */ B(StackCheck),
@@ -63,11 +63,8 @@ bytecodes: [
   /*   69 S> */ B(Inc),
                 B(Star), R(1),
                 B(Star), R(0),
-  /*   74 S> */ B(Jump), U8(11),
-                B(Mov), R(0), R(1),
-  /*   84 S> */ B(LdaSmi), U8(20),
-                B(Star), R(1),
-                B(Jump), U8(-19),
+  /*   74 S> */ B(Jump), U8(4),
+                B(Jump), U8(-12),
                 B(LdaUndefined),
   /*   94 S> */ B(Return),
 ]

test/cctest/interpreter/bytecode_expectations/IfConditions.golden

@@ -150,15 +150,14 @@ snippet: "
 "
 frame size: 0
 parameter count: 2
-bytecode array length: 20
+bytecode array length: 18
 bytecodes: [
   /*   10 E> */ B(StackCheck),
   /*   18 S> */ B(LdaZero),
   /*   24 E> */ B(TestLessThanOrEqual), R(arg0),
-                B(JumpIfFalse), U8(9),
+                B(JumpIfFalse), U8(7),
   /*   36 S> */ B(Wide), B(LdaSmi), U16(200),
   /*   80 S> */ B(Return),
-                B(Jump), U8(7),
   /*   63 S> */ B(Wide), B(LdaSmi), U16(-200),
   /*   80 S> */ B(Return),
                 B(LdaUndefined),
@@ -262,7 +261,7 @@ snippet: "
 "
 frame size: 2
 parameter count: 2
-bytecode array length: 411
+bytecode array length: 409
 bytecodes: [
   /*   10 E> */ B(StackCheck),
   /*   24 S> */ B(LdaZero),
@@ -402,7 +401,6 @@ bytecodes: [
   /* 1073 S> */ B(Mov), R(1), R(0),
   /* 1081 S> */ B(Wide), B(LdaSmi), U16(200),
   /* 1117 S> */ B(Return),
-                B(Jump), U8(7),
   /* 1102 S> */ B(Wide), B(LdaSmi), U16(-200),
   /* 1117 S> */ B(Return),
                 B(LdaUndefined),
@@ -490,7 +488,7 @@ snippet: "
 "
 frame size: 2
 parameter count: 1
-bytecode array length: 409
+bytecode array length: 407
 bytecodes: [
   /*   10 E> */ B(StackCheck),
   /*   25 S> */ B(LdaZero),
@@ -629,7 +627,6 @@ bytecodes: [
   /* 1067 S> */ B(Mov), R(1), R(0),
   /* 1076 S> */ B(Wide), B(LdaSmi), U16(200),
   /* 1112 S> */ B(Return),
-                B(Jump), U8(7),
   /* 1097 S> */ B(Wide), B(LdaSmi), U16(-200),
   /* 1112 S> */ B(Return),
                 B(LdaUndefined),
@@ -723,15 +720,14 @@ snippet: "
 "
 frame size: 1
 parameter count: 1
-bytecode array length: 16
+bytecode array length: 14
 bytecodes: [
   /*   10 E> */ B(StackCheck),
   /*   25 S> */ B(LdaZero),
                 B(Star), R(0),
-  /*   30 S> */ B(JumpIfToBooleanFalse), U8(7),
+  /*   30 S> */ B(JumpIfToBooleanFalse), U8(5),
   /*   43 S> */ B(LdaSmi), U8(20),
   /*   85 S> */ B(Return),
-                B(Jump), U8(5),
   /*   69 S> */ B(LdaSmi), U8(-20),
   /*   85 S> */ B(Return),
                 B(LdaUndefined),

test/cctest/interpreter/bytecode_expectations/Throw.golden

@@ -13,13 +13,11 @@ snippet: "
 "
 frame size: 0
 parameter count: 1
-bytecode array length: 6
+bytecode array length: 4
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   34 S> */ B(LdaSmi), U8(1),
   /*   34 E> */ B(Throw),
-                B(LdaUndefined),
-  /*   43 S> */ B(Return),
 ]
 constant pool: [
 ]
@@ -32,13 +30,11 @@ snippet: "
 "
 frame size: 0
 parameter count: 1
-bytecode array length: 6
+bytecode array length: 4
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   34 S> */ B(LdaConstant), U8(0),
   /*   34 E> */ B(Throw),
-                B(LdaUndefined),
-  /*   49 S> */ B(Return),
 ]
 constant pool: [
   "Error",

test/cctest/interpreter/bytecode_expectations/TryCatch.golden

@@ -13,13 +13,13 @@ snippet: "
 "
 frame size: 5
 parameter count: 1
-bytecode array length: 43
+bytecode array length: 41
 bytecodes: [
   /*   30 E> */ B(StackCheck),
                 B(Mov), R(context), R(1),
   /*   40 S> */ B(LdaSmi), U8(1),
   /*   75 S> */ B(Return),
-                B(Jump), U8(34),
+                B(Jump), U8(32),
                 B(Star), R(3),
                 B(LdaConstant), U8(0),
                 B(Star), R(2),
@@ -32,7 +32,6 @@ bytecodes: [
   /*   63 S> */ B(LdaSmi), U8(2),
                 B(PopContext), R(0),
   /*   75 S> */ B(Return),
-                B(PopContext), R(0),
                 B(LdaUndefined),
   /*   75 S> */ B(Return),
 ]

test/cctest/interpreter/bytecode_expectations/WithStatement.golden

@@ -13,7 +13,7 @@ snippet: "
 "
 frame size: 4
 parameter count: 1
-bytecode array length: 27
+bytecode array length: 25
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   34 S> */ B(CreateObjectLiteral), U8(0), U8(0), U8(1),
@@ -26,7 +26,6 @@ bytecodes: [
   /*   50 S> */ B(LdaLookupSlot), U8(1),
                 B(PopContext), R(0),
   /*   62 S> */ B(Return),
-                B(PopContext), R(0),
 ]
 constant pool: [
   InstanceType::FIXED_ARRAY_TYPE,

test/cctest/interpreter/test-interpreter.cc

@@ -1053,7 +1053,7 @@ TEST(InterpreterJumpConstantWith16BitOperand) {
                                0, 257);
 
   Register reg(0), scratch(256);
-  BytecodeLabel done;
+  BytecodeLabel done, fake;
 
   builder.LoadLiteral(Smi::FromInt(0));
   builder.StoreAccumulatorInRegister(reg);
@@ -1066,6 +1066,7 @@ TEST(InterpreterJumpConstantWith16BitOperand) {
   builder.Jump(&done);
 
   // Emit more than 16-bit immediate operands worth of code to jump over.
+  builder.Bind(&fake);
   for (int i = 0; i < 6600; i++) {
     builder.LoadLiteral(Smi::FromInt(0));                 // 1-byte
     builder.BinaryOperation(Token::Value::ADD, scratch);  // 4-bytes

test/cctest/interpreter/test-source-positions.cc

@@ -22,8 +22,9 @@ namespace interpreter {
 #define OPTIMIZATION_FLAGS(V)                                                 \
   V(FLAG_ignition_reo, kUseReo, 0)                                            \
   V(FLAG_ignition_peephole, kUsePeephole, 1)                                  \
-  V(FLAG_ignition_filter_expression_positions, \
-    kUseUseFilterExpressionPositions, 2)
+  V(FLAG_ignition_filter_expression_positions, kUseFilterExpressionPositions, \
+    2)                                                                        \
+  V(FLAG_ignition_deadcode, kUseDeadCode, 3)
 
 #define DECLARE_BIT(_, Name, BitIndex) static const int Name = 1 << BitIndex;
 OPTIMIZATION_FLAGS(DECLARE_BIT)
@@ -35,14 +36,19 @@ OPTIMIZATION_FLAGS(DECLARE_BIT)
 #define TEST_CASES(V)                                              \
   V(UsingReo, kUseReo)                                             \
   V(UsingPeephole, kUsePeephole)                                   \
+  V(UsingDeadCode, kUseDeadCode)                                   \
+  V(UsingFilterExpressionPositions, kUseFilterExpressionPositions) \
   V(UsingReoAndPeephole, kUseReo | kUsePeephole)                   \
-  V(UsingUseFilterExpressionPositions, kUseUseFilterExpressionPositions) \
-  V(UsingReoAndUseFilterExpressionPositions,                             \
-    kUseReo | kUseUseFilterExpressionPositions)                          \
-  V(UsingPeepholeAndUseFilterExpressionPositions,                        \
-    kUsePeephole | kUseUseFilterExpressionPositions)                     \
+  V(UsingReoAndFilterExpressionPositions,                          \
+    kUseReo | kUseFilterExpressionPositions)                       \
+  V(UsingReoAndDeadCode, kUseReo | kUseDeadCode)                   \
+  V(UsingPeepholeAndFilterExpressionPositions,                     \
+    kUsePeephole | kUseFilterExpressionPositions)                  \
+  V(UsingPeepholeAndDeadCode, kUsePeephole | kUseDeadCode)         \
+  V(UsingFilterExpressionPositionsAndDeadCode,                     \
+    kUseFilterExpressionPositions | kUseDeadCode)                  \
   V(UsingAllOptimizations,                                         \
-    kUseReo | kUsePeephole | kUseUseFilterExpressionPositions)
+    kUseReo | kUsePeephole | kUseFilterExpressionPositions | kUseDeadCode)
 
 struct TestCaseData {
   TestCaseData(const char* const script,
@@ -142,9 +148,7 @@ class OptimizedBytecodeSourcePositionTester final {
                                      const char* function_body,
                                      const char* function_decl_params,
                                      const char* function_args);
-  static std::string MakeFunctionName(int optimization_bitmap);
-  static std::string MakeScript(const char* function_name,
-                                const char* function_body,
+  static std::string MakeScript(const char* function_body,
                                 const char* function_decl_params,
                                 const char* function_args);
 
@@ -160,39 +164,30 @@ class OptimizedBytecodeSourcePositionTester final {
   bool saved_flag_always_opt_;
 };
 
-// static
-std::string OptimizedBytecodeSourcePositionTester::MakeFunctionName(
-    int optimization_bitmap) {
-  std::ostringstream os;
-  os << "test_function_" << optimization_bitmap;
-  return os.str();
-}
-
 // static
 std::string OptimizedBytecodeSourcePositionTester::MakeScript(
-    const char* function_name, const char* function_body,
-    const char* function_decl_params, const char* function_args) {
+    const char* function_body, const char* function_decl_params,
+    const char* function_args) {
   std::ostringstream os;
-  os << "function " << function_name << "(" << function_decl_params << ") {";
+  os << "function test_function"
+     << "(" << function_decl_params << ") {";
   os << function_body;
   os << "}";
-  os << function_name << "(" << function_args << ");";
+  os << "test_function(" << function_args << ");";
   return os.str();
 }
 
 Handle<BytecodeArray> OptimizedBytecodeSourcePositionTester::MakeBytecode(
     int optimization_bitmap, const char* function_body,
     const char* function_decl_params, const char* function_args) {
-  std::string function_name = MakeFunctionName(optimization_bitmap);
-  std::string script = MakeScript(function_name.c_str(), function_body,
-                                  function_decl_params, function_args);
+  std::string script =
+      MakeScript(function_body, function_decl_params, function_args);
   SetOptimizationFlags(optimization_bitmap);
   CompileRun(script.c_str());
 
-  Local<Function> api_function =
-      Local<Function>::Cast(CcTest::global()
-                                ->Get(CcTest::isolate()->GetCurrentContext(),
-                                      v8_str(function_name.c_str()))
+  Local<Function> api_function = Local<Function>::Cast(
+      CcTest::global()
+          ->Get(CcTest::isolate()->GetCurrentContext(), v8_str("test_function"))
           .ToLocalChecked());
   Handle<JSFunction> function =
       Handle<JSFunction>::cast(v8::Utils::OpenHandle(*api_function));

test/unittests/BUILD.gn

@@ -90,6 +90,7 @@ v8_executable("unittests") {
     "interpreter/bytecode-array-builder-unittest.cc",
     "interpreter/bytecode-array-iterator-unittest.cc",
     "interpreter/bytecode-array-writer-unittest.cc",
+    "interpreter/bytecode-dead-code-optimizer-unittest.cc",
     "interpreter/bytecode-peephole-optimizer-unittest.cc",
     "interpreter/bytecode-pipeline-unittest.cc",
     "interpreter/bytecode-register-allocator-unittest.cc",

test/unittests/interpreter/bytecode-array-builder-unittest.cc

@@ -171,15 +171,22 @@ TEST_F(BytecodeArrayBuilderTest, AllBytecodesGenerated) {
   // Emit control flow. Return must be the last instruction.
   BytecodeLabel start;
   builder.Bind(&start);
+  {
     // Short jumps with Imm8 operands
+    BytecodeLabel after_jump;
     builder.Jump(&start)
+        .Bind(&after_jump)
         .JumpIfNull(&start)
         .JumpIfUndefined(&start)
         .JumpIfNotHole(&start);
+  }
 
   // Longer jumps with constant operands
   BytecodeLabel end[8];
+  {
+    BytecodeLabel after_jump;
     builder.Jump(&end[0])
+        .Bind(&after_jump)
         .LoadTrue()
         .JumpIfTrue(&end[1])
         .LoadTrue()
@@ -191,6 +198,7 @@ TEST_F(BytecodeArrayBuilderTest, AllBytecodesGenerated) {
         .JumpIfNull(&end[5])
         .JumpIfUndefined(&end[6])
         .JumpIfNotHole(&end[7]);
+  }
 
   // Perform an operation that returns boolean value to
   // generate JumpIfTrue/False
@@ -209,8 +217,13 @@ TEST_F(BytecodeArrayBuilderTest, AllBytecodesGenerated) {
     builder.LoadTrue();
   }
   // Longer jumps requiring Constant operand
-  builder.Jump(&start).JumpIfNull(&start).JumpIfUndefined(&start).JumpIfNotHole(
-      &start);
+  {
+    BytecodeLabel after_jump;
+    builder.Jump(&start)
+        .Bind(&after_jump)
+        .JumpIfNull(&start)
+        .JumpIfUndefined(&start)
+        .JumpIfNotHole(&start);
     // Perform an operation that returns boolean value to
     // generate JumpIfTrue/False
     builder.CompareOperation(Token::Value::EQ, reg)
@@ -223,6 +236,7 @@ TEST_F(BytecodeArrayBuilderTest, AllBytecodesGenerated) {
         .JumpIfTrue(&start)
         .BinaryOperation(Token::Value::ADD, reg)
         .JumpIfFalse(&start);
+  }
 
   // Emit stack check bytecode.
   builder.StackCheck(0);
@@ -230,9 +244,9 @@ TEST_F(BytecodeArrayBuilderTest, AllBytecodesGenerated) {
   // Emit throw and re-throw in it's own basic block so that the rest of the
   // code isn't omitted due to being dead.
   BytecodeLabel after_throw;
-  builder.Jump(&after_throw).Throw().Bind(&after_throw);
+  builder.Throw().Bind(&after_throw);
   BytecodeLabel after_rethrow;
-  builder.Jump(&after_rethrow).ReThrow().Bind(&after_rethrow);
+  builder.ReThrow().Bind(&after_rethrow);
 
   builder.ForInPrepare(reg)
       .ForInDone(reg, reg)
@@ -304,8 +318,14 @@ TEST_F(BytecodeArrayBuilderTest, AllBytecodesGenerated) {
       .CreateObjectLiteral(factory->NewFixedArray(2), 0, 0);
 
   // Longer jumps requiring ConstantWide operand
-  builder.Jump(&start).JumpIfNull(&start).JumpIfUndefined(&start).JumpIfNotHole(
-      &start);
+  {
+    BytecodeLabel after_jump;
+    builder.Jump(&start)
+        .Bind(&after_jump)
+        .JumpIfNull(&start)
+        .JumpIfUndefined(&start)
+        .JumpIfNotHole(&start);
+  }
 
   // Perform an operation that returns boolean value to
   // generate JumpIfTrue/False
@@ -506,8 +526,10 @@ TEST_F(BytecodeArrayBuilderTest, ForwardJumps) {
   Register reg(0);
   BytecodeLabel far0, far1, far2, far3, far4;
   BytecodeLabel near0, near1, near2, near3, near4;
+  BytecodeLabel after_jump0, after_jump1;
 
   builder.Jump(&near0)
+      .Bind(&after_jump0)
       .CompareOperation(Token::Value::EQ, reg)
       .JumpIfTrue(&near1)
       .CompareOperation(Token::Value::EQ, reg)
@@ -522,6 +544,7 @@ TEST_F(BytecodeArrayBuilderTest, ForwardJumps) {
       .Bind(&near3)
       .Bind(&near4)
       .Jump(&far0)
+      .Bind(&after_jump1)
       .CompareOperation(Token::Value::EQ, reg)
       .JumpIfTrue(&far1)
       .CompareOperation(Token::Value::EQ, reg)
@@ -637,7 +660,8 @@ TEST_F(BytecodeArrayBuilderTest, BackwardJumps) {
       .BinaryOperation(Token::Value::ADD, reg)
       .JumpIfFalse(&label4);
   for (int i = 0; i < 63; i++) {
-    builder.Jump(&label4);
+    BytecodeLabel after_jump;
+    builder.Jump(&label4).Bind(&after_jump);
   }
 
   // Add padding to force wide backwards jumps.
@@ -650,6 +674,8 @@ TEST_F(BytecodeArrayBuilderTest, BackwardJumps) {
   builder.CompareOperation(Token::Value::EQ, reg).JumpIfFalse(&label2);
   builder.CompareOperation(Token::Value::EQ, reg).JumpIfTrue(&label1);
   builder.Jump(&label0);
+  BytecodeLabel end;
+  builder.Bind(&end);
   builder.Return();
 
   Handle<BytecodeArray> array = builder.ToBytecodeArray();
@@ -735,9 +761,15 @@ TEST_F(BytecodeArrayBuilderTest, LabelReuse) {
 
   // Labels can only have 1 forward reference, but
   // can be referred to mulitple times once bound.
-  BytecodeLabel label;
-
-  builder.Jump(&label).Bind(&label).Jump(&label).Jump(&label).Return();
+  BytecodeLabel label, after_jump0, after_jump1;
+
+  builder.Jump(&label)
+      .Bind(&label)
+      .Jump(&label)
+      .Bind(&after_jump0)
+      .Jump(&label)
+      .Bind(&after_jump1)
+      .Return();
 
   Handle<BytecodeArray> array = builder.ToBytecodeArray();
   BytecodeArrayIterator iterator(array);
@@ -761,8 +793,13 @@ TEST_F(BytecodeArrayBuilderTest, LabelAddressReuse) {
 
   BytecodeArrayBuilder builder(isolate(), zone(), 0, 0, 0);
   for (int i = 0; i < kRepeats; i++) {
-    BytecodeLabel label;
-    builder.Jump(&label).Bind(&label).Jump(&label).Jump(&label);
+    BytecodeLabel label, after_jump0, after_jump1;
+    builder.Jump(&label)
+        .Bind(&label)
+        .Jump(&label)
+        .Bind(&after_jump0)
+        .Jump(&label)
+        .Bind(&after_jump1);
   }
   builder.Return();
 

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

test/unittests/unittests.gyp

@@ -100,6 +100,7 @@
         'interpreter/bytecode-array-builder-unittest.cc',
         'interpreter/bytecode-array-iterator-unittest.cc',
         'interpreter/bytecode-array-writer-unittest.cc',
+        'interpreter/bytecode-dead-code-optimizer-unittest.cc',
         'interpreter/bytecode-peephole-optimizer-unittest.cc',
         'interpreter/bytecode-pipeline-unittest.cc',
         'interpreter/bytecode-register-allocator-unittest.cc',