[esnext] re-implement template strings

- Add a new bytecode for the ToString operation, replacing the old
intrinsic call (currently does not collect type feedback).
- Add a new AST node to represent TemplateLiterals, and avoid
generating unnecessary ToString operations in some simple cases.
- Use a single feedback slot for each string addition, because the
type feedback should always be the same for each addition

This seems to produce a very slight improvement on JSTests benchmarks
and bench-ruben.js from v8:7415, and it's possible that type feedback
for the ToString bytecode could provide more opportunities to eliminate
the runtime call in TurboFan.

Doesn't touch tagged templates

BUG=v8:7415
R=rmcilroy@chromium.org, ishell@chromium.org, bmeurer@chromium.org

Change-Id: If5a8c68558431f058db894d65776324abf54218e
Reviewed-on: https://chromium-review.googlesource.com/945408Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Caitlin Potter <caitp@igalia.com>
Cr-Commit-Position: refs/heads/master@{#51853}

src/ast/ast-traversal-visitor.h

@@ -535,6 +535,15 @@ void AstTraversalVisitor<Subclass>::VisitGetTemplateObject(
   PROCESS_EXPRESSION(expr);
 }
 
+template <class Subclass>
+void AstTraversalVisitor<Subclass>::VisitTemplateLiteral(
+    TemplateLiteral* expr) {
+  PROCESS_EXPRESSION(expr);
+  for (Expression* sub : *expr->substitutions()) {
+    RECURSE_EXPRESSION(Visit(sub));
+  }
+}
+
 template <class Subclass>
 void AstTraversalVisitor<Subclass>::VisitImportCallExpression(
     ImportCallExpression* expr) {

src/ast/ast.h

@@ -99,6 +99,7 @@ namespace internal {
   V(Spread)                     \
   V(SuperCallReference)         \
   V(SuperPropertyReference)     \
+  V(TemplateLiteral)            \
   V(ThisFunction)               \
   V(Throw)                      \
   V(UnaryOperation)             \
@@ -2653,6 +2654,26 @@ class GetTemplateObject final : public Expression {
   const ZoneList<const AstRawString*>* raw_strings_;
 };
 
+class TemplateLiteral final : public Expression {
+ public:
+  using StringList = ZoneList<const AstRawString*>;
+  using ExpressionList = ZoneList<Expression*>;
+
+  const StringList* string_parts() const { return string_parts_; }
+  const ExpressionList* substitutions() const { return substitutions_; }
+
+ private:
+  friend class AstNodeFactory;
+  TemplateLiteral(const StringList* parts, const ExpressionList* substitutions,
+                  int pos)
+      : Expression(pos, kTemplateLiteral),
+        string_parts_(parts),
+        substitutions_(substitutions) {}
+
+  const StringList* string_parts_;
+  const ExpressionList* substitutions_;
+};
+
 // ----------------------------------------------------------------------------
 // Basic visitor
 // Sub-class should parametrize AstVisitor with itself, e.g.:
@@ -3229,6 +3250,12 @@ class AstNodeFactory final BASE_EMBEDDED {
     return new (zone_) GetTemplateObject(cooked_strings, raw_strings, pos);
   }
 
+  TemplateLiteral* NewTemplateLiteral(
+      const ZoneList<const AstRawString*>* string_parts,
+      const ZoneList<Expression*>* substitutions, int pos) {
+    return new (zone_) TemplateLiteral(string_parts, substitutions, pos);
+  }
+
   ImportCallExpression* NewImportCallExpression(Expression* args, int pos) {
     return new (zone_) ImportCallExpression(args, pos);
   }

src/ast/prettyprinter.cc

@@ -466,6 +466,26 @@ void CallPrinter::VisitGetIterator(GetIterator* node) {
 
 void CallPrinter::VisitGetTemplateObject(GetTemplateObject* node) {}
 
+void CallPrinter::VisitTemplateLiteral(TemplateLiteral* node) {
+  if (node->substitutions()->length() && node->position() < position_ &&
+      node->substitutions()->last()->position() <= position_) {
+    found_ = true;
+    Print("`...${");
+    for (Expression* sub : *node->substitutions()) {
+      if (sub->position() < position_) continue;
+      Find(sub, true);
+    }
+    Print("}...`");
+    done_ = true;
+  } else if (node->string_parts()->length() == 1) {
+    Print("`");
+    PrintLiteral(node->string_parts()->first(), false);
+    Print("`");
+  } else {
+    Print("`...`");
+  }
+}
+
 void CallPrinter::VisitImportCallExpression(ImportCallExpression* node) {
   Print("ImportCall(");
   Find(node->argument(), true);
@@ -1332,6 +1352,17 @@ void AstPrinter::VisitGetTemplateObject(GetTemplateObject* node) {
   IndentedScope indent(this, "GET-TEMPLATE-OBJECT", node->position());
 }
 
+void AstPrinter::VisitTemplateLiteral(TemplateLiteral* node) {
+  IndentedScope indent(this, "TEMPLATE-LITERAL", node->position());
+  const AstRawString* string = node->string_parts()->first();
+  if (!string->IsEmpty()) PrintLiteralIndented("SPAN", string, true);
+  for (int i = 0; i < node->string_parts()->length();) {
+    PrintIndentedVisit("EXPR", node->substitutions()->at(i++));
+    string = node->string_parts()->at(i);
+    if (!string->IsEmpty()) PrintLiteralIndented("SPAN", string, true);
+  }
+}
+
 void AstPrinter::VisitImportCallExpression(ImportCallExpression* node) {
   IndentedScope indent(this, "IMPORT-CALL", node->position());
   Visit(node->argument());

src/compiler/bytecode-graph-builder.cc

@@ -2528,6 +2528,12 @@ void BytecodeGraphBuilder::VisitToObject() {
   BuildCastOperator(javascript()->ToObject());
 }
 
+void BytecodeGraphBuilder::VisitToString() {
+  Node* value =
+      NewNode(javascript()->ToString(), environment()->LookupAccumulator());
+  environment()->BindAccumulator(value, Environment::kAttachFrameState);
+}
+
 void BytecodeGraphBuilder::VisitToNumber() {
   PrepareEagerCheckpoint();
   Node* object = environment()->LookupAccumulator();

src/debug/debug-evaluate.cc

@@ -507,6 +507,7 @@ bool BytecodeHasNoSideEffect(interpreter::Bytecode bytecode) {
     case Bytecode::kToObject:
     case Bytecode::kToNumber:
     case Bytecode::kToName:
+    case Bytecode::kToString:
     // Misc.
     case Bytecode::kForInEnumerate:
     case Bytecode::kForInPrepare:

src/interpreter/bytecode-array-builder.cc

@@ -1004,6 +1004,11 @@ BytecodeArrayBuilder& BytecodeArrayBuilder::ToName(Register out) {
   return *this;
 }
 
+BytecodeArrayBuilder& BytecodeArrayBuilder::ToString() {
+  OutputToString();
+  return *this;
+}
+
 BytecodeArrayBuilder& BytecodeArrayBuilder::ToNumber(int feedback_slot) {
   OutputToNumber(feedback_slot);
   return *this;

src/interpreter/bytecode-array-builder.h

@@ -376,6 +376,7 @@ class V8_EXPORT_PRIVATE BytecodeArrayBuilder final {
   // Converts accumulator and stores result in register |out|.
   BytecodeArrayBuilder& ToObject(Register out);
   BytecodeArrayBuilder& ToName(Register out);
+  BytecodeArrayBuilder& ToString();
 
   // Converts accumulator and stores result back in accumulator.
   BytecodeArrayBuilder& ToNumber(int feedback_slot);

src/interpreter/bytecode-generator.cc

@@ -593,6 +593,11 @@ class BytecodeGenerator::ExpressionResultScope {
     type_hint_ = TypeHint::kBoolean;
   }
 
+  void SetResultIsString() {
+    DCHECK_EQ(type_hint_, TypeHint::kAny);
+    type_hint_ = TypeHint::kString;
+  }
+
   TypeHint type_hint() const { return type_hint_; }
 
  private:
@@ -2057,6 +2062,7 @@ void BytecodeGenerator::VisitLiteral(Literal* expr) {
       break;
     case Literal::kString:
       builder()->LoadLiteral(expr->AsRawString());
+      execution_result()->SetResultIsString();
       break;
     case Literal::kSymbol:
       builder()->LoadLiteral(expr->AsSymbol());
@@ -3982,13 +3988,23 @@ void BytecodeGenerator::VisitArithmeticExpression(BinaryOperation* expr) {
   Expression* subexpr;
   Smi* literal;
   if (expr->IsSmiLiteralOperation(&subexpr, &literal)) {
-    VisitForAccumulatorValue(subexpr);
+    TypeHint type_hint = VisitForAccumulatorValue(subexpr);
     builder()->SetExpressionPosition(expr);
     builder()->BinaryOperationSmiLiteral(expr->op(), literal,
                                          feedback_index(slot));
+    if (expr->op() == Token::ADD && type_hint == TypeHint::kString) {
+      execution_result()->SetResultIsString();
+    }
   } else {
-    Register lhs = VisitForRegisterValue(expr->left());
-    VisitForAccumulatorValue(expr->right());
+    TypeHint lhs_type = VisitForAccumulatorValue(expr->left());
+    Register lhs = register_allocator()->NewRegister();
+    builder()->StoreAccumulatorInRegister(lhs);
+    TypeHint rhs_type = VisitForAccumulatorValue(expr->right());
+    if (expr->op() == Token::ADD &&
+        (lhs_type == TypeHint::kString || rhs_type == TypeHint::kString)) {
+      execution_result()->SetResultIsString();
+    }
+
     builder()->SetExpressionPosition(expr);
     builder()->BinaryOperation(expr->op(), lhs, feedback_index(slot));
   }
@@ -3996,7 +4012,7 @@ void BytecodeGenerator::VisitArithmeticExpression(BinaryOperation* expr) {
 
 void BytecodeGenerator::VisitNaryArithmeticExpression(NaryOperation* expr) {
   // TODO(leszeks): Add support for lhs smi in commutative ops.
-  VisitForAccumulatorValue(expr->first());
+  TypeHint type_hint = VisitForAccumulatorValue(expr->first());
 
   for (size_t i = 0; i < expr->subsequent_length(); ++i) {
     RegisterAllocationScope register_scope(this);
@@ -4008,13 +4024,19 @@ void BytecodeGenerator::VisitNaryArithmeticExpression(NaryOperation* expr) {
     } else {
       Register lhs = register_allocator()->NewRegister();
       builder()->StoreAccumulatorInRegister(lhs);
-      VisitForAccumulatorValue(expr->subsequent(i));
+      TypeHint rhs_hint = VisitForAccumulatorValue(expr->subsequent(i));
+      if (rhs_hint == TypeHint::kString) type_hint = TypeHint::kString;
       builder()->SetExpressionPosition(expr->subsequent_op_position(i));
       builder()->BinaryOperation(
           expr->op(), lhs,
           feedback_index(feedback_spec()->AddBinaryOpICSlot()));
     }
   }
+
+  if (type_hint == TypeHint::kString && expr->op() == Token::ADD) {
+    // If any operand of an ADD is a String, a String is produced.
+    execution_result()->SetResultIsString();
+  }
 }
 
 void BytecodeGenerator::VisitSpread(Spread* expr) { Visit(expr->expression()); }
@@ -4195,6 +4217,53 @@ void BytecodeGenerator::VisitGetTemplateObject(GetTemplateObject* expr) {
   builder()->GetTemplateObject(entry, feedback_index(literal_slot));
 }
 
+void BytecodeGenerator::VisitTemplateLiteral(TemplateLiteral* expr) {
+  const TemplateLiteral::StringList& parts = *expr->string_parts();
+  const TemplateLiteral::ExpressionList& substitutions = *expr->substitutions();
+  // Template strings with no substitutions are turned into StringLiterals.
+  DCHECK_GT(substitutions.length(), 0);
+  DCHECK_EQ(parts.length(), substitutions.length() + 1);
+
+  // Generate string concatenation
+  // TODO(caitp): Don't generate feedback slot if it's not used --- introduce
+  // a simple, concise, reusable mechanism to lazily create reusable slots.
+  FeedbackSlot slot = feedback_spec()->AddBinaryOpICSlot();
+  Register last_part = register_allocator()->NewRegister();
+  bool last_part_valid = false;
+
+  builder()->SetExpressionPosition(expr);
+  for (int i = 0; i < substitutions.length(); ++i) {
+    if (i != 0) {
+      builder()->StoreAccumulatorInRegister(last_part);
+      last_part_valid = true;
+    }
+
+    if (!parts[i]->IsEmpty()) {
+      builder()->LoadLiteral(parts[i]);
+      if (last_part_valid) {
+        builder()->BinaryOperation(Token::ADD, last_part, feedback_index(slot));
+      }
+      builder()->StoreAccumulatorInRegister(last_part);
+      last_part_valid = true;
+    }
+
+    TypeHint type_hint = VisitForAccumulatorValue(substitutions[i]);
+    if (type_hint != TypeHint::kString) {
+      builder()->ToString();
+    }
+    if (last_part_valid) {
+      builder()->BinaryOperation(Token::ADD, last_part, feedback_index(slot));
+    }
+    last_part_valid = false;
+  }
+
+  if (!parts.last()->IsEmpty()) {
+    builder()->StoreAccumulatorInRegister(last_part);
+    builder()->LoadLiteral(parts.last());
+    builder()->BinaryOperation(Token::ADD, last_part, feedback_index(slot));
+  }
+}
+
 void BytecodeGenerator::VisitThisFunction(ThisFunction* expr) {
   builder()->LoadAccumulatorWithRegister(Register::function_closure());
 }

src/interpreter/bytecode-generator.h

@@ -66,7 +66,7 @@ class BytecodeGenerator final : public AstVisitor<BytecodeGenerator> {
   using ToBooleanMode = BytecodeArrayBuilder::ToBooleanMode;
 
   enum class TestFallthrough { kThen, kElse, kNone };
-  enum class TypeHint { kAny, kBoolean };
+  enum class TypeHint { kAny, kBoolean, kString };
 
   void GenerateBytecodeBody();
   void AllocateDeferredConstants(Isolate* isolate, Handle<Script> script);

src/interpreter/bytecodes.h

@@ -223,6 +223,7 @@ namespace interpreter {
   V(ToNumber, AccumulatorUse::kReadWrite, OperandType::kIdx)                   \
   V(ToNumeric, AccumulatorUse::kReadWrite, OperandType::kIdx)                  \
   V(ToObject, AccumulatorUse::kRead, OperandType::kRegOut)                     \
+  V(ToString, AccumulatorUse::kReadWrite)                                      \
                                                                                \
   /* Literals */                                                               \
   V(CreateRegExpLiteral, AccumulatorUse::kWrite, OperandType::kIdx,            \

src/interpreter/interpreter-generator.cc

@@ -1304,6 +1304,14 @@ IGNITION_HANDLER(ToObject, InterpreterAssembler) {
   Dispatch();
 }
 
+// ToString
+//
+// Convert the accumulator to a String.
+IGNITION_HANDLER(ToString, InterpreterAssembler) {
+  SetAccumulator(ToString_Inline(GetContext(), GetAccumulator()));
+  Dispatch();
+}
+
 class IncDecAssembler : public UnaryNumericOpAssembler {
  public:
   explicit IncDecAssembler(CodeAssemblerState* state, Bytecode bytecode,

src/parsing/parser.cc

@@ -3492,52 +3492,10 @@ Expression* Parser::CloseTemplateLiteral(TemplateLiteralState* state, int start,
   DCHECK_EQ(cooked_strings->length(), expressions->length() + 1);
 
   if (!tag) {
-    const AstRawString* first_string = cooked_strings->at(0);
-    if (expressions->length() == 0) {
-      return factory()->NewStringLiteral(first_string, kNoSourcePosition);
+    if (cooked_strings->length() == 1) {
+      return factory()->NewStringLiteral(cooked_strings->first(), pos);
     }
-
-    size_t num_empty =
-        std::count_if(cooked_strings->begin(), cooked_strings->end(),
-                      [=](const AstRawString* lit) { return lit->IsEmpty(); });
-
-    const bool kFirstIsEmpty = first_string->IsEmpty();
-    Expression* first = kFirstIsEmpty ? ToString(expressions->at(0))
-                                      : factory()->NewStringLiteral(
-                                            first_string, kNoSourcePosition);
-
-    // Build N-ary addition op to simplify code-generation.
-    // TODO(leszeks): Could we just store this expression in the
-    // TemplateLiteralState and build it as we go?
-    NaryOperation* expr = factory()->NewNaryOperation(
-        Token::ADD, first, 2 * expressions->length() - num_empty);
-
-    int i = 0;
-    if (kFirstIsEmpty) {
-      // If the first string is empty, possibly add the next template span
-      // outside of the loop, to keep the loop logic simple.
-      i = 1;
-      const AstRawString* str = cooked_strings->at(1);
-      if (!str->IsEmpty()) {
-        expr->AddSubsequent(factory()->NewStringLiteral(str, kNoSourcePosition),
-                            first->position());
-      }
-    }
-
-    while (i < expressions->length()) {
-      Expression* sub = expressions->at(i++);
-      const AstRawString* cooked_str = cooked_strings->at(i);
-      DCHECK_NOT_NULL(cooked_str);
-
-      // Let middle be ToString(sub).
-      expr->AddSubsequent(ToString(sub), sub->position());
-      if (!cooked_str->IsEmpty()) {
-        expr->AddSubsequent(
-            factory()->NewStringLiteral(cooked_str, kNoSourcePosition),
-            sub->position());
-      }
-    }
-    return expr;
+    return factory()->NewTemplateLiteral(cooked_strings, expressions, pos);
   } else {
     // GetTemplateObject
     Expression* template_object =

src/parsing/pattern-rewriter.cc

@@ -772,6 +772,7 @@ NOT_A_PATTERN(Spread)
 NOT_A_PATTERN(SuperPropertyReference)
 NOT_A_PATTERN(SuperCallReference)
 NOT_A_PATTERN(SwitchStatement)
+NOT_A_PATTERN(TemplateLiteral)
 NOT_A_PATTERN(ThisFunction)
 NOT_A_PATTERN(Throw)
 NOT_A_PATTERN(TryCatchStatement)

test/cctest/interpreter/bytecode_expectations/TemplateLiterals.golden

@@ -13,20 +13,22 @@ snippet: "
 "
 frame size: 3
 parameter count: 1
-bytecode array length: 30
+bytecode array length: 28
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(LdaSmi), I8(1),
                 B(Star), R(0),
   /*   53 S> */ B(LdaSmi), I8(2),
                 B(Star), R(1),
-  /*   56 S> */ B(InvokeIntrinsic), U8(Runtime::k_ToString), R(0), U8(1),
+  /*   56 S> */ B(Ldar), R(0),
+                B(ToString),
                 B(Star), R(2),
-  /*   70 E> */ B(InvokeIntrinsic), U8(Runtime::k_ToString), R(1), U8(1),
-  /*   70 E> */ B(Add), R(2), U8(0),
+                B(Ldar), R(1),
+  /*   70 E> */ B(ToString),
+                B(Add), R(2), U8(0),
                 B(Star), R(2),
                 B(LdaConstant), U8(0),
-  /*   70 E> */ B(Add), R(2), U8(1),
+                B(Add), R(2), U8(0),
   /*   80 S> */ B(Return),
 ]
 constant pool: [
@@ -43,7 +45,7 @@ snippet: "
 "
 frame size: 3
 parameter count: 1
-bytecode array length: 30
+bytecode array length: 28
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(LdaSmi), I8(1),
@@ -52,11 +54,13 @@ bytecodes: [
                 B(Star), R(1),
   /*   56 S> */ B(LdaConstant), U8(0),
                 B(Star), R(2),
-  /*   72 E> */ B(InvokeIntrinsic), U8(Runtime::k_ToString), R(0), U8(1),
-  /*   72 E> */ B(Add), R(2), U8(0),
+                B(Ldar), R(0),
+  /*   72 E> */ B(ToString),
+                B(Add), R(2), U8(0),
                 B(Star), R(2),
-  /*   76 E> */ B(InvokeIntrinsic), U8(Runtime::k_ToString), R(1), U8(1),
-  /*   76 E> */ B(Add), R(2), U8(1),
+                B(Ldar), R(1),
+  /*   76 E> */ B(ToString),
+                B(Add), R(2), U8(0),
   /*   80 S> */ B(Return),
 ]
 constant pool: [
@@ -73,20 +77,22 @@ snippet: "
 "
 frame size: 3
 parameter count: 1
-bytecode array length: 30
+bytecode array length: 28
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(LdaSmi), I8(1),
                 B(Star), R(0),
   /*   53 S> */ B(LdaSmi), I8(2),
                 B(Star), R(1),
-  /*   56 S> */ B(InvokeIntrinsic), U8(Runtime::k_ToString), R(0), U8(1),
+  /*   56 S> */ B(Ldar), R(0),
+                B(ToString),
                 B(Star), R(2),
                 B(LdaConstant), U8(0),
-  /*   66 E> */ B(Add), R(2), U8(0),
+                B(Add), R(2), U8(0),
                 B(Star), R(2),
-  /*   76 E> */ B(InvokeIntrinsic), U8(Runtime::k_ToString), R(1), U8(1),
-  /*   76 E> */ B(Add), R(2), U8(1),
+                B(Ldar), R(1),
+  /*   76 E> */ B(ToString),
+                B(Add), R(2), U8(0),
   /*   80 S> */ B(Return),
 ]
 constant pool: [
@@ -101,9 +107,9 @@ snippet: "
   var b = 2;
   return `foo${a}bar${b}baz${1}`;
 "
-frame size: 4
+frame size: 3
 parameter count: 1
-bytecode array length: 57
+bytecode array length: 50
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(LdaSmi), I8(1),
@@ -112,22 +118,23 @@ bytecodes: [
                 B(Star), R(1),
   /*   56 S> */ B(LdaConstant), U8(0),
                 B(Star), R(2),
-  /*   69 E> */ B(InvokeIntrinsic), U8(Runtime::k_ToString), R(0), U8(1),
-  /*   69 E> */ B(Add), R(2), U8(0),
+                B(Ldar), R(0),
+  /*   69 E> */ B(ToString),
+                B(Add), R(2), U8(0),
                 B(Star), R(2),
                 B(LdaConstant), U8(1),
-  /*   69 E> */ B(Add), R(2), U8(1),
+                B(Add), R(2), U8(0),
                 B(Star), R(2),
-  /*   76 E> */ B(InvokeIntrinsic), U8(Runtime::k_ToString), R(1), U8(1),
-  /*   76 E> */ B(Add), R(2), U8(2),
+                B(Ldar), R(1),
+  /*   76 E> */ B(ToString),
+                B(Add), R(2), U8(0),
                 B(Star), R(2),
                 B(LdaConstant), U8(2),
-  /*   76 E> */ B(Add), R(2), U8(3),
+                B(Add), R(2), U8(0),
                 B(Star), R(2),
                 B(LdaSmi), I8(1),
-                B(Star), R(3),
-                B(InvokeIntrinsic), U8(Runtime::k_ToString), R(3), U8(1),
-  /*   83 E> */ B(Add), R(2), U8(4),
+                B(ToString),
+                B(Add), R(2), U8(0),
   /*   87 S> */ B(Return),
 ]
 constant pool: [
@@ -146,23 +153,25 @@ snippet: "
 "
 frame size: 4
 parameter count: 1
-bytecode array length: 37
+bytecode array length: 35
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(LdaSmi), I8(1),
                 B(Star), R(0),
   /*   53 S> */ B(LdaSmi), I8(2),
                 B(Star), R(1),
-  /*   56 S> */ B(InvokeIntrinsic), U8(Runtime::k_ToString), R(0), U8(1),
+  /*   56 S> */ B(Ldar), R(0),
+                B(ToString),
                 B(Star), R(2),
                 B(LdaConstant), U8(0),
-  /*   66 E> */ B(Add), R(2), U8(0),
+                B(Add), R(2), U8(1),
                 B(Star), R(2),
                 B(LdaConstant), U8(0),
                 B(Star), R(3),
-  /*   87 E> */ B(InvokeIntrinsic), U8(Runtime::k_ToString), R(1), U8(1),
-  /*   87 E> */ B(Add), R(3), U8(1),
-  /*   76 E> */ B(Add), R(2), U8(2),
+                B(Ldar), R(1),
+  /*   87 E> */ B(ToString),
+                B(Add), R(3), U8(2),
+  /*   76 E> */ B(Add), R(2), U8(0),
   /*   91 S> */ B(Return),
 ]
 constant pool: [
@@ -178,9 +187,9 @@ snippet: "
   function foo(a, b) { };
   return `string${foo(a, b)}${a}${b}`;
 "
-frame size: 5
+frame size: 4
 parameter count: 1
-bytecode array length: 52
+bytecode array length: 45
 bytecodes: [
                 B(CreateClosure), U8(0), U8(0), U8(2),
                 B(Star), R(2),
@@ -191,16 +200,17 @@ bytecodes: [
                 B(Star), R(1),
   /*   80 S> */ B(LdaConstant), U8(1),
                 B(Star), R(3),
-  /*   96 E> */ B(CallUndefinedReceiver2), R(2), R(0), R(1), U8(1),
-                B(Star), R(4),
-                B(InvokeIntrinsic), U8(Runtime::k_ToString), R(4), U8(1),
-  /*   96 E> */ B(Add), R(3), U8(3),
+  /*   96 E> */ B(CallUndefinedReceiver2), R(2), R(0), R(1), U8(2),
+                B(ToString),
+                B(Add), R(3), U8(1),
                 B(Star), R(3),
-  /*  108 E> */ B(InvokeIntrinsic), U8(Runtime::k_ToString), R(0), U8(1),
-  /*  108 E> */ B(Add), R(3), U8(4),
+                B(Ldar), R(0),
+  /*  108 E> */ B(ToString),
+                B(Add), R(3), U8(1),
                 B(Star), R(3),
-  /*  112 E> */ B(InvokeIntrinsic), U8(Runtime::k_ToString), R(1), U8(1),
-  /*  112 E> */ B(Add), R(3), U8(5),
+                B(Ldar), R(1),
+  /*  112 E> */ B(ToString),
+                B(Add), R(3), U8(1),
   /*  116 S> */ B(Return),
 ]
 constant pool: [

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

@@ -262,7 +262,7 @@ TEST_F(BytecodeArrayBuilderTest, AllBytecodesGenerated) {
       .CompareNull();
 
   // Emit conversion operator invocations.
-  builder.ToNumber(1).ToNumeric(1).ToObject(reg).ToName(reg);
+  builder.ToNumber(1).ToNumeric(1).ToObject(reg).ToName(reg).ToString();
 
   // Emit GetSuperConstructor.
   builder.GetSuperConstructor(reg);