[hydrogen] optimize switch with string clauses

Hydrogen should optimize not only SMI clauses, but clauses with string literals
too.

Patch from fedor.indutny <fedor.indutny@gmail.com>.

R=vegorov@chromium.org
BUG=
TEST=
Review URL: http://codereview.chromium.org/8373029

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9901 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/lithium-arm.cc

@@ -228,6 +228,13 @@ void LIsObjectAndBranch::PrintDataTo(StringStream* stream) {
 }
 
 
+void LIsStringAndBranch::PrintDataTo(StringStream* stream) {
+  stream->Add("if is_string(");
+  InputAt(0)->PrintTo(stream);
+  stream->Add(") then B%d else B%d", true_block_id(), false_block_id());
+}
+
+
 void LIsSmiAndBranch::PrintDataTo(StringStream* stream) {
   stream->Add("if is_smi(");
   InputAt(0)->PrintTo(stream);
@@ -242,6 +249,14 @@ void LIsUndetectableAndBranch::PrintDataTo(StringStream* stream) {
 }
 
 
+void LStringCompareAndBranch::PrintDataTo(StringStream* stream) {
+  stream->Add("if compare_generic(");
+  InputAt(0)->PrintTo(stream);
+  InputAt(1)->PrintTo(stream);
+  stream->Add(") then B%d else B%d", true_block_id(), false_block_id());
+}
+
+
 void LHasInstanceTypeAndBranch::PrintDataTo(StringStream* stream) {
   stream->Add("if has_instance_type(");
   InputAt(0)->PrintTo(stream);
@@ -1451,6 +1466,13 @@ LInstruction* LChunkBuilder::DoIsObjectAndBranch(HIsObjectAndBranch* instr) {
 }
 
 
+LInstruction* LChunkBuilder::DoIsStringAndBranch(HIsStringAndBranch* instr) {
+  ASSERT(instr->value()->representation().IsTagged());
+  LOperand* temp = TempRegister();
+  return new LIsStringAndBranch(UseRegisterAtStart(instr->value()), temp);
+}
+
+
 LInstruction* LChunkBuilder::DoIsSmiAndBranch(HIsSmiAndBranch* instr) {
   ASSERT(instr->value()->representation().IsTagged());
   return new LIsSmiAndBranch(Use(instr->value()));
@@ -1465,6 +1487,18 @@ LInstruction* LChunkBuilder::DoIsUndetectableAndBranch(
 }
 
 
+LInstruction* LChunkBuilder::DoStringCompareAndBranch(
+    HStringCompareAndBranch* instr) {
+
+  ASSERT(instr->left()->representation().IsTagged());
+  ASSERT(instr->right()->representation().IsTagged());
+  LOperand* left = UseFixed(instr->left(), r1);
+  LOperand* right = UseFixed(instr->right(), r0);
+  LStringCompareAndBranch* result = new LStringCompareAndBranch(left, right);
+  return MarkAsCall(result, instr);
+}
+
+
 LInstruction* LChunkBuilder::DoHasInstanceTypeAndBranch(
     HHasInstanceTypeAndBranch* instr) {
   ASSERT(instr->value()->representation().IsTagged());

src/arm/lithium-arm.h

@@ -109,8 +109,10 @@ class LCodeGen;
   V(IsConstructCallAndBranch)                   \
   V(IsNilAndBranch)                             \
   V(IsObjectAndBranch)                          \
+  V(IsStringAndBranch)                          \
   V(IsSmiAndBranch)                             \
   V(IsUndetectableAndBranch)                    \
+  V(StringCompareAndBranch)                    \
   V(JSArrayLength)                              \
   V(Label)                                      \
   V(LazyBailout)                                \
@@ -658,6 +660,20 @@ class LIsObjectAndBranch: public LControlInstruction<1, 1> {
 };
 
 
+class LIsStringAndBranch: public LControlInstruction<1, 1> {
+ public:
+  LIsStringAndBranch(LOperand* value, LOperand* temp) {
+    inputs_[0] = value;
+    temps_[0] = temp;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(IsStringAndBranch, "is-string-and-branch")
+  DECLARE_HYDROGEN_ACCESSOR(IsStringAndBranch)
+
+  virtual void PrintDataTo(StringStream* stream);
+};
+
+
 class LIsSmiAndBranch: public LControlInstruction<1, 0> {
  public:
   explicit LIsSmiAndBranch(LOperand* value) {
@@ -686,6 +702,23 @@ class LIsUndetectableAndBranch: public LControlInstruction<1, 1> {
 };
 
 
+class LStringCompareAndBranch: public LControlInstruction<2, 0> {
+ public:
+  LStringCompareAndBranch(LOperand* left, LOperand* right) {
+    inputs_[0] = left;
+    inputs_[1] = right;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(StringCompareAndBranch,
+                               "compare-generic-and-branch")
+  DECLARE_HYDROGEN_ACCESSOR(StringCompareAndBranch)
+
+  Token::Value op() const { return hydrogen()->token(); }
+
+  virtual void PrintDataTo(StringStream* stream);
+};
+
+
 class LHasInstanceTypeAndBranch: public LControlInstruction<1, 0> {
  public:
   explicit LHasInstanceTypeAndBranch(LOperand* value) {

src/arm/lithium-codegen-arm.cc

@@ -1858,6 +1858,33 @@ void LCodeGen::DoIsObjectAndBranch(LIsObjectAndBranch* instr) {
 }
 
 
+Condition LCodeGen::EmitIsString(Register input,
+                                 Register temp1,
+                                 Label* is_not_string,
+                                 Label* is_string) {
+  __ JumpIfSmi(input, is_not_string);
+  __ CompareObjectType(input, temp1, temp1, FIRST_NONSTRING_TYPE);
+
+  return lt;
+}
+
+
+void LCodeGen::DoIsStringAndBranch(LIsStringAndBranch* instr) {
+  Register reg = ToRegister(instr->InputAt(0));
+  Register temp1 = ToRegister(instr->TempAt(0));
+
+  int true_block = chunk_->LookupDestination(instr->true_block_id());
+  int false_block = chunk_->LookupDestination(instr->false_block_id());
+  Label* true_label = chunk_->GetAssemblyLabel(true_block);
+  Label* false_label = chunk_->GetAssemblyLabel(false_block);
+
+  Condition true_cond =
+      EmitIsString(reg, temp1, false_label, true_label);
+
+  EmitBranch(true_block, false_block, true_cond);
+}
+
+
 void LCodeGen::DoIsSmiAndBranch(LIsSmiAndBranch* instr) {
   int true_block = chunk_->LookupDestination(instr->true_block_id());
   int false_block = chunk_->LookupDestination(instr->false_block_id());
@@ -1883,6 +1910,41 @@ void LCodeGen::DoIsUndetectableAndBranch(LIsUndetectableAndBranch* instr) {
 }
 
 
+static Condition ComputeCompareCondition(Token::Value op) {
+  switch (op) {
+    case Token::EQ_STRICT:
+    case Token::EQ:
+      return eq;
+    case Token::LT:
+      return lt;
+    case Token::GT:
+      return gt;
+    case Token::LTE:
+      return le;
+    case Token::GTE:
+      return ge;
+    default:
+      UNREACHABLE();
+      return kNoCondition;
+  }
+}
+
+
+void LCodeGen::DoStringCompareAndBranch(LStringCompareAndBranch* instr) {
+  Token::Value op = instr->op();
+  int true_block = chunk_->LookupDestination(instr->true_block_id());
+  int false_block = chunk_->LookupDestination(instr->false_block_id());
+
+  Handle<Code> ic = CompareIC::GetUninitialized(op);
+  CallCode(ic, RelocInfo::CODE_TARGET, instr);
+  __ cmp(r0, Operand(0));  // This instruction also signals no smi code inlined.
+
+  Condition condition = ComputeCompareCondition(op);
+
+  EmitBranch(true_block, false_block, condition);
+}
+
+
 static InstanceType TestType(HHasInstanceTypeAndBranch* instr) {
   InstanceType from = instr->from();
   InstanceType to = instr->to();
@@ -2168,26 +2230,6 @@ void LCodeGen::DoDeferredLInstanceOfKnownGlobal(LInstanceOfKnownGlobal* instr,
 }
 
 
-static Condition ComputeCompareCondition(Token::Value op) {
-  switch (op) {
-    case Token::EQ_STRICT:
-    case Token::EQ:
-      return eq;
-    case Token::LT:
-      return lt;
-    case Token::GT:
-      return gt;
-    case Token::LTE:
-      return le;
-    case Token::GTE:
-      return ge;
-    default:
-      UNREACHABLE();
-      return kNoCondition;
-  }
-}
-
-
 void LCodeGen::DoCmpT(LCmpT* instr) {
   Token::Value op = instr->op();
 

src/arm/lithium-codegen-arm.h

@@ -285,6 +285,14 @@ class LCodeGen BASE_EMBEDDED {
                          Label* is_not_object,
                          Label* is_object);
 
+  // Emits optimized code for %_IsString(x).  Preserves input register.
+  // Returns the condition on which a final split to
+  // true and false label should be made, to optimize fallthrough.
+  Condition EmitIsString(Register input,
+                         Register temp1,
+                         Label* is_not_object,
+                         Label* is_object);
+
   // Emits optimized code for %_IsConstructCall().
   // Caller should branch on equal condition.
   void EmitIsConstructCall(Register temp1, Register temp2);

src/ast.cc

@@ -695,6 +695,10 @@ void CaseClause::RecordTypeFeedback(TypeFeedbackOracle* oracle) {
   TypeInfo info = oracle->SwitchType(this);
   if (info.IsSmi()) {
     compare_type_ = SMI_ONLY;
+  } else if (info.IsSymbol()) {
+    compare_type_ = SYMBOL_ONLY;
+  } else if (info.IsNonSymbol()) {
+    compare_type_ = STRING_ONLY;
   } else if (info.IsNonPrimitive()) {
     compare_type_ = OBJECT_ONLY;
   } else {

src/ast.h

@@ -684,6 +684,8 @@ class CaseClause: public ZoneObject {
   // Type feedback information.
   void RecordTypeFeedback(TypeFeedbackOracle* oracle);
   bool IsSmiCompare() { return compare_type_ == SMI_ONLY; }
+  bool IsSymbolCompare() { return compare_type_ == SYMBOL_ONLY; }
+  bool IsStringCompare() { return compare_type_ == STRING_ONLY; }
   bool IsObjectCompare() { return compare_type_ == OBJECT_ONLY; }
 
  private:
@@ -691,7 +693,13 @@ class CaseClause: public ZoneObject {
   Label body_target_;
   ZoneList<Statement*>* statements_;
   int position_;
-  enum CompareTypeFeedback { NONE, SMI_ONLY, OBJECT_ONLY };
+  enum CompareTypeFeedback {
+    NONE,
+    SMI_ONLY,
+    SYMBOL_ONLY,
+    STRING_ONLY,
+    OBJECT_ONLY
+  };
   CompareTypeFeedback compare_type_;
   int compare_id_;
   int entry_id_;

src/hydrogen-instructions.cc

@@ -1325,6 +1325,13 @@ void HCompareGeneric::PrintDataTo(StringStream* stream) {
 }
 
 
+void HStringCompareAndBranch::PrintDataTo(StringStream* stream) {
+  stream->Add(Token::Name(token()));
+  stream->Add(" ");
+  HControlInstruction::PrintDataTo(stream);
+}
+
+
 void HCompareIDAndBranch::PrintDataTo(StringStream* stream) {
   stream->Add(Token::Name(token()));
   stream->Add(" ");

src/hydrogen-instructions.h

@@ -118,8 +118,10 @@ class LChunkBuilder;
   V(IsConstructCallAndBranch)                  \
   V(IsNilAndBranch)                            \
   V(IsObjectAndBranch)                         \
+  V(IsStringAndBranch)                         \
   V(IsSmiAndBranch)                            \
   V(IsUndetectableAndBranch)                   \
+  V(StringCompareAndBranch)                   \
   V(JSArrayLength)                             \
   V(LeaveInlined)                              \
   V(LoadContextSlot)                           \
@@ -2715,6 +2717,18 @@ class HIsObjectAndBranch: public HUnaryControlInstruction {
   DECLARE_CONCRETE_INSTRUCTION(IsObjectAndBranch)
 };
 
+class HIsStringAndBranch: public HUnaryControlInstruction {
+ public:
+  explicit HIsStringAndBranch(HValue* value)
+    : HUnaryControlInstruction(value, NULL, NULL) { }
+
+  virtual Representation RequiredInputRepresentation(int index) {
+    return Representation::Tagged();
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(IsStringAndBranch)
+};
+
 
 class HIsSmiAndBranch: public HUnaryControlInstruction {
  public:
@@ -2745,6 +2759,42 @@ class HIsUndetectableAndBranch: public HUnaryControlInstruction {
 };
 
 
+class HStringCompareAndBranch: public HTemplateControlInstruction<2, 3> {
+ public:
+  HStringCompareAndBranch(HValue* context,
+                           HValue* left,
+                           HValue* right,
+                           Token::Value token)
+      : token_(token) {
+    ASSERT(Token::IsCompareOp(token));
+    SetOperandAt(0, context);
+    SetOperandAt(1, left);
+    SetOperandAt(2, right);
+    set_representation(Representation::Tagged());
+  }
+
+  HValue* context() { return OperandAt(0); }
+  HValue* left() { return OperandAt(1); }
+  HValue* right() { return OperandAt(2); }
+  Token::Value token() const { return token_; }
+
+  virtual void PrintDataTo(StringStream* stream);
+
+  virtual Representation RequiredInputRepresentation(int index) {
+    return Representation::Tagged();
+  }
+
+  Representation GetInputRepresentation() const {
+    return Representation::Tagged();
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(StringCompareAndBranch)
+
+ private:
+  Token::Value token_;
+};
+
+
 class HIsConstructCallAndBranch: public HTemplateControlInstruction<2, 0> {
  public:
   virtual Representation RequiredInputRepresentation(int index) {

src/hydrogen.cc

@@ -734,6 +734,7 @@ void HGraph::Postorder(HBasicBlock* block,
       Postorder(it.Current(), visited, order, block);
     }
   } else {
+    ASSERT(block->IsFinished());
     for (HSuccessorIterator it(block->end()); !it.Done(); it.Advance()) {
       Postorder(it.Current(), visited, order, loop_header);
     }
@@ -2708,43 +2709,95 @@ void HGraphBuilder::VisitSwitchStatement(SwitchStatement* stmt) {
     return Bailout("SwitchStatement: too many clauses");
   }
 
+  HValue* context = environment()->LookupContext();
+
   CHECK_ALIVE(VisitForValue(stmt->tag()));
   AddSimulate(stmt->EntryId());
   HValue* tag_value = Pop();
   HBasicBlock* first_test_block = current_block();
 
-  // 1. Build all the tests, with dangling true branches.  Unconditionally
-  // deoptimize if we encounter a non-smi comparison.
+  SwitchType switch_type = UNKNOWN_SWITCH;
+
+  // 1. Extract clause type
   for (int i = 0; i < clause_count; ++i) {
     CaseClause* clause = clauses->at(i);
     if (clause->is_default()) continue;
-    if (!clause->label()->IsSmiLiteral()) {
-      return Bailout("SwitchStatement: non-literal switch label");
+
+    if (switch_type == UNKNOWN_SWITCH) {
+      if (clause->label()->IsSmiLiteral()) {
+        switch_type = SMI_SWITCH;
+      } else if (clause->label()->IsStringLiteral()) {
+        switch_type = STRING_SWITCH;
+      } else {
+        return Bailout("SwitchStatement: non-literal switch label");
+      }
+    } else if ((switch_type == STRING_SWITCH &&
+                !clause->label()->IsStringLiteral()) ||
+               (switch_type == SMI_SWITCH &&
+                !clause->label()->IsSmiLiteral())) {
+      return Bailout("SwitchStatemnt: mixed label types are not supported");
     }
+  }
 
-    // Unconditionally deoptimize on the first non-smi compare.
-    clause->RecordTypeFeedback(oracle());
-    if (!clause->IsSmiCompare()) {
-      // Finish with deoptimize and add uses of enviroment values to
-      // account for invisible uses.
-      current_block()->FinishExitWithDeoptimization(HDeoptimize::kUseAll);
-      set_current_block(NULL);
-      break;
+  HUnaryControlInstruction* string_check = NULL;
+  HBasicBlock* not_string_block = NULL;
+
+  // Test switch's tag value if all clauses are string literals
+  if (switch_type == STRING_SWITCH) {
+    string_check = new(zone()) HIsStringAndBranch(tag_value);
+    first_test_block = graph()->CreateBasicBlock();
+    not_string_block = graph()->CreateBasicBlock();
+
+    string_check->SetSuccessorAt(0, first_test_block);
+    string_check->SetSuccessorAt(1, not_string_block);
+    current_block()->Finish(string_check);
+
+    set_current_block(first_test_block);
+  }
+
+  // 2. Build all the tests, with dangling true branches
+  for (int i = 0; i < clause_count; ++i) {
+    CaseClause* clause = clauses->at(i);
+    if (clause->is_default()) continue;
+
+    if (switch_type == SMI_SWITCH) {
+      clause->RecordTypeFeedback(oracle());
     }
 
-    // Otherwise generate a compare and branch.
+    // Generate a compare and branch.
     CHECK_ALIVE(VisitForValue(clause->label()));
     HValue* label_value = Pop();
-    HCompareIDAndBranch* compare =
-        new(zone()) HCompareIDAndBranch(tag_value,
-                                        label_value,
-                                        Token::EQ_STRICT);
-    compare->SetInputRepresentation(Representation::Integer32());
-    HBasicBlock* body_block = graph()->CreateBasicBlock();
+
     HBasicBlock* next_test_block = graph()->CreateBasicBlock();
+    HBasicBlock* body_block = graph()->CreateBasicBlock();
+
+    HControlInstruction* compare;
+
+    if (switch_type == SMI_SWITCH) {
+      if (!clause->IsSmiCompare()) {
+        // Finish with deoptimize and add uses of enviroment values to
+        // account for invisible uses.
+        current_block()->FinishExitWithDeoptimization(HDeoptimize::kUseAll);
+        set_current_block(NULL);
+        break;
+      }
+
+      HCompareIDAndBranch* compare_ =
+          new(zone()) HCompareIDAndBranch(tag_value,
+                                          label_value,
+                                          Token::EQ_STRICT);
+      compare_->SetInputRepresentation(Representation::Integer32());
+      compare = compare_;
+    } else {
+      compare = new(zone()) HStringCompareAndBranch(context, tag_value,
+                                                     label_value,
+                                                     Token::EQ_STRICT);
+    }
+
     compare->SetSuccessorAt(0, body_block);
     compare->SetSuccessorAt(1, next_test_block);
     current_block()->Finish(compare);
+
     set_current_block(next_test_block);
   }
 
@@ -2752,10 +2805,15 @@ void HGraphBuilder::VisitSwitchStatement(SwitchStatement* stmt) {
   // exit.  This block is NULL if we deoptimized.
   HBasicBlock* last_block = current_block();
 
-  // 2. Loop over the clauses and the linked list of tests in lockstep,
+  if (not_string_block != NULL) {
+    last_block = CreateJoin(last_block, not_string_block, stmt->ExitId());
+  }
+
+  // 3. Loop over the clauses and the linked list of tests in lockstep,
   // translating the clause bodies.
   HBasicBlock* curr_test_block = first_test_block;
   HBasicBlock* fall_through_block = NULL;
+
   BreakAndContinueInfo break_info(stmt);
   { BreakAndContinueScope push(&break_info, this);
     for (int i = 0; i < clause_count; ++i) {

src/hydrogen.h

@@ -657,6 +657,7 @@ class FunctionState {
 class HGraphBuilder: public AstVisitor {
  public:
   enum BreakType { BREAK, CONTINUE };
+  enum SwitchType { UNKNOWN_SWITCH, SMI_SWITCH, STRING_SWITCH };
 
   // A class encapsulating (lazily-allocated) break and continue blocks for
   // a breakable statement.  Separated from BreakAndContinueScope so that it

src/ia32/lithium-codegen-ia32.cc

@@ -1716,6 +1716,33 @@ void LCodeGen::DoIsObjectAndBranch(LIsObjectAndBranch* instr) {
 }
 
 
+Condition LCodeGen::EmitIsString(Register input,
+                                 Register temp1,
+                                 Label* is_not_string,
+                                 Label* is_string) {
+  __ JumpIfSmi(input, is_not_string);
+
+  Condition cond = masm_->IsObjectStringType(input, temp1, temp1);
+
+  return cond;
+}
+
+
+void LCodeGen::DoIsStringAndBranch(LIsStringAndBranch* instr) {
+  Register reg = ToRegister(instr->InputAt(0));
+  Register temp = ToRegister(instr->TempAt(0));
+
+  int true_block = chunk_->LookupDestination(instr->true_block_id());
+  int false_block = chunk_->LookupDestination(instr->false_block_id());
+  Label* true_label = chunk_->GetAssemblyLabel(true_block);
+  Label* false_label = chunk_->GetAssemblyLabel(false_block);
+
+  Condition true_cond = EmitIsString(reg, temp, false_label, true_label);
+
+  EmitBranch(true_block, false_block, true_cond);
+}
+
+
 void LCodeGen::DoIsSmiAndBranch(LIsSmiAndBranch* instr) {
   Operand input = ToOperand(instr->InputAt(0));
 
@@ -1743,6 +1770,41 @@ void LCodeGen::DoIsUndetectableAndBranch(LIsUndetectableAndBranch* instr) {
 }
 
 
+static Condition ComputeCompareCondition(Token::Value op) {
+  switch (op) {
+    case Token::EQ_STRICT:
+    case Token::EQ:
+      return equal;
+    case Token::LT:
+      return less;
+    case Token::GT:
+      return greater;
+    case Token::LTE:
+      return less_equal;
+    case Token::GTE:
+      return greater_equal;
+    default:
+      UNREACHABLE();
+      return no_condition;
+  }
+}
+
+
+void LCodeGen::DoStringCompareAndBranch(LStringCompareAndBranch* instr) {
+  Token::Value op = instr->op();
+  int true_block = chunk_->LookupDestination(instr->true_block_id());
+  int false_block = chunk_->LookupDestination(instr->false_block_id());
+
+  Handle<Code> ic = CompareIC::GetUninitialized(op);
+  CallCode(ic, RelocInfo::CODE_TARGET, instr);
+
+  Condition condition = ComputeCompareCondition(op);
+  __ test(eax, Operand(eax));
+
+  EmitBranch(true_block, false_block, condition);
+}
+
+
 static InstanceType TestType(HHasInstanceTypeAndBranch* instr) {
   InstanceType from = instr->from();
   InstanceType to = instr->to();
@@ -2016,26 +2078,6 @@ void LCodeGen::DoDeferredLInstanceOfKnownGlobal(LInstanceOfKnownGlobal* instr,
 }
 
 
-static Condition ComputeCompareCondition(Token::Value op) {
-  switch (op) {
-    case Token::EQ_STRICT:
-    case Token::EQ:
-      return equal;
-    case Token::LT:
-      return less;
-    case Token::GT:
-      return greater;
-    case Token::LTE:
-      return less_equal;
-    case Token::GTE:
-      return greater_equal;
-    default:
-      UNREACHABLE();
-      return no_condition;
-  }
-}
-
-
 void LCodeGen::DoCmpT(LCmpT* instr) {
   Token::Value op = instr->op();
 

src/ia32/lithium-codegen-ia32.h

@@ -283,6 +283,14 @@ class LCodeGen BASE_EMBEDDED {
                          Label* is_not_object,
                          Label* is_object);
 
+  // Emits optimized code for %_IsString(x).  Preserves input register.
+  // Returns the condition on which a final split to
+  // true and false label should be made, to optimize fallthrough.
+  Condition EmitIsString(Register input,
+                         Register temp1,
+                         Label* is_not_string,
+                         Label* is_string);
+
   // Emits optimized code for %_IsConstructCall().
   // Caller should branch on equal condition.
   void EmitIsConstructCall(Register temp);

src/ia32/lithium-ia32.cc

@@ -225,6 +225,13 @@ void LIsObjectAndBranch::PrintDataTo(StringStream* stream) {
 }
 
 
+void LIsStringAndBranch::PrintDataTo(StringStream* stream) {
+  stream->Add("if is_string(");
+  InputAt(0)->PrintTo(stream);
+  stream->Add(") then B%d else B%d", true_block_id(), false_block_id());
+}
+
+
 void LIsSmiAndBranch::PrintDataTo(StringStream* stream) {
   stream->Add("if is_smi(");
   InputAt(0)->PrintTo(stream);
@@ -239,6 +246,14 @@ void LIsUndetectableAndBranch::PrintDataTo(StringStream* stream) {
 }
 
 
+void LStringCompareAndBranch::PrintDataTo(StringStream* stream) {
+  stream->Add("if compare_generic(");
+  InputAt(1)->PrintTo(stream);
+  InputAt(2)->PrintTo(stream);
+  stream->Add(") then B%d else B%d", true_block_id(), false_block_id());
+}
+
+
 void LHasInstanceTypeAndBranch::PrintDataTo(StringStream* stream) {
   stream->Add("if has_instance_type(");
   InputAt(0)->PrintTo(stream);
@@ -1498,6 +1513,13 @@ LInstruction* LChunkBuilder::DoIsObjectAndBranch(HIsObjectAndBranch* instr) {
 }
 
 
+LInstruction* LChunkBuilder::DoIsStringAndBranch(HIsStringAndBranch* instr) {
+  ASSERT(instr->value()->representation().IsTagged());
+  LOperand* temp = TempRegister();
+  return new LIsStringAndBranch(UseRegister(instr->value()), temp);
+}
+
+
 LInstruction* LChunkBuilder::DoIsSmiAndBranch(HIsSmiAndBranch* instr) {
   ASSERT(instr->value()->representation().IsTagged());
   return new(zone()) LIsSmiAndBranch(Use(instr->value()));
@@ -1512,6 +1534,21 @@ LInstruction* LChunkBuilder::DoIsUndetectableAndBranch(
 }
 
 
+LInstruction* LChunkBuilder::DoStringCompareAndBranch(
+    HStringCompareAndBranch* instr) {
+  ASSERT(instr->left()->representation().IsTagged());
+  ASSERT(instr->right()->representation().IsTagged());
+  LOperand* context = UseFixed(instr->context(), esi);
+  LOperand* left = UseFixed(instr->left(), edx);
+  LOperand* right = UseFixed(instr->right(), eax);
+
+  LStringCompareAndBranch* result = new
+      LStringCompareAndBranch(context, left, right);
+
+  return MarkAsCall(result, instr);
+}
+
+
 LInstruction* LChunkBuilder::DoHasInstanceTypeAndBranch(
     HHasInstanceTypeAndBranch* instr) {
   ASSERT(instr->value()->representation().IsTagged());

src/ia32/lithium-ia32.h

@@ -103,8 +103,10 @@ class LCodeGen;
   V(IsConstructCallAndBranch)                   \
   V(IsNilAndBranch)                             \
   V(IsObjectAndBranch)                          \
+  V(IsStringAndBranch)                          \
   V(IsSmiAndBranch)                             \
   V(IsUndetectableAndBranch)                    \
+  V(StringCompareAndBranch)                    \
   V(JSArrayLength)                              \
   V(Label)                                      \
   V(LazyBailout)                                \
@@ -643,6 +645,19 @@ class LIsObjectAndBranch: public LControlInstruction<1, 1> {
 };
 
 
+class LIsStringAndBranch: public LControlInstruction<1, 1> {
+ public:
+  LIsStringAndBranch(LOperand* value, LOperand* temp) {
+    inputs_[0] = value;
+    temps_[0] = temp;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(IsStringAndBranch, "is-string-and-branch")
+
+  virtual void PrintDataTo(StringStream* stream);
+};
+
+
 class LIsSmiAndBranch: public LControlInstruction<1, 0> {
  public:
   explicit LIsSmiAndBranch(LOperand* value) {
@@ -670,6 +685,24 @@ class LIsUndetectableAndBranch: public LControlInstruction<1, 1> {
 };
 
 
+class LStringCompareAndBranch: public LControlInstruction<3, 0> {
+ public:
+  LStringCompareAndBranch(LOperand* context, LOperand* left, LOperand* right) {
+    inputs_[0] = context;
+    inputs_[1] = left;
+    inputs_[2] = right;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(StringCompareAndBranch,
+                               "compare-generic-and-branch")
+  DECLARE_HYDROGEN_ACCESSOR(StringCompareAndBranch)
+
+  virtual void PrintDataTo(StringStream* stream);
+
+  Token::Value op() const { return hydrogen()->token(); }
+};
+
+
 class LHasInstanceTypeAndBranch: public LControlInstruction<1, 1> {
  public:
   LHasInstanceTypeAndBranch(LOperand* value, LOperand* temp) {

src/mips/lithium-codegen-mips.cc

@@ -1728,6 +1728,36 @@ void LCodeGen::DoIsObjectAndBranch(LIsObjectAndBranch* instr) {
 }
 
 
+Condition LCodeGen::EmitIsString(Register input,
+                                 Register temp1,
+                                 Label* is_not_string,
+                                 Label* is_string) {
+  __ JumpIfSmi(input, is_not_string);
+  __ GetObjectType(input, temp1, temp1);
+  __ Branch(is_not_string, ge, temp1, Operand(FIRST_NONSTRING_TYPE));
+
+  return lt;
+}
+
+
+void LCodeGen::DoIsStringAndBranch(LIsStringAndBranch* instr) {
+  Register reg = ToRegister(instr->InputAt(0));
+  Register temp1 = ToRegister(instr->TempAt(0));
+  Register temp2 = scratch0();
+
+  int true_block = chunk_->LookupDestination(instr->true_block_id());
+  int false_block = chunk_->LookupDestination(instr->false_block_id());
+  Label* true_label = chunk_->GetAssemblyLabel(true_block);
+  Label* false_label = chunk_->GetAssemblyLabel(false_block);
+
+  Condition true_cond =
+      EmitIsString(reg, temp1, false_label, true_label);
+
+  EmitBranch(true_block, false_block, true_cond, temp2,
+             Operand(LAST_NONCALLABLE_SPEC_OBJECT_TYPE));
+}
+
+
 void LCodeGen::DoIsSmiAndBranch(LIsSmiAndBranch* instr) {
   int true_block = chunk_->LookupDestination(instr->true_block_id());
   int false_block = chunk_->LookupDestination(instr->false_block_id());
@@ -1753,6 +1783,42 @@ void LCodeGen::DoIsUndetectableAndBranch(LIsUndetectableAndBranch* instr) {
 }
 
 
+static Condition ComputeCompareCondition(Token::Value op) {
+  switch (op) {
+    case Token::EQ_STRICT:
+    case Token::EQ:
+      return eq;
+    case Token::LT:
+      return lt;
+    case Token::GT:
+      return gt;
+    case Token::LTE:
+      return le;
+    case Token::GTE:
+      return ge;
+    default:
+      UNREACHABLE();
+      return kNoCondition;
+  }
+}
+
+
+void LCodeGen::DoStringCompareAndBranch(LStringCompareAndBranch* instr) {
+  Token::Value op = instr->op();
+  int true_block = chunk_->LookupDestination(instr->true_block_id());
+  int false_block = chunk_->LookupDestination(instr->false_block_id());
+
+  Handle<Code> ic = CompareIC::GetUninitialized(op);
+  CallCode(ic, RelocInfo::CODE_TARGET, instr);
+  // On MIPS there is no need for a "no inlined smi code" marker (nop).
+
+  Condition condition = ComputeCompareCondition(op);
+
+  EmitBranch(true_block, false_block, condition, at,
+             Operand(LAST_NONCALLABLE_SPEC_OBJECT_TYPE));
+}
+
+
 static InstanceType TestType(HHasInstanceTypeAndBranch* instr) {
   InstanceType from = instr->from();
   InstanceType to = instr->to();
@@ -2050,26 +2116,6 @@ void LCodeGen::DoDeferredLInstanceOfKnownGlobal(LInstanceOfKnownGlobal* instr,
 }
 
 
-static Condition ComputeCompareCondition(Token::Value op) {
-  switch (op) {
-    case Token::EQ_STRICT:
-    case Token::EQ:
-      return eq;
-    case Token::LT:
-      return lt;
-    case Token::GT:
-      return gt;
-    case Token::LTE:
-      return le;
-    case Token::GTE:
-      return ge;
-    default:
-      UNREACHABLE();
-      return kNoCondition;
-  }
-}
-
-
 void LCodeGen::DoCmpT(LCmpT* instr) {
   Token::Value op = instr->op();
 

src/mips/lithium-codegen-mips.h

@@ -303,6 +303,14 @@ class LCodeGen BASE_EMBEDDED {
                          Label* is_not_object,
                          Label* is_object);
 
+  // Emits optimized code for %_IsString(x).  Preserves input register.
+  // Returns the condition on which a final split to
+  // true and false label should be made, to optimize fallthrough.
+  Condition EmitIsString(Register input,
+                         Register temp1,
+                         Label* is_not_object,
+                         Label* is_object);
+
   // Emits optimized code for %_IsConstructCall().
   // Caller should branch on equal condition.
   void EmitIsConstructCall(Register temp1, Register temp2);

src/mips/lithium-mips.cc

@@ -228,6 +228,13 @@ void LIsObjectAndBranch::PrintDataTo(StringStream* stream) {
 }
 
 
+void LIsStringAndBranch::PrintDataTo(StringStream* stream) {
+  stream->Add("if is_string(");
+  InputAt(0)->PrintTo(stream);
+  stream->Add(") then B%d else B%d", true_block_id(), false_block_id());
+}
+
+
 void LIsSmiAndBranch::PrintDataTo(StringStream* stream) {
   stream->Add("if is_smi(");
   InputAt(0)->PrintTo(stream);
@@ -242,6 +249,14 @@ void LIsUndetectableAndBranch::PrintDataTo(StringStream* stream) {
 }
 
 
+void LStringCompareAndBranch::PrintDataTo(StringStream* stream) {
+  stream->Add("if compare_generic(");
+  InputAt(0)->PrintTo(stream);
+  InputAt(1)->PrintTo(stream);
+  stream->Add(") then B%d else B%d", true_block_id(), false_block_id());
+}
+
+
 void LHasInstanceTypeAndBranch::PrintDataTo(StringStream* stream) {
   stream->Add("if has_instance_type(");
   InputAt(0)->PrintTo(stream);
@@ -1400,7 +1415,7 @@ LInstruction* LChunkBuilder::DoCompareGeneric(HCompareGeneric* instr) {
   LOperand* left = UseFixed(instr->left(), a1);
   LOperand* right = UseFixed(instr->right(), a0);
   LCmpT* result = new LCmpT(left, right);
-  return MarkAsCall(DefineFixed(result, v0), instr);
+  return AssignEnvironment(MarkAsCall(DefineFixed(result, v0), instr));
 }
 
 
@@ -1451,6 +1466,13 @@ LInstruction* LChunkBuilder::DoIsObjectAndBranch(HIsObjectAndBranch* instr) {
 }
 
 
+LInstruction* LChunkBuilder::DoIsStringAndBranch(HIsStringAndBranch* instr) {
+  ASSERT(instr->value()->representation().IsTagged());
+  LOperand* temp = TempRegister();
+  return new LIsStringAndBranch(UseRegisterAtStart(instr->value()), temp);
+}
+
+
 LInstruction* LChunkBuilder::DoIsSmiAndBranch(HIsSmiAndBranch* instr) {
   ASSERT(instr->value()->representation().IsTagged());
   return new LIsSmiAndBranch(Use(instr->value()));
@@ -1465,6 +1487,18 @@ LInstruction* LChunkBuilder::DoIsUndetectableAndBranch(
 }
 
 
+LInstruction* LChunkBuilder::DoStringCompareAndBranch(
+    HStringCompareAndBranch* instr) {
+  Representation r = instr->GetInputRepresentation();
+  ASSERT(instr->left()->representation().IsTagged());
+  ASSERT(instr->right()->representation().IsTagged());
+  LOperand* left = UseFixed(instr->left(), a1);
+  LOperand* right = UseFixed(instr->right(), a0);
+  LStringCompareAndBranch* result = new LStringCompareAndBranch(left, right);
+  return MarkAsCall(result, instr);
+}
+
+
 LInstruction* LChunkBuilder::DoHasInstanceTypeAndBranch(
     HHasInstanceTypeAndBranch* instr) {
   ASSERT(instr->value()->representation().IsTagged());

src/mips/lithium-mips.h

@@ -109,8 +109,10 @@ class LCodeGen;
   V(IsConstructCallAndBranch)                   \
   V(IsNilAndBranch)                             \
   V(IsObjectAndBranch)                          \
+  V(IsStringAndBranch)                          \
   V(IsSmiAndBranch)                             \
   V(IsUndetectableAndBranch)                    \
+  V(StringCompareAndBranch)                    \
   V(JSArrayLength)                              \
   V(Label)                                      \
   V(LazyBailout)                                \
@@ -658,6 +660,20 @@ class LIsObjectAndBranch: public LControlInstruction<1, 1> {
 };
 
 
+class LIsStringAndBranch: public LControlInstruction<1, 1> {
+ public:
+  LIsStringAndBranch(LOperand* value, LOperand* temp) {
+    inputs_[0] = value;
+    temps_[0] = temp;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(IsStringAndBranch, "is-string-and-branch")
+  DECLARE_HYDROGEN_ACCESSOR(IsStringAndBranch)
+
+  virtual void PrintDataTo(StringStream* stream);
+};
+
+
 class LIsSmiAndBranch: public LControlInstruction<1, 0> {
  public:
   explicit LIsSmiAndBranch(LOperand* value) {
@@ -686,6 +702,23 @@ class LIsUndetectableAndBranch: public LControlInstruction<1, 1> {
 };
 
 
+class LStringCompareAndBranch: public LControlInstruction<2, 0> {
+ public:
+  LStringCompareAndBranch(LOperand* left, LOperand* right) {
+    inputs_[0] = left;
+    inputs_[1] = right;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(StringCompareAndBranch,
+                               "compare-generic-and-branch")
+  DECLARE_HYDROGEN_ACCESSOR(StringCompareAndBranch)
+
+  Token::Value op() const { return hydrogen()->token(); }
+
+  virtual void PrintDataTo(StringStream* stream);
+};
+
+
 class LHasInstanceTypeAndBranch: public LControlInstruction<1, 0> {
  public:
   explicit LHasInstanceTypeAndBranch(LOperand* value) {

src/type-info.cc

@@ -360,6 +360,10 @@ TypeInfo TypeFeedbackOracle::SwitchType(CaseClause* clause) {
       return unknown;
     case CompareIC::SMIS:
       return TypeInfo::Smi();
+    case CompareIC::STRINGS:
+      return TypeInfo::String();
+    case CompareIC::SYMBOLS:
+      return TypeInfo::Symbol();
     case CompareIC::HEAP_NUMBERS:
       return TypeInfo::Number();
     case CompareIC::OBJECTS:

src/type-info.h

@@ -64,6 +64,8 @@ class TypeInfo {
   static TypeInfo Integer32() { return TypeInfo(kInteger32); }
   // We know it's a Smi.
   static TypeInfo Smi() { return TypeInfo(kSmi); }
+  // We know it's a Symbol.
+  static TypeInfo Symbol() { return TypeInfo(kSymbol); }
   // We know it's a heap number.
   static TypeInfo Double() { return TypeInfo(kDouble); }
   // We know it's a string.
@@ -137,6 +139,16 @@ class TypeInfo {
     return ((type_ & kSmi) == kSmi);
   }
 
+  inline bool IsSymbol() {
+    ASSERT(type_ != kUninitialized);
+    return ((type_ & kSymbol) == kSymbol);
+  }
+
+  inline bool IsNonSymbol() {
+    ASSERT(type_ != kUninitialized);
+    return ((type_ & kSymbol) == kString);
+  }
+
   inline bool IsInteger32() {
     ASSERT(type_ != kUninitialized);
     return ((type_ & kInteger32) == kInteger32);
@@ -168,6 +180,7 @@ class TypeInfo {
       case kNumber: return "Number";
       case kInteger32: return "Integer32";
       case kSmi: return "Smi";
+      case kSymbol: return "Symbol";
       case kDouble: return "Double";
       case kString: return "String";
       case kNonPrimitive: return "Object";
@@ -186,6 +199,7 @@ class TypeInfo {
     kSmi = 0x17,           // 0010111
     kDouble = 0x19,        // 0011001
     kString = 0x30,        // 0110000
+    kSymbol = 0x32,        // 0110010
     kNonPrimitive = 0x40,  // 1000000
     kUninitialized = 0x7f  // 1111111
   };

src/x64/lithium-codegen-x64.cc

@@ -1680,6 +1680,31 @@ void LCodeGen::DoIsObjectAndBranch(LIsObjectAndBranch* instr) {
 }
 
 
+Condition LCodeGen::EmitIsString(Register input,
+                                 Label* is_not_string,
+                                 Label* is_string) {
+
+  __ JumpIfSmi(input, is_not_string);
+  __ CmpObjectType(input, FIRST_NONSTRING_TYPE, rcx);
+
+  return below;
+}
+
+
+void LCodeGen::DoIsStringAndBranch(LIsStringAndBranch* instr) {
+  Register reg = ToRegister(instr->InputAt(0));
+
+  int true_block = chunk_->LookupDestination(instr->true_block_id());
+  int false_block = chunk_->LookupDestination(instr->false_block_id());
+  Label* true_label = chunk_->GetAssemblyLabel(true_block);
+  Label* false_label = chunk_->GetAssemblyLabel(false_block);
+
+  Condition true_cond = EmitIsString(reg, false_label, true_label);
+
+  EmitBranch(true_block, false_block, true_cond);
+}
+
+
 void LCodeGen::DoIsSmiAndBranch(LIsSmiAndBranch* instr) {
   int true_block = chunk_->LookupDestination(instr->true_block_id());
   int false_block = chunk_->LookupDestination(instr->false_block_id());
@@ -1711,6 +1736,21 @@ void LCodeGen::DoIsUndetectableAndBranch(LIsUndetectableAndBranch* instr) {
 }
 
 
+void LCodeGen::DoStringCompareAndBranch(LStringCompareAndBranch* instr) {
+  Token::Value op = instr->op();
+  int true_block = chunk_->LookupDestination(instr->true_block_id());
+  int false_block = chunk_->LookupDestination(instr->false_block_id());
+
+  Handle<Code> ic = CompareIC::GetUninitialized(op);
+  CallCode(ic, RelocInfo::CODE_TARGET, instr);
+
+  Condition condition = TokenToCondition(op, false);
+  __ testq(rax, rax);
+
+  EmitBranch(true_block, false_block, condition);
+}
+
+
 static InstanceType TestType(HHasInstanceTypeAndBranch* instr) {
   InstanceType from = instr->from();
   InstanceType to = instr->to();

src/x64/lithium-codegen-x64.h

@@ -271,6 +271,13 @@ class LCodeGen BASE_EMBEDDED {
                          Label* is_not_object,
                          Label* is_object);
 
+  // Emits optimized code for %_IsString(x).  Preserves input register.
+  // Returns the condition on which a final split to
+  // true and false label should be made, to optimize fallthrough.
+  Condition EmitIsString(Register input,
+                         Label* is_not_object,
+                         Label* is_object);
+
   // Emits optimized code for %_IsConstructCall().
   // Caller should branch on equal condition.
   void EmitIsConstructCall(Register temp);

src/x64/lithium-x64.cc

@@ -230,6 +230,13 @@ void LIsObjectAndBranch::PrintDataTo(StringStream* stream) {
 }
 
 
+void LIsStringAndBranch::PrintDataTo(StringStream* stream) {
+  stream->Add("if is_string(");
+  InputAt(0)->PrintTo(stream);
+  stream->Add(") then B%d else B%d", true_block_id(), false_block_id());
+}
+
+
 void LIsSmiAndBranch::PrintDataTo(StringStream* stream) {
   stream->Add("if is_smi(");
   InputAt(0)->PrintTo(stream);
@@ -244,6 +251,14 @@ void LIsUndetectableAndBranch::PrintDataTo(StringStream* stream) {
 }
 
 
+void LStringCompareAndBranch::PrintDataTo(StringStream* stream) {
+  stream->Add("if compare_generic(");
+  InputAt(0)->PrintTo(stream);
+  InputAt(1)->PrintTo(stream);
+  stream->Add(") then B%d else B%d", true_block_id(), false_block_id());
+}
+
+
 void LHasInstanceTypeAndBranch::PrintDataTo(StringStream* stream) {
   stream->Add("if has_instance_type(");
   InputAt(0)->PrintTo(stream);
@@ -1392,7 +1407,7 @@ LInstruction* LChunkBuilder::DoCompareGeneric(HCompareGeneric* instr) {
   LOperand* left = UseFixed(instr->left(), rdx);
   LOperand* right = UseFixed(instr->right(), rax);
   LCmpT* result = new LCmpT(left, right);
-  return MarkAsCall(DefineFixed(result, rax), instr);
+  return AssignEnvironment(MarkAsCall(DefineFixed(result, rax), instr));
 }
 
 
@@ -1450,6 +1465,12 @@ LInstruction* LChunkBuilder::DoIsObjectAndBranch(HIsObjectAndBranch* instr) {
 }
 
 
+LInstruction* LChunkBuilder::DoIsStringAndBranch(HIsStringAndBranch* instr) {
+  ASSERT(instr->value()->representation().IsTagged());
+  return new LIsStringAndBranch(UseRegisterAtStart(instr->value()));
+}
+
+
 LInstruction* LChunkBuilder::DoIsSmiAndBranch(HIsSmiAndBranch* instr) {
   ASSERT(instr->value()->representation().IsTagged());
   return new LIsSmiAndBranch(Use(instr->value()));
@@ -1464,6 +1485,19 @@ LInstruction* LChunkBuilder::DoIsUndetectableAndBranch(
 }
 
 
+LInstruction* LChunkBuilder::DoStringCompareAndBranch(
+    HStringCompareAndBranch* instr) {
+
+  ASSERT(instr->left()->representation().IsTagged());
+  ASSERT(instr->right()->representation().IsTagged());
+  LOperand* left = UseFixed(instr->left(), rdx);
+  LOperand* right = UseFixed(instr->right(), rax);
+  LStringCompareAndBranch* result = new LStringCompareAndBranch(left, right);
+
+  return MarkAsCall(result, instr);
+}
+
+
 LInstruction* LChunkBuilder::DoHasInstanceTypeAndBranch(
     HHasInstanceTypeAndBranch* instr) {
   ASSERT(instr->value()->representation().IsTagged());

src/x64/lithium-x64.h

@@ -109,8 +109,10 @@ class LCodeGen;
   V(IsConstructCallAndBranch)                   \
   V(IsNilAndBranch)                             \
   V(IsObjectAndBranch)                          \
+  V(IsStringAndBranch)                          \
   V(IsSmiAndBranch)                             \
   V(IsUndetectableAndBranch)                    \
+  V(StringCompareAndBranch)                    \
   V(JSArrayLength)                              \
   V(Label)                                      \
   V(LazyBailout)                                \
@@ -640,6 +642,19 @@ class LIsObjectAndBranch: public LControlInstruction<1, 0> {
 };
 
 
+class LIsStringAndBranch: public LControlInstruction<1, 0> {
+ public:
+  explicit LIsStringAndBranch(LOperand* value) {
+    inputs_[0] = value;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(IsStringAndBranch, "is-string-and-branch")
+  DECLARE_HYDROGEN_ACCESSOR(IsStringAndBranch)
+
+  virtual void PrintDataTo(StringStream* stream);
+};
+
+
 class LIsSmiAndBranch: public LControlInstruction<1, 0> {
  public:
   explicit LIsSmiAndBranch(LOperand* value) {
@@ -668,6 +683,23 @@ class LIsUndetectableAndBranch: public LControlInstruction<1, 1> {
 };
 
 
+class LStringCompareAndBranch: public LControlInstruction<2, 0> {
+ public:
+  explicit LStringCompareAndBranch(LOperand* left, LOperand* right) {
+    inputs_[0] = left;
+    inputs_[1] = right;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(StringCompareAndBranch,
+                               "compare-generic-and-branch")
+  DECLARE_HYDROGEN_ACCESSOR(StringCompareAndBranch)
+
+  virtual void PrintDataTo(StringStream* stream);
+
+  Token::Value op() const { return hydrogen()->token(); }
+};
+
+
 class LHasInstanceTypeAndBranch: public LControlInstruction<1, 0> {
  public:
   explicit LHasInstanceTypeAndBranch(LOperand* value) {

test/mjsunit/switch.js

@@ -126,6 +126,42 @@ assertEquals(3, f4(1), "fallthrough-switch.1");
 assertEquals(3, f4(2), "fallthrough-switch.2");
 assertEquals(5, f4(3), "fallthrough-switch.3");
 
+function f4_string(tag, x) {
+  switch(tag) {
+    case 'zero':
+      x++;
+    case 'two':
+      x++;
+  }
+  return x;
+}
+
+// Symbols
+assertEquals(2, f4_string('zero', 0), "fallthrough-string-switch.0");
+assertEquals(1, f4_string('one', 1), "fallthrough-string-switch.1");
+assertEquals(3, f4_string('two', 2), "fallthrough-string-switch.2");
+
+// Strings
+assertEquals(2, f4_string('_zero'.slice(1), 0), "fallthrough-string-switch.3");
+assertEquals(1, f4_string('_one'.slice(1), 1), "fallthrough-string-switch.4");
+assertEquals(3, f4_string('_two'.slice(1), 2), "fallthrough-string-switch.5");
+
+// Oddball
+assertEquals(3, f4_string(null, 3), "fallthrough-string-switch.6");
+
+// Test for regression
+function regress_string(value) {
+  var json = 1;
+  switch (typeof value) {
+    case 'object':
+      break;
+
+    default:
+
+  }
+  return json;
+};
+assertEquals(1, regress_string('object'), 'regression-string');
 
 function f5(x) {
   switch(x) {