From: yangguo@chromium.org <yangguo@chromium.org@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Wed, 5 Dec 2012 15:49:22 +0000 (+0000)
Subject: Improve array to string conversion.
X-Git-Tag: upstream/4.7.83~15493
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=c75ca450001137a4e63259d455f9540f872390cf;p=platform%2Fupstream%2Fv8.git

Improve array to string conversion.

BUG=v8:2435

Review URL: https://chromiumcodereview.appspot.com/11348349

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13144 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
---

diff --git a/src/arm/codegen-arm.cc b/src/arm/codegen-arm.cc
index a2762f8..5e8739c 100644
--- a/src/arm/codegen-arm.cc
+++ b/src/arm/codegen-arm.cc
@@ -521,6 +521,50 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
 }
 
 
+void SeqStringSetCharGenerator::Generate(MacroAssembler* masm,
+                                         String::Encoding encoding,
+                                         Register string,
+                                         Register index,
+                                         Register value) {
+  if (FLAG_debug_code) {
+    __ tst(index, Operand(kSmiTagMask));
+    __ Check(eq, "Non-smi index");
+    __ tst(value, Operand(kSmiTagMask));
+    __ Check(eq, "Non-smi value");
+
+    __ ldr(ip, FieldMemOperand(string, String::kLengthOffset));
+    __ cmp(index, ip);
+    __ Check(lt, "Index is too large");
+
+    __ cmp(index, Operand(Smi::FromInt(0)));
+    __ Check(ge, "Index is negative");
+
+    __ ldr(ip, FieldMemOperand(string, HeapObject::kMapOffset));
+    __ ldrb(ip, FieldMemOperand(ip, Map::kInstanceTypeOffset));
+
+    __ and_(ip, ip, Operand(kStringRepresentationMask | kStringEncodingMask));
+    static const uint32_t one_byte_seq_type = kSeqStringTag | kOneByteStringTag;
+    static const uint32_t two_byte_seq_type = kSeqStringTag | kTwoByteStringTag;
+    __ cmp(ip, Operand(encoding == String::ONE_BYTE_ENCODING
+                           ? one_byte_seq_type : two_byte_seq_type));
+    __ Check(eq, "Unexpected string type");
+  }
+
+  __ add(ip,
+         string,
+         Operand(SeqString::kHeaderSize - kHeapObjectTag));
+  __ SmiUntag(value, value);
+  STATIC_ASSERT(kSmiTagSize == 1 && kSmiTag == 0);
+  if (encoding == String::ONE_BYTE_ENCODING) {
+    // Smis are tagged by left shift by 1, thus LSR by 1 to smi-untag inline.
+    __ strb(value, MemOperand(ip, index, LSR, 1));
+  } else {
+    // No need to untag a smi for two-byte addressing.
+    __ strh(value, MemOperand(ip, index));
+  }
+}
+
+
 static MemOperand ExpConstant(int index, Register base) {
   return MemOperand(base, index * kDoubleSize);
 }
diff --git a/src/arm/full-codegen-arm.cc b/src/arm/full-codegen-arm.cc
index b0df846..631e101 100644
--- a/src/arm/full-codegen-arm.cc
+++ b/src/arm/full-codegen-arm.cc
@@ -3142,6 +3142,39 @@ void FullCodeGenerator::EmitDateField(CallRuntime* expr) {
 }
 
 
+void FullCodeGenerator::EmitOneByteSeqStringSetChar(CallRuntime* expr) {
+  ZoneList<Expression*>* args = expr->arguments();
+  ASSERT_EQ(3, args->length());
+
+  VisitForStackValue(args->at(1));  // index
+  VisitForStackValue(args->at(2));  // value
+  __ pop(r2);
+  __ pop(r1);
+  VisitForAccumulatorValue(args->at(0));  // string
+
+  static const String::Encoding encoding = String::ONE_BYTE_ENCODING;
+  SeqStringSetCharGenerator::Generate(masm_, encoding, r0, r1, r2);
+  context()->Plug(r0);
+}
+
+
+void FullCodeGenerator::EmitTwoByteSeqStringSetChar(CallRuntime* expr) {
+  ZoneList<Expression*>* args = expr->arguments();
+  ASSERT_EQ(3, args->length());
+
+  VisitForStackValue(args->at(1));  // index
+  VisitForStackValue(args->at(2));  // value
+  __ pop(r2);
+  __ pop(r1);
+  VisitForAccumulatorValue(args->at(0));  // string
+
+  static const String::Encoding encoding = String::TWO_BYTE_ENCODING;
+  SeqStringSetCharGenerator::Generate(masm_, encoding, r0, r1, r2);
+  context()->Plug(r0);
+}
+
+
+
 void FullCodeGenerator::EmitMathPow(CallRuntime* expr) {
   // Load the arguments on the stack and call the runtime function.
   ZoneList<Expression*>* args = expr->arguments();
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index 400e1fc..921489e 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -1647,6 +1647,16 @@ LInstruction* LChunkBuilder::DoDateField(HDateField* instr) {
 }
 
 
+LInstruction* LChunkBuilder::DoSeqStringSetChar(HSeqStringSetChar* instr) {
+  LOperand* string = UseRegister(instr->string());
+  LOperand* index = UseRegister(instr->index());
+  LOperand* value = UseRegister(instr->value());
+  LSeqStringSetChar* result =
+      new(zone()) LSeqStringSetChar(instr->encoding(), string, index, value);
+  return DefineAsRegister(result);
+}
+
+
 LInstruction* LChunkBuilder::DoBoundsCheck(HBoundsCheck* instr) {
   LOperand* value = UseRegisterOrConstantAtStart(instr->index());
   LOperand* length = UseRegister(instr->length());
diff --git a/src/arm/lithium-arm.h b/src/arm/lithium-arm.h
index 3a9d10b..1b589ce 100644
--- a/src/arm/lithium-arm.h
+++ b/src/arm/lithium-arm.h
@@ -150,6 +150,7 @@ class LCodeGen;
   V(Random)                                     \
   V(RegExpLiteral)                              \
   V(Return)                                     \
+  V(SeqStringSetChar)                           \
   V(ShiftI)                                     \
   V(SmiTag)                                     \
   V(SmiUntag)                                   \
@@ -1203,6 +1204,30 @@ class LDateField: public LTemplateInstruction<1, 1, 1> {
 };
 
 
+class LSeqStringSetChar: public LTemplateInstruction<1, 3, 0> {
+ public:
+  LSeqStringSetChar(String::Encoding encoding,
+                    LOperand* string,
+                    LOperand* index,
+                    LOperand* value) : encoding_(encoding) {
+    inputs_[0] = string;
+    inputs_[1] = index;
+    inputs_[2] = value;
+  }
+
+  String::Encoding encoding() { return encoding_; }
+  LOperand* string() { return inputs_[0]; }
+  LOperand* index() { return inputs_[1]; }
+  LOperand* value() { return inputs_[2]; }
+
+  DECLARE_CONCRETE_INSTRUCTION(SeqStringSetChar, "seq-string-set-char")
+  DECLARE_HYDROGEN_ACCESSOR(SeqStringSetChar)
+
+ private:
+  String::Encoding encoding_;
+};
+
+
 class LThrow: public LTemplateInstruction<0, 1, 0> {
  public:
   explicit LThrow(LOperand* value) {
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 1c9d0c4..1cfa8e9 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -1845,6 +1845,15 @@ void LCodeGen::DoDateField(LDateField* instr) {
 }
 
 
+void LCodeGen::DoSeqStringSetChar(LSeqStringSetChar* instr) {
+  SeqStringSetCharGenerator::Generate(masm(),
+                                      instr->encoding(),
+                                      ToRegister(instr->string()),
+                                      ToRegister(instr->index()),
+                                      ToRegister(instr->value()));
+}
+
+
 void LCodeGen::DoBitNotI(LBitNotI* instr) {
   Register input = ToRegister(instr->value());
   Register result = ToRegister(instr->result());
diff --git a/src/codegen.h b/src/codegen.h
index 3d14502..0ac68c2 100644
--- a/src/codegen.h
+++ b/src/codegen.h
@@ -104,6 +104,19 @@ class ElementsTransitionGenerator : public AllStatic {
   DISALLOW_COPY_AND_ASSIGN(ElementsTransitionGenerator);
 };
 
+
+class SeqStringSetCharGenerator : public AllStatic {
+ public:
+  static void Generate(MacroAssembler* masm,
+                       String::Encoding encoding,
+                       Register string,
+                       Register index,
+                       Register value);
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SeqStringSetCharGenerator);
+};
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_CODEGEN_H_
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 47a9da3..3006734 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -155,6 +155,7 @@ class LChunkBuilder;
   V(Return)                                    \
   V(Ror)                                       \
   V(Sar)                                       \
+  V(SeqStringSetChar)                          \
   V(Shl)                                       \
   V(Shr)                                       \
   V(Simulate)                                  \
@@ -5212,6 +5213,33 @@ class HDateField: public HUnaryOperation {
 };
 
 
+class HSeqStringSetChar: public HTemplateInstruction<3> {
+ public:
+  HSeqStringSetChar(String::Encoding encoding,
+                    HValue* string,
+                    HValue* index,
+                    HValue* value) : encoding_(encoding) {
+    SetOperandAt(0, string);
+    SetOperandAt(1, index);
+    SetOperandAt(2, value);
+  }
+
+  String::Encoding encoding() { return encoding_; }
+  HValue* string() { return OperandAt(0); }
+  HValue* index() { return OperandAt(1); }
+  HValue* value() { return OperandAt(2); }
+
+  virtual Representation RequiredInputRepresentation(int index) {
+    return Representation::Tagged();
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(SeqStringSetChar)
+
+ private:
+  String::Encoding encoding_;
+};
+
+
 class HDeleteProperty: public HBinaryOperation {
  public:
   HDeleteProperty(HValue* context, HValue* obj, HValue* key)
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 4fd14e8..6291dcb 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -9180,6 +9180,39 @@ void HOptimizedGraphBuilder::GenerateDateField(CallRuntime* call) {
 }
 
 
+void HOptimizedGraphBuilder::GenerateOneByteSeqStringSetChar(
+    CallRuntime* call) {
+  ASSERT(call->arguments()->length() == 3);
+  CHECK_ALIVE(VisitForValue(call->arguments()->at(0)));
+  CHECK_ALIVE(VisitForValue(call->arguments()->at(1)));
+  CHECK_ALIVE(VisitForValue(call->arguments()->at(2)));
+  HValue* value = Pop();
+  HValue* index = Pop();
+  HValue* string = Pop();
+  HSeqStringSetChar* result = new(zone()) HSeqStringSetChar(
+      String::ONE_BYTE_ENCODING, string, index, value);
+  return ast_context()->ReturnInstruction(result, call->id());
+}
+
+
+void HOptimizedGraphBuilder::GenerateTwoByteSeqStringSetChar(
+    CallRuntime* call) {
+  ASSERT(call->arguments()->length() == 3);
+  CHECK_ALIVE(VisitForValue(call->arguments()->at(0)));
+  CHECK_ALIVE(VisitForValue(call->arguments()->at(1)));
+  CHECK_ALIVE(VisitForValue(call->arguments()->at(2)));
+  HValue* value = Pop();
+  HValue* index = Pop();
+  HValue* string = Pop();
+  HValue* context = environment()->LookupContext();
+  HStringCharCodeAt* char_code = BuildStringCharCodeAt(context, string, index);
+  AddInstruction(char_code);
+  HSeqStringSetChar* result = new(zone()) HSeqStringSetChar(
+      String::TWO_BYTE_ENCODING, string, index, value);
+  return ast_context()->ReturnInstruction(result, call->id());
+}
+
+
 void HOptimizedGraphBuilder::GenerateSetValueOf(CallRuntime* call) {
   ASSERT(call->arguments()->length() == 2);
   CHECK_ALIVE(VisitForValue(call->arguments()->at(0)));
diff --git a/src/ia32/codegen-ia32.cc b/src/ia32/codegen-ia32.cc
index 2f5553c..9477bf1 100644
--- a/src/ia32/codegen-ia32.cc
+++ b/src/ia32/codegen-ia32.cc
@@ -793,6 +793,50 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
 }
 
 
+void SeqStringSetCharGenerator::Generate(MacroAssembler* masm,
+                                         String::Encoding encoding,
+                                         Register string,
+                                         Register index,
+                                         Register value) {
+  if (FLAG_debug_code) {
+    __ test(index, Immediate(kSmiTagMask));
+    __ Check(zero, "Non-smi index");
+    __ test(value, Immediate(kSmiTagMask));
+    __ Check(zero, "Non-smi value");
+
+    __ cmp(index, FieldOperand(string, String::kLengthOffset));
+    __ Check(less, "Index is too large");
+
+    __ cmp(index, Immediate(Smi::FromInt(0)));
+    __ Check(greater_equal, "Index is negative");
+
+    __ push(value);
+    __ mov(value, FieldOperand(string, HeapObject::kMapOffset));
+    __ movzx_b(value, FieldOperand(value, Map::kInstanceTypeOffset));
+
+    __ and_(value, Immediate(kStringRepresentationMask | kStringEncodingMask));
+    static const uint32_t one_byte_seq_type = kSeqStringTag | kOneByteStringTag;
+    static const uint32_t two_byte_seq_type = kSeqStringTag | kTwoByteStringTag;
+    __ cmp(value, Immediate(encoding == String::ONE_BYTE_ENCODING
+                                ? one_byte_seq_type : two_byte_seq_type));
+    __ Check(equal, "Unexpected string type");
+    __ pop(value);
+  }
+
+  __ SmiUntag(value);
+  STATIC_ASSERT(kSmiTagSize == 1 && kSmiTag == 0);
+  if (encoding == String::ONE_BYTE_ENCODING) {
+    __ SmiUntag(index);
+    __ mov_b(FieldOperand(string, index, times_1, SeqString::kHeaderSize),
+             value);
+  } else {
+    // No need to untag a smi for two-byte addressing.
+    __ mov_w(FieldOperand(string, index, times_1, SeqString::kHeaderSize),
+             value);
+  }
+}
+
+
 static Operand ExpConstant(int index) {
   return Operand::StaticVariable(ExternalReference::math_exp_constants(index));
 }
diff --git a/src/ia32/full-codegen-ia32.cc b/src/ia32/full-codegen-ia32.cc
index 6dfec92..fdafe39 100644
--- a/src/ia32/full-codegen-ia32.cc
+++ b/src/ia32/full-codegen-ia32.cc
@@ -3074,6 +3074,38 @@ void FullCodeGenerator::EmitDateField(CallRuntime* expr) {
 }
 
 
+void FullCodeGenerator::EmitOneByteSeqStringSetChar(CallRuntime* expr) {
+  ZoneList<Expression*>* args = expr->arguments();
+  ASSERT_EQ(3, args->length());
+
+  VisitForStackValue(args->at(1));  // index
+  VisitForStackValue(args->at(2));  // value
+  __ pop(ecx);
+  __ pop(ebx);
+  VisitForAccumulatorValue(args->at(0));  // string
+
+  static const String::Encoding encoding = String::ONE_BYTE_ENCODING;
+  SeqStringSetCharGenerator::Generate(masm_, encoding, eax, ebx, ecx);
+  context()->Plug(eax);
+}
+
+
+void FullCodeGenerator::EmitTwoByteSeqStringSetChar(CallRuntime* expr) {
+  ZoneList<Expression*>* args = expr->arguments();
+  ASSERT_EQ(3, args->length());
+
+  VisitForStackValue(args->at(1));  // index
+  VisitForStackValue(args->at(2));  // value
+  __ pop(ecx);
+  __ pop(ebx);
+  VisitForAccumulatorValue(args->at(0));  // string
+
+  static const String::Encoding encoding = String::TWO_BYTE_ENCODING;
+  SeqStringSetCharGenerator::Generate(masm_, encoding, eax, ebx, ecx);
+  context()->Plug(eax);
+}
+
+
 void FullCodeGenerator::EmitMathPow(CallRuntime* expr) {
   // Load the arguments on the stack and call the runtime function.
   ZoneList<Expression*>* args = expr->arguments();
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index f83c761..ff1ec90 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -1709,6 +1709,15 @@ void LCodeGen::DoDateField(LDateField* instr) {
 }
 
 
+void LCodeGen::DoSeqStringSetChar(LSeqStringSetChar* instr) {
+  SeqStringSetCharGenerator::Generate(masm(),
+                                      instr->encoding(),
+                                      ToRegister(instr->string()),
+                                      ToRegister(instr->index()),
+                                      ToRegister(instr->value()));
+}
+
+
 void LCodeGen::DoBitNotI(LBitNotI* instr) {
   LOperand* input = instr->value();
   ASSERT(input->Equals(instr->result()));
diff --git a/src/ia32/lithium-ia32.cc b/src/ia32/lithium-ia32.cc
index 098e6ff..63afef6 100644
--- a/src/ia32/lithium-ia32.cc
+++ b/src/ia32/lithium-ia32.cc
@@ -1660,6 +1660,17 @@ LInstruction* LChunkBuilder::DoDateField(HDateField* instr) {
 }
 
 
+LInstruction* LChunkBuilder::DoSeqStringSetChar(HSeqStringSetChar* instr) {
+  LOperand* string = UseRegister(instr->string());
+  LOperand* index = UseRegister(instr->index());
+  ASSERT(ecx.is_byte_register());
+  LOperand* value = UseFixed(instr->value(), ecx);
+  LSeqStringSetChar* result =
+      new(zone()) LSeqStringSetChar(instr->encoding(), string, index, value);
+  return DefineSameAsFirst(result);
+}
+
+
 LInstruction* LChunkBuilder::DoBoundsCheck(HBoundsCheck* instr) {
   return AssignEnvironment(new(zone()) LBoundsCheck(
       UseRegisterOrConstantAtStart(instr->index()),
diff --git a/src/ia32/lithium-ia32.h b/src/ia32/lithium-ia32.h
index bec2f81..f4056c1 100644
--- a/src/ia32/lithium-ia32.h
+++ b/src/ia32/lithium-ia32.h
@@ -144,6 +144,7 @@ class LCodeGen;
   V(PushArgument)                               \
   V(RegExpLiteral)                              \
   V(Return)                                     \
+  V(SeqStringSetChar)                           \
   V(ShiftI)                                     \
   V(SmiTag)                                     \
   V(SmiUntag)                                   \
@@ -1184,6 +1185,30 @@ class LDateField: public LTemplateInstruction<1, 1, 1> {
 };
 
 
+class LSeqStringSetChar: public LTemplateInstruction<1, 3, 0> {
+ public:
+  LSeqStringSetChar(String::Encoding encoding,
+                    LOperand* string,
+                    LOperand* index,
+                    LOperand* value) : encoding_(encoding) {
+    inputs_[0] = string;
+    inputs_[1] = index;
+    inputs_[2] = value;
+  }
+
+  String::Encoding encoding() { return encoding_; }
+  LOperand* string() { return inputs_[0]; }
+  LOperand* index() { return inputs_[1]; }
+  LOperand* value() { return inputs_[2]; }
+
+  DECLARE_CONCRETE_INSTRUCTION(SeqStringSetChar, "seq-string-set-char")
+  DECLARE_HYDROGEN_ACCESSOR(SeqStringSetChar)
+
+ private:
+  String::Encoding encoding_;
+};
+
+
 class LThrow: public LTemplateInstruction<0, 2, 0> {
  public:
   LThrow(LOperand* context, LOperand* value) {
diff --git a/src/json-stringifier.h b/src/json-stringifier.h
index 09014f0..7a8af30 100644
--- a/src/json-stringifier.h
+++ b/src/json-stringifier.h
@@ -597,31 +597,8 @@ BasicJsonStringifier::Result BasicJsonStringifier::SerializeJSObject(
 
 void BasicJsonStringifier::ShrinkCurrentPart() {
   ASSERT(current_index_ < part_length_);
-  if (current_index_ == 0) {
-    current_part_ = factory_->empty_string();
-    return;
-  }
-
-  int string_size, allocated_string_size;
-  if (is_ascii_) {
-    allocated_string_size = SeqOneByteString::SizeFor(part_length_);
-    string_size = SeqOneByteString::SizeFor(current_index_);
-  } else {
-    allocated_string_size = SeqTwoByteString::SizeFor(part_length_);
-    string_size = SeqTwoByteString::SizeFor(current_index_);
-  }
-
-  int delta = allocated_string_size - string_size;
-  current_part_->set_length(current_index_);
-
-  // String sizes are pointer size aligned, so that we can use filler objects
-  // that are a multiple of pointer size.
-  Address end_of_string = current_part_->address() + string_size;
-  isolate_->heap()->CreateFillerObjectAt(end_of_string, delta);
-  if (Marking::IsBlack(Marking::MarkBitFrom(*current_part_))) {
-    MemoryChunk::IncrementLiveBytesFromMutator(
-        current_part_->address(), -delta);
-  }
+  current_part_ = Handle<String>(
+      SeqString::cast(*current_part_)->Truncate(current_index_), isolate_);
 }
 
 
diff --git a/src/macros.py b/src/macros.py
index 08fa82e..f871fc5 100644
--- a/src/macros.py
+++ b/src/macros.py
@@ -32,6 +32,8 @@ const NONE        = 0;
 const READ_ONLY   = 1;
 const DONT_ENUM   = 2;
 const DONT_DELETE = 4;
+const NEW_ONE_BYTE_STRING = true;
+const NEW_TWO_BYTE_STRING = false;
 
 # Constants used for getter and setter operations.
 const GETTER = 0;
diff --git a/src/objects.cc b/src/objects.cc
index 2ef142b..a9b58ab 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -7620,6 +7620,36 @@ bool String::SlowAsArrayIndex(uint32_t* index) {
 }
 
 
+String* SeqString::Truncate(int new_length) {
+  Heap* heap = GetHeap();
+  if (new_length <= 0) return heap->empty_string();
+
+  int string_size, allocated_string_size;
+  int old_length = length();
+  if (old_length <= new_length) return this;
+
+  if (IsSeqOneByteString()) {
+    allocated_string_size = SeqOneByteString::SizeFor(old_length);
+    string_size = SeqOneByteString::SizeFor(new_length);
+  } else {
+    allocated_string_size = SeqTwoByteString::SizeFor(old_length);
+    string_size = SeqTwoByteString::SizeFor(new_length);
+  }
+
+  int delta = allocated_string_size - string_size;
+  set_length(new_length);
+
+  // String sizes are pointer size aligned, so that we can use filler objects
+  // that are a multiple of pointer size.
+  Address end_of_string = address() + string_size;
+  heap->CreateFillerObjectAt(end_of_string, delta);
+  if (Marking::IsBlack(Marking::MarkBitFrom(this))) {
+    MemoryChunk::IncrementLiveBytesFromMutator(address(), -delta);
+  }
+  return this;
+}
+
+
 uint32_t StringHasher::MakeArrayIndexHash(uint32_t value, int length) {
   // For array indexes mix the length into the hash as an array index could
   // be zero.
diff --git a/src/objects.h b/src/objects.h
index eace7b7..7d25e9c 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -7173,6 +7173,8 @@ class StringShape BASE_EMBEDDED {
 // All string values have a length field.
 class String: public HeapObject {
  public:
+  enum Encoding { ONE_BYTE_ENCODING, TWO_BYTE_ENCODING };
+
   // Representation of the flat content of a String.
   // A non-flat string doesn't have flat content.
   // A flat string has content that's encoded as a sequence of either
@@ -7569,6 +7571,11 @@ class SeqString: public String {
   // Layout description.
   static const int kHeaderSize = String::kSize;
 
+  // Truncate the string in-place if possible and return the result.
+  // In case of new_length == 0, the empty string is returned without
+  // truncating the original string.
+  MUST_USE_RESULT String* Truncate(int new_length);
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(SeqString);
 };
diff --git a/src/runtime.cc b/src/runtime.cc
index e78086d..9f5e78d 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -5101,46 +5101,22 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_StringToNumber) {
 }
 
 
-RUNTIME_FUNCTION(MaybeObject*, Runtime_StringFromCharCodeArray) {
-  NoHandleAllocation ha;
-  ASSERT(args.length() == 1);
-
-  CONVERT_ARG_CHECKED(JSArray, codes, 0);
-  int length = Smi::cast(codes->length())->value();
-
-  // Check if the string can be ASCII.
-  int i;
-  for (i = 0; i < length; i++) {
-    Object* element;
-    { MaybeObject* maybe_element = codes->GetElement(i);
-      // We probably can't get an exception here, but just in order to enforce
-      // the checking of inputs in the runtime calls we check here.
-      if (!maybe_element->ToObject(&element)) return maybe_element;
-    }
-    CONVERT_NUMBER_CHECKED(int, chr, Int32, element);
-    if ((chr & 0xffff) > String::kMaxAsciiCharCode)
-      break;
+RUNTIME_FUNCTION(MaybeObject*, Runtime_NewString) {
+  CONVERT_SMI_ARG_CHECKED(length, 0);
+  CONVERT_BOOLEAN_ARG_CHECKED(is_one_byte, 1);
+  if (length == 0) return isolate->heap()->empty_string();
+  if (is_one_byte) {
+    return isolate->heap()->AllocateRawOneByteString(length);
+  } else {
+    return isolate->heap()->AllocateRawTwoByteString(length);
   }
+}
 
-  MaybeObject* maybe_object = NULL;
-  if (i == length) {  // The string is ASCII.
-    maybe_object = isolate->heap()->AllocateRawOneByteString(length);
-  } else {  // The string is not ASCII.
-    maybe_object = isolate->heap()->AllocateRawTwoByteString(length);
-  }
 
-  Object* object = NULL;
-  if (!maybe_object->ToObject(&object)) return maybe_object;
-  String* result = String::cast(object);
-  for (int i = 0; i < length; i++) {
-    Object* element;
-    { MaybeObject* maybe_element = codes->GetElement(i);
-      if (!maybe_element->ToObject(&element)) return maybe_element;
-    }
-    CONVERT_NUMBER_CHECKED(int, chr, Int32, element);
-    result->Set(i, chr & 0xffff);
-  }
-  return result;
+RUNTIME_FUNCTION(MaybeObject*, Runtime_TruncateString) {
+  CONVERT_ARG_CHECKED(SeqString, string, 0);
+  CONVERT_SMI_ARG_CHECKED(new_length, 1);
+  return string->Truncate(new_length);
 }
 
 
diff --git a/src/runtime.h b/src/runtime.h
index a52dfb8..7a21bb9 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -114,7 +114,6 @@ namespace internal {
   F(Typeof, 1, 1) \
   \
   F(StringToNumber, 1, 1) \
-  F(StringFromCharCodeArray, 1, 1) \
   F(StringParseInt, 2, 1) \
   F(StringParseFloat, 1, 1) \
   F(StringToLowerCase, 1, 1) \
@@ -123,10 +122,6 @@ namespace internal {
   F(CharFromCode, 1, 1) \
   F(URIEscape, 1, 1) \
   F(URIUnescape, 1, 1) \
-  F(BasicJSONStringify, 1, 1) \
-  F(QuoteJSONString, 1, 1) \
-  F(QuoteJSONStringComma, 1, 1) \
-  F(QuoteJSONStringArray, 1, 1) \
   \
   F(NumberToString, 1, 1) \
   F(NumberToStringSkipCache, 1, 1) \
@@ -195,6 +190,10 @@ namespace internal {
   \
   /* JSON */ \
   F(ParseJson, 1, 1) \
+  F(BasicJSONStringify, 1, 1) \
+  F(QuoteJSONString, 1, 1) \
+  F(QuoteJSONStringComma, 1, 1) \
+  F(QuoteJSONStringArray, 1, 1) \
   \
   /* Strings */ \
   F(StringCharCodeAt, 2, 1) \
@@ -208,6 +207,8 @@ namespace internal {
   F(StringTrim, 3, 1) \
   F(StringToArray, 2, 1) \
   F(NewStringWrapper, 1, 1) \
+  F(NewString, 2, 1) \
+  F(TruncateString, 2, 1) \
   \
   /* Numbers */ \
   F(NumberToRadixString, 2, 1) \
@@ -530,6 +531,8 @@ namespace internal {
   F(DateField, 2 /* date object, field index */, 1)                          \
   F(StringCharFromCode, 1, 1)                                                \
   F(StringCharAt, 2, 1)                                                      \
+  F(OneByteSeqStringSetChar, 3, 1)                                           \
+  F(TwoByteSeqStringSetChar, 3, 1)                                           \
   F(ObjectEquals, 2, 1)                                                      \
   F(RandomHeapNumber, 0, 1)                                                  \
   F(IsObject, 1, 1)                                                          \
diff --git a/src/string.js b/src/string.js
index 1f38194..badfad3 100644
--- a/src/string.js
+++ b/src/string.js
@@ -810,6 +810,7 @@ function StringTrimRight() {
 
 var static_charcode_array = new InternalArray(4);
 
+
 // ECMA-262, section 15.5.3.2
 function StringFromCharCode(code) {
   var n = %_ArgumentsLength();
@@ -818,17 +819,24 @@ function StringFromCharCode(code) {
     return %_StringCharFromCode(code & 0xffff);
   }
 
-  // NOTE: This is not super-efficient, but it is necessary because we
-  // want to avoid converting to numbers from within the virtual
-  // machine. Maybe we can find another way of doing this?
-  var codes = static_charcode_array;
-  for (var i = 0; i < n; i++) {
+  var one_byte = %NewString(n, NEW_ONE_BYTE_STRING);
+  var i;
+  for (i = 0; i < n; i++) {
     var code = %_Arguments(i);
-    if (!%_IsSmi(code)) code = ToNumber(code);
-    codes[i] = code;
+    if (!%_IsSmi(code)) code = ToNumber(code) & 0xffff;
+    if (code > 0x7f) break;
+    %_OneByteSeqStringSetChar(one_byte, i, code);
+  }
+  if (i == n) return one_byte;
+  one_byte = %TruncateString(one_byte, i);
+
+  var two_byte = %NewString(n - i, NEW_TWO_BYTE_STRING);
+  for (var j = 0; i < n; i++, j++) {
+    var code = %_Arguments(i);
+    if (!%_IsSmi(code)) code = ToNumber(code) & 0xffff;
+    %_TwoByteSeqStringSetChar(two_byte, j, code);
   }
-  codes.length = n;
-  return %StringFromCharCodeArray(codes);
+  return one_byte + two_byte;
 }
 
 
diff --git a/src/uri.js b/src/uri.js
index b195f3d..1de22f8 100644
--- a/src/uri.js
+++ b/src/uri.js
@@ -165,11 +165,11 @@ function URIDecodeOctets(octets, result, index) {
     throw new $URIError("URI malformed");
   }
   if (value < 0x10000) {
-    result[index++] = value;
+    %_TwoByteSeqStringSetChar(result, index++, value);
     return index;
   } else {
-    result[index++] = (value >> 10) + 0xd7c0;
-    result[index++] = (value & 0x3ff) + 0xdc00;
+    %_TwoByteSeqStringSetChar(result, index++, (value >> 10) + 0xd7c0);
+    %_TwoByteSeqStringSetChar(result, index++, (value & 0x3ff) + 0xdc00);
     return index;
   }
 }
@@ -178,43 +178,72 @@ function URIDecodeOctets(octets, result, index) {
 // ECMA-262, section 15.1.3
 function Encode(uri, unescape) {
   var uriLength = uri.length;
-  // We are going to pass result to %StringFromCharCodeArray
-  // which does not expect any getters/setters installed
-  // on the incoming array.
-  var result = new InternalArray(uriLength);
+  var array = new InternalArray(uriLength);
   var index = 0;
   for (var k = 0; k < uriLength; k++) {
     var cc1 = uri.charCodeAt(k);
     if (unescape(cc1)) {
-      result[index++] = cc1;
+      array[index++] = cc1;
     } else {
       if (cc1 >= 0xDC00 && cc1 <= 0xDFFF) throw new $URIError("URI malformed");
       if (cc1 < 0xD800 || cc1 > 0xDBFF) {
-        index = URIEncodeSingle(cc1, result, index);
+        index = URIEncodeSingle(cc1, array, index);
       } else {
         k++;
         if (k == uriLength) throw new $URIError("URI malformed");
         var cc2 = uri.charCodeAt(k);
         if (cc2 < 0xDC00 || cc2 > 0xDFFF) throw new $URIError("URI malformed");
-        index = URIEncodePair(cc1, cc2, result, index);
+        index = URIEncodePair(cc1, cc2, array, index);
       }
     }
   }
-  return %StringFromCharCodeArray(result);
+
+  var result = %NewString(array.length, NEW_ONE_BYTE_STRING);
+  for (var i = 0; i < array.length; i++) {
+    %_OneByteSeqStringSetChar(result, i, array[i]);
+  }
+  return result;
 }
 
 
 // ECMA-262, section 15.1.3
 function Decode(uri, reserved) {
   var uriLength = uri.length;
-  // We are going to pass result to %StringFromCharCodeArray
-  // which does not expect any getters/setters installed
-  // on the incoming array.
-  var result = new InternalArray(uriLength);
+  var one_byte = %NewString(uriLength, NEW_ONE_BYTE_STRING);
   var index = 0;
-  for (var k = 0; k < uriLength; k++) {
-    var ch = uri.charAt(k);
-    if (ch == '%') {
+  var k = 0;
+
+  // Optimistically assume ascii string.
+  for ( ; k < uriLength; k++) {
+    var code = uri.charCodeAt(k);
+    if (code == 37) {  // '%'
+      if (k + 2 >= uriLength) throw new $URIError("URI malformed");
+      var cc = URIHexCharsToCharCode(uri.charCodeAt(k+1), uri.charCodeAt(k+2));
+      if (cc >> 7) break;  // Assumption wrong, two byte string.
+      if (reserved(cc)) {
+        %_OneByteSeqStringSetChar(one_byte, index++, 37);  // '%'.
+        %_OneByteSeqStringSetChar(one_byte, index++, uri.charCodeAt(k+1));
+        %_OneByteSeqStringSetChar(one_byte, index++, uri.charCodeAt(k+2));
+      } else {
+        %_OneByteSeqStringSetChar(one_byte, index++, cc);
+      }
+      k += 2;
+    } else {
+      if (code > 0x7f) break;  // Assumption wrong, two byte string.
+      %_OneByteSeqStringSetChar(one_byte, index++, code);
+    }
+  }
+
+  one_byte = %TruncateString(one_byte, index);
+  if (k == uriLength) return one_byte;
+
+  // Write into two byte string.
+  var two_byte = %NewString(uriLength - k, NEW_TWO_BYTE_STRING);
+  index = 0;
+
+  for ( ; k < uriLength; k++) {
+    var code = uri.charCodeAt(k);
+    if (code == 37) {  // '%'
       if (k + 2 >= uriLength) throw new $URIError("URI malformed");
       var cc = URIHexCharsToCharCode(uri.charCodeAt(++k), uri.charCodeAt(++k));
       if (cc >> 7) {
@@ -229,22 +258,21 @@ function Decode(uri, reserved) {
           octets[i] = URIHexCharsToCharCode(uri.charCodeAt(++k),
                                             uri.charCodeAt(++k));
         }
-        index = URIDecodeOctets(octets, result, index);
+        index = URIDecodeOctets(octets, two_byte, index);
+      } else  if (reserved(cc)) {
+        %_TwoByteSeqStringSetChar(two_byte, index++, 37);  // '%'.
+        %_TwoByteSeqStringSetChar(two_byte, index++, uri.charCodeAt(k - 1));
+        %_TwoByteSeqStringSetChar(two_byte, index++, uri.charCodeAt(k));
       } else {
-        if (reserved(cc)) {
-          result[index++] = 37; // Char code of '%'.
-          result[index++] = uri.charCodeAt(k - 1);
-          result[index++] = uri.charCodeAt(k);
-        } else {
-          result[index++] = cc;
-        }
+        %_TwoByteSeqStringSetChar(two_byte, index++, cc);
       }
     } else {
-      result[index++] = ch.charCodeAt(0);
+      %_TwoByteSeqStringSetChar(two_byte, index++, code);
     }
   }
-  result.length = index;
-  return %StringFromCharCodeArray(result);
+
+  two_byte = %TruncateString(two_byte, index);
+  return one_byte + two_byte;
 }
 
 
diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc
index 67d1d90..7954604 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -606,6 +606,46 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
 }
 
 
+void SeqStringSetCharGenerator::Generate(MacroAssembler* masm,
+                                         String::Encoding encoding,
+                                         Register string,
+                                         Register index,
+                                         Register value) {
+  if (FLAG_debug_code) {
+    __ Check(masm->CheckSmi(index), "Non-smi index");
+    __ Check(masm->CheckSmi(value), "Non-smi value");
+
+    __ SmiCompare(index, FieldOperand(string, String::kLengthOffset));
+    __ Check(less, "Index is too large");
+
+    __ SmiCompare(index, Smi::FromInt(0));
+    __ Check(greater_equal, "Index is negative");
+
+    __ push(value);
+    __ movq(value, FieldOperand(string, HeapObject::kMapOffset));
+    __ movzxbq(value, FieldOperand(value, Map::kInstanceTypeOffset));
+
+    __ andb(value, Immediate(kStringRepresentationMask | kStringEncodingMask));
+    static const uint32_t one_byte_seq_type = kSeqStringTag | kOneByteStringTag;
+    static const uint32_t two_byte_seq_type = kSeqStringTag | kTwoByteStringTag;
+    __ cmpq(value, Immediate(encoding == String::ONE_BYTE_ENCODING
+                                 ? one_byte_seq_type : two_byte_seq_type));
+    __ Check(equal, "Unexpected string type");
+    __ pop(value);
+  }
+
+  __ SmiToInteger32(value, value);
+  __ SmiToInteger32(index, index);
+  if (encoding == String::ONE_BYTE_ENCODING) {
+    __ movb(FieldOperand(string, index, times_1, SeqString::kHeaderSize),
+            value);
+  } else {
+    __ movw(FieldOperand(string, index, times_2, SeqString::kHeaderSize),
+            value);
+  }
+}
+
+
 void MathExpGenerator::EmitMathExp(MacroAssembler* masm,
                                    XMMRegister input,
                                    XMMRegister result,
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 650337a..c87155f 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -3047,6 +3047,38 @@ void FullCodeGenerator::EmitDateField(CallRuntime* expr) {
 }
 
 
+void FullCodeGenerator::EmitOneByteSeqStringSetChar(CallRuntime* expr) {
+  ZoneList<Expression*>* args = expr->arguments();
+  ASSERT_EQ(3, args->length());
+
+  VisitForStackValue(args->at(1));  // index
+  VisitForStackValue(args->at(2));  // value
+  __ pop(rcx);
+  __ pop(rbx);
+  VisitForAccumulatorValue(args->at(0));  // string
+
+  static const String::Encoding encoding = String::ONE_BYTE_ENCODING;
+  SeqStringSetCharGenerator::Generate(masm_, encoding, rax, rbx, rcx);
+  context()->Plug(rax);
+}
+
+
+void FullCodeGenerator::EmitTwoByteSeqStringSetChar(CallRuntime* expr) {
+  ZoneList<Expression*>* args = expr->arguments();
+  ASSERT_EQ(3, args->length());
+
+  VisitForStackValue(args->at(1));  // index
+  VisitForStackValue(args->at(2));  // value
+  __ pop(rcx);
+  __ pop(rbx);
+  VisitForAccumulatorValue(args->at(0));  // string
+
+  static const String::Encoding encoding = String::TWO_BYTE_ENCODING;
+  SeqStringSetCharGenerator::Generate(masm_, encoding, rax, rbx, rcx);
+  context()->Plug(rax);
+}
+
+
 void FullCodeGenerator::EmitMathPow(CallRuntime* expr) {
   // Load the arguments on the stack and call the runtime function.
   ZoneList<Expression*>* args = expr->arguments();
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index 3f01d3b..0e5c99b 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -1533,6 +1533,15 @@ void LCodeGen::DoDateField(LDateField* instr) {
 }
 
 
+void LCodeGen::DoSeqStringSetChar(LSeqStringSetChar* instr) {
+  SeqStringSetCharGenerator::Generate(masm(),
+                                      instr->encoding(),
+                                      ToRegister(instr->string()),
+                                      ToRegister(instr->index()),
+                                      ToRegister(instr->value()));
+}
+
+
 void LCodeGen::DoBitNotI(LBitNotI* instr) {
   LOperand* input = instr->value();
   ASSERT(input->Equals(instr->result()));
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index defdafa..919d074 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -1583,6 +1583,17 @@ LInstruction* LChunkBuilder::DoDateField(HDateField* instr) {
 }
 
 
+LInstruction* LChunkBuilder::DoSeqStringSetChar(HSeqStringSetChar* instr) {
+  LOperand* string = UseRegister(instr->string());
+  LOperand* index = UseRegister(instr->index());
+  ASSERT(rcx.is_byte_register());
+  LOperand* value = UseFixed(instr->value(), rcx);
+  LSeqStringSetChar* result =
+      new(zone()) LSeqStringSetChar(instr->encoding(), string, index, value);
+  return DefineSameAsFirst(result);
+}
+
+
 LInstruction* LChunkBuilder::DoBoundsCheck(HBoundsCheck* instr) {
   LOperand* value = UseRegisterOrConstantAtStart(instr->index());
   LOperand* length = Use(instr->length());
diff --git a/src/x64/lithium-x64.h b/src/x64/lithium-x64.h
index b37d2ac..f5f0250 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -149,6 +149,7 @@ class LCodeGen;
   V(Random)                                     \
   V(RegExpLiteral)                              \
   V(Return)                                     \
+  V(SeqStringSetChar)                           \
   V(ShiftI)                                     \
   V(SmiTag)                                     \
   V(SmiUntag)                                   \
@@ -1160,6 +1161,30 @@ class LDateField: public LTemplateInstruction<1, 1, 0> {
 };
 
 
+class LSeqStringSetChar: public LTemplateInstruction<1, 3, 0> {
+ public:
+  LSeqStringSetChar(String::Encoding encoding,
+                    LOperand* string,
+                    LOperand* index,
+                    LOperand* value) : encoding_(encoding) {
+    inputs_[0] = string;
+    inputs_[1] = index;
+    inputs_[2] = value;
+  }
+
+  String::Encoding encoding() { return encoding_; }
+  LOperand* string() { return inputs_[0]; }
+  LOperand* index() { return inputs_[1]; }
+  LOperand* value() { return inputs_[2]; }
+
+  DECLARE_CONCRETE_INSTRUCTION(SeqStringSetChar, "seq-string-set-char")
+  DECLARE_HYDROGEN_ACCESSOR(SeqStringSetChar)
+
+ private:
+  String::Encoding encoding_;
+};
+
+
 class LThrow: public LTemplateInstruction<0, 1, 0> {
  public:
   explicit LThrow(LOperand* value) {
diff --git a/test/mjsunit/fuzz-natives-part1.js b/test/mjsunit/fuzz-natives-part1.js
index 29a2abb..f459126 100644
--- a/test/mjsunit/fuzz-natives-part1.js
+++ b/test/mjsunit/fuzz-natives-part1.js
@@ -198,6 +198,8 @@ var knownProblems = {
   // Only applicable to strings.
   "_HasCachedArrayIndex": true,
   "_GetCachedArrayIndex": true,
+  "_OneByteSeqStringSetChar": true,
+  "_TwoByteSeqStringSetChar": true,
 
   // Only for debugging parallel recompilation.
   "InstallRecompiledCode": true,
diff --git a/test/mjsunit/fuzz-natives-part2.js b/test/mjsunit/fuzz-natives-part2.js
index 6fb8df1..2faad1d 100644
--- a/test/mjsunit/fuzz-natives-part2.js
+++ b/test/mjsunit/fuzz-natives-part2.js
@@ -196,7 +196,13 @@ var knownProblems = {
 
   // Only applicable to strings.
   "_HasCachedArrayIndex": true,
-  "_GetCachedArrayIndex": true
+  "_GetCachedArrayIndex": true,
+  "_OneByteSeqStringSetChar": true,
+  "_TwoByteSeqStringSetChar": true,
+
+  // Only for debugging parallel recompilation.
+  "InstallRecompiledCode": true,
+  "ForceParallelRecompile": true
 };
 
 var currentlyUncallable = {
diff --git a/test/mjsunit/fuzz-natives-part3.js b/test/mjsunit/fuzz-natives-part3.js
index df9bb7e..ed71d33 100644
--- a/test/mjsunit/fuzz-natives-part3.js
+++ b/test/mjsunit/fuzz-natives-part3.js
@@ -196,7 +196,13 @@ var knownProblems = {
 
   // Only applicable to strings.
   "_HasCachedArrayIndex": true,
-  "_GetCachedArrayIndex": true
+  "_GetCachedArrayIndex": true,
+  "_OneByteSeqStringSetChar": true,
+  "_TwoByteSeqStringSetChar": true,
+
+  // Only for debugging parallel recompilation.
+  "InstallRecompiledCode": true,
+  "ForceParallelRecompile": true
 };
 
 var currentlyUncallable = {
diff --git a/test/mjsunit/fuzz-natives-part4.js b/test/mjsunit/fuzz-natives-part4.js
index c340619..1b128d5 100644
--- a/test/mjsunit/fuzz-natives-part4.js
+++ b/test/mjsunit/fuzz-natives-part4.js
@@ -196,7 +196,13 @@ var knownProblems = {
 
   // Only applicable to strings.
   "_HasCachedArrayIndex": true,
-  "_GetCachedArrayIndex": true
+  "_GetCachedArrayIndex": true,
+  "_OneByteSeqStringSetChar": true,
+  "_TwoByteSeqStringSetChar": true,
+
+  // Only for debugging parallel recompilation.
+  "InstallRecompiledCode": true,
+  "ForceParallelRecompile": true
 };
 
 var currentlyUncallable = {
diff --git a/test/mjsunit/regress/regress-json-stringify-gc.js b/test/mjsunit/regress/regress-json-stringify-gc.js
index d732ebc..c0a71bf 100644
--- a/test/mjsunit/regress/regress-json-stringify-gc.js
+++ b/test/mjsunit/regress/regress-json-stringify-gc.js
@@ -37,5 +37,5 @@ for (var i = 0; i < 10000; i++) a.push(new_space_string);
 // screw up reading from the correct location.
 json1 = JSON.stringify(a);
 json2 = JSON.stringify(a);
-assertEquals(json1, json2, "GC caused JSON.stringify to fail.");
+assertTrue(json1 == json2, "GC caused JSON.stringify to fail.");
 
diff --git a/test/mjsunit/string-natives.js b/test/mjsunit/string-natives.js
new file mode 100644
index 0000000..b1ec875
--- /dev/null
+++ b/test/mjsunit/string-natives.js
@@ -0,0 +1,72 @@
+// Copyright 2012 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Flags: --expose-gc --allow-natives-syntax
+
+function test() {
+  var s1 = %NewString(26, true);
+  for (i = 0; i < 26; i++) %_OneByteSeqStringSetChar(s1, i, i+65);
+  assertEquals("ABCDEFGHIJKLMNOPQRSTUVWXYZ", s1);
+  s1 = %TruncateString(s1, 13);
+  assertEquals("ABCDEFGHIJKLM", s1);
+
+  var s2 = %NewString(26, false);
+  for (i = 0; i < 26; i++) %_TwoByteSeqStringSetChar(s2, i, i+65);
+  assertEquals("ABCDEFGHIJKLMNOPQRSTUVWXYZ", s2);
+  s2 = %TruncateString(s1, 13);
+  assertEquals("ABCDEFGHIJKLM", s2);
+
+  var s3 = %NewString(26, false);
+  for (i = 0; i < 26; i++) %_TwoByteSeqStringSetChar(s3, i, i+1000);
+  for (i = 0; i < 26; i++) assertEquals(s3[i], String.fromCharCode(i+1000));
+
+  var a = [];
+  for (var i = 0; i < 1000; i++) {
+    var s = %NewString(10000, i % 2 == 1);
+    a.push(s);
+  }
+
+  gc();
+
+  for (var i = 0; i < 1000; i++) {
+    assertEquals(10000, a[i].length);
+    a[i] = %TruncateString(a[i], 5000);
+  }
+
+  gc();
+
+  for (var i = 0; i < 1000; i++) {
+    assertEquals(5000, a[i].length);
+  }
+}
+
+
+test();
+test();
+%OptimizeFunctionOnNextCall(test);
+test();
+
diff --git a/test/mjsunit/uri.js b/test/mjsunit/uri.js
index 178ff1f..fae349f 100644
--- a/test/mjsunit/uri.js
+++ b/test/mjsunit/uri.js
@@ -76,3 +76,15 @@ assertEquals(cc8_2, decodeURI(encodeURI(s8)).charCodeAt(1));
 assertEquals(cc9_1, decodeURI(encodeURI(s9)).charCodeAt(0));
 assertEquals(cc9_2, decodeURI(encodeURI(s9)).charCodeAt(1));
 assertEquals(cc10, decodeURI(encodeURI(s10)).charCodeAt(0));
+
+assertEquals("", decodeURI(""));
+assertEquals("", encodeURI(""));
+
+function test(string) {
+  assertEquals(string, decodeURI(encodeURI(string)));
+}
+
+test("\u1234\u0123\uabcd");
+test("abcd");
+test("ab<\u1234\u0123");
+test("ab\u1234<\u0123");