Tentative implementation of string slices (hidden under the flag --string-slices).

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 53a3183694cbfdfc87f16524888036e27d434d14..7014a6de93ca68266645093414e8992e671ff693 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -184,6 +184,15 @@ bool Object::IsConsString() {
 }
 
 
+bool Object::IsSlicedString() {
+  if (!this->IsHeapObject()) return false;
+  uint32_t type = HeapObject::cast(this)->map()->instance_type();
+  uint32_t representation =

[antonm, 2011/07/27 14:04:49]

if you don't want to introduce helper function which can be reused by both
IsConstStrng and IsSlicedString, I think they should be as similar as possible.

+      type & (kIsNotStringMask | kStringRepresentationMask);
+  return representation == (kStringTag | kSlicedStringTag);
+}
+
+
 bool Object::IsSeqString() {
   if (!IsString()) return false;
   return StringShape(String::cast(this)).IsSequential();
@@ -280,6 +289,11 @@ bool StringShape::IsCons() {
 }
 
 
+bool StringShape::IsSliced() {
+  return (type_ & kStringRepresentationMask) == kSlicedStringTag;
+}
+
+
 bool StringShape::IsExternal() {
   return (type_ & kStringRepresentationMask) == kExternalStringTag;
 }
@@ -2041,6 +2055,7 @@ CAST_ACCESSOR(String)
 CAST_ACCESSOR(SeqString)
 CAST_ACCESSOR(SeqAsciiString)
 CAST_ACCESSOR(SeqTwoByteString)
+CAST_ACCESSOR(SlicedString)
 CAST_ACCESSOR(ConsString)
 CAST_ACCESSOR(ExternalString)
 CAST_ACCESSOR(ExternalAsciiString)
@@ -2156,6 +2171,9 @@ uint16_t String::Get(int index) {
       return ExternalAsciiString::cast(this)->ExternalAsciiStringGet(index);
     case kExternalStringTag | kTwoByteStringTag:
       return ExternalTwoByteString::cast(this)->ExternalTwoByteStringGet(index);
+    case kSlicedStringTag | kAsciiStringTag:
+    case kSlicedStringTag | kTwoByteStringTag:
+      return SlicedString::cast(this)->SlicedStringGet(index);
     default:
       break;
   }
@@ -2188,6 +2206,12 @@ bool String::IsFlat() {
 }
 
 
+bool String::IsIndirect() {
+  uint32_t representation = StringShape(this).representation_tag();
+  return (representation & kIsIndirectStringMask) == kIsIndirectStringTag;
+}
+
+
 uint16_t SeqAsciiString::SeqAsciiStringGet(int index) {
   ASSERT(index >= 0 && index < length());
   return READ_BYTE_FIELD(this, kHeaderSize + index * kCharSize);
@@ -2243,6 +2267,20 @@ int SeqAsciiString::SeqAsciiStringSize(InstanceType instance_type) {
 }
 
 
+String* SlicedString::parent() {
+  return String::cast(READ_FIELD(this, kParentOffset));
+}
+
+
+void SlicedString::set_parent(String* parent) {
+  ASSERT(parent->IsSeqString());
+  WRITE_FIELD(this, kParentOffset, parent);
+}
+
+
+SMI_ACCESSORS(SlicedString, offset, kOffsetOffset)
+
+
 String* ConsString::first() {
   return String::cast(READ_FIELD(this, kFirstOffset));
 }