Introduce read buffer for external strings when using charAt (ia32).

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 0a3508dcccabf243d24dd5789a784cf73abeb544..ec2b2e48476812c75227e150dc5eb1d5790fb1cd 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -960,26 +960,42 @@ bool String::MakeExternal(v8::String::ExternalStringResource* resource) {
   ASSERT(size >= ExternalString::kSize);
   bool is_ascii = this->IsAsciiRepresentation();
   bool is_symbol = this->IsSymbol();
-  int length = this->length();
-  int hash_field = this->hash_field();
-
-  // Morph the object to an external string by adjusting the map and
-  // reinitializing the fields.
-  this->set_map(is_ascii ?
-                heap->external_string_with_ascii_data_map() :
-                heap->external_string_map());
-  ExternalTwoByteString* self = ExternalTwoByteString::cast(this);
-  self->set_length(length);
-  self->set_hash_field(hash_field);
-  self->set_resource(resource);
-  // Additionally make the object into an external symbol if the original string
-  // was a symbol to start with.
-  if (is_symbol) {
-    self->Hash();  // Force regeneration of the hash value.
-    // Now morph this external string into a external symbol.
-    this->set_map(is_ascii ?
-                  heap->external_symbol_with_ascii_data_map() :
-                  heap->external_symbol_map());
+
+  ExternalTwoByteString* externalized;
+
+  if (this->length() >= ExternalString::kMinBufferedStringLength &&
+      size < ExternalString::kExtendedSize) {
+    ASSERT(this->IsConsString() || this->IsSlicedString());
+    // Cannot morph in place since size is too small.
+    externalized = ExternalTwoByteString::cast(
+        *(heap->isolate()->factory()->NewExternalStringFromTwoByte(resource)));
+    this->set_map(heap->sliced_string_map());
+    SlicedString* self = SlicedString::cast(this);
+    self->set_parent(externalized);
+    self->set_offset(0);
+  } else {
+    // Morph the string to an external string in place.
+    if (this->length() < ExternalString::kMinBufferedStringLength) {
+      this->set_map(
+          is_ascii ? (is_symbol ? heap->external_symbol_with_ascii_data_map()
+                                : heap->external_string_with_ascii_data_map())
+                   : (is_symbol ? heap->external_symbol_map()
+                                : heap->external_string_map()));
+    } else {
+      this->set_map(
+          is_ascii
+              ? (is_symbol
+                     ? heap->external_buffered_symbol_with_ascii_data_map()
+                     : heap->external_buffered_string_with_ascii_data_map())
+              : (is_symbol ? heap->external_buffered_symbol_map()
+                           : heap->external_buffered_string_map()));
+    }
+    externalized = ExternalTwoByteString::cast(this);
+    externalized->set_resource(resource);
+    if (is_symbol) externalized->Hash();  // Force rehashing.
+    if (externalized->IsBuffered()) {
+      externalized->set_buffer_index(ExternalString::kInvalidBufferIndex);
+    }
   }
 
   // Fill the remainder of the string with dead wood.
@@ -1013,22 +1029,34 @@ bool String::MakeExternal(v8::String::ExternalAsciiStringResource* resource) {
   }
   ASSERT(size >= ExternalString::kSize);
   bool is_symbol = this->IsSymbol();
-  int length = this->length();
-  int hash_field = this->hash_field();
-
-  // Morph the object to an external string by adjusting the map and
-  // reinitializing the fields.
-  this->set_map(heap->external_ascii_string_map());
-  ExternalAsciiString* self = ExternalAsciiString::cast(this);
-  self->set_length(length);
-  self->set_hash_field(hash_field);
-  self->set_resource(resource);
-  // Additionally make the object into an external symbol if the original string
-  // was a symbol to start with.
-  if (is_symbol) {
-    self->Hash();  // Force regeneration of the hash value.
-    // Now morph this external string into a external symbol.
-    this->set_map(heap->external_ascii_symbol_map());
+
+  ExternalAsciiString* externalized;
+
+  if (this->length() >= ExternalString::kMinBufferedStringLength &&
+      size < ExternalString::kExtendedSize) {
+    ASSERT(this->IsConsString() || this->IsSlicedString());
+    // Cannot morph in place since size is too small.
+    externalized = ExternalAsciiString::cast(
+        *(heap->isolate()->factory()->NewExternalStringFromAscii(resource)));
+    this->set_map(heap->sliced_ascii_string_map());
+    SlicedString* self = SlicedString::cast(this);
+    self->set_parent(externalized);
+    self->set_offset(0);
+  } else {
+    // Morph the string to an external string in place.
+    if (this->length() < ExternalString::kMinBufferedStringLength) {
+      this->set_map(is_symbol ? heap->external_ascii_symbol_map()
+                              : heap->external_ascii_string_map());
+    } else {
+      this->set_map(is_symbol ? heap->external_buffered_ascii_symbol_map()
+                              : heap->external_buffered_ascii_string_map());
+    }
+    externalized = ExternalAsciiString::cast(this);
+    externalized->set_resource(resource);
+    if (is_symbol) externalized->Hash();  // Force rehashing.
+    if (externalized->IsBuffered()) {
+      externalized->set_buffer_index(ExternalString::kInvalidBufferIndex);
+    }
   }
 
   // Fill the remainder of the string with dead wood.
@@ -6032,9 +6060,18 @@ const unibrow::byte* ConsString::ConsStringReadBlock(ReadBlockBuffer* rbb,
 }
 
 
-uint16_t ExternalAsciiString::ExternalAsciiStringGet(int index) {
+uint16_t ExternalAsciiString::ExternalAsciiStringGet(
+    int index, ExternalStringBufferFlag flag) {
   ASSERT(index >= 0 && index < length());
-  return resource()->data()[index];
+  const char* source = resource()->data();
+  if (flag == UPDATE_EXTERNAL_STRING_BUFFER && IsBuffered()) {
+    int buffer_start = Max(0, index - kBackwardBufferedChars);
+    int buffer_end = Min(length(), index + kForwardBufferedChars);
+    int size = (buffer_end - buffer_start) * kASCIISize;
+    set_buffer_index(buffer_start);
+    memcpy(buffer(), source + buffer_start, size);
+  }
+  return *(source + index);
 }
 
 
@@ -6057,9 +6094,18 @@ const uc16* ExternalTwoByteString::ExternalTwoByteStringGetData(
 }
 
 
-uint16_t ExternalTwoByteString::ExternalTwoByteStringGet(int index) {
+uint16_t ExternalTwoByteString::ExternalTwoByteStringGet(
+    int index, ExternalStringBufferFlag flag) {
   ASSERT(index >= 0 && index < length());
-  return resource()->data()[index];
+  const uint16_t* source = resource()->data();
+  if (flag == UPDATE_EXTERNAL_STRING_BUFFER && IsBuffered()) {
+    int buffer_start = Max(0, index - kBackwardBufferedChars);
+    int buffer_end = Min(length(), index + kForwardBufferedChars);
+    int size = (buffer_end - buffer_start) * kUC16Size;
+    set_buffer_index(buffer_start);
+    memcpy(buffer(), source + buffer_start, size);
+  }
+  return *(source + index);
 }
 
 
@@ -6490,13 +6536,14 @@ void ConsString::ConsStringReadBlockIntoBuffer(ReadBlockBuffer* rbb,
 }
 
 
-uint16_t ConsString::ConsStringGet(int index) {
+uint16_t ConsString::ConsStringGet(
+    int index, ExternalStringBufferFlag flag) {
   ASSERT(index >= 0 && index < this->length());
 
   // Check for a flattened cons string
   if (second()->length() == 0) {
     String* left = first();
-    return left->Get(index);
+    return left->Get(index, flag);
   }
 
   String* string = String::cast(this);
@@ -6512,7 +6559,7 @@ uint16_t ConsString::ConsStringGet(int index) {
         string = cons_string->second();
       }
     } else {
-      return string->Get(index);
+      return string->Get(index, flag);
     }
   }
 
@@ -6521,8 +6568,9 @@ uint16_t ConsString::ConsStringGet(int index) {
 }
 
 
-uint16_t SlicedString::SlicedStringGet(int index) {
-  return parent()->Get(offset() + index);
+uint16_t SlicedString::SlicedStringGet(
+    int index, ExternalStringBufferFlag flag) {
+  return parent()->Get(offset() + index, flag);
 }