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

src/ia32/code-stubs-ia32.cc

Index: src/ia32/code-stubs-ia32.cc
diff --git a/src/ia32/code-stubs-ia32.cc b/src/ia32/code-stubs-ia32.cc
index 23bea4f8568ce2cebeccf8212be82343e75e4d29..060bf5a8c696d96c6b6437ab87c58e5c0d16e1ab 100644
--- a/src/ia32/code-stubs-ia32.cc
+++ b/src/ia32/code-stubs-ia32.cc
@@ -5089,11 +5089,6 @@ void CompareStub::PrintName(StringStream* stream) {
 // StringCharCodeAtGenerator
 
 void StringCharCodeAtGenerator::GenerateFast(MacroAssembler* masm) {
-  Label flat_string;
-  Label ascii_string;
-  Label got_char_code;
-  Label sliced_string;
-
   // If the receiver is a smi trigger the non-string case.
   STATIC_ASSERT(kSmiTag == 0);
   __ JumpIfSmi(object_, receiver_not_string_);
@@ -5114,73 +5109,137 @@ void StringCharCodeAtGenerator::GenerateFast(MacroAssembler* masm) {
   __ cmp(index_, FieldOperand(object_, String::kLengthOffset));
   __ j(above_equal, index_out_of_range_);
 
-  // We need special handling for non-flat strings.
-  STATIC_ASSERT(kSeqStringTag == 0);
-  __ test(result_, Immediate(kStringRepresentationMask));
-  __ j(zero, &flat_string);
+  __ SmiUntag(index_);
 
-  // Handle non-flat strings.
-  __ and_(result_, kStringRepresentationMask);
-  STATIC_ASSERT(kConsStringTag < kExternalStringTag);
-  STATIC_ASSERT(kSlicedStringTag > kExternalStringTag);
-  __ cmp(result_, kExternalStringTag);
-  __ j(greater, &sliced_string, Label::kNear);
-  __ j(equal, &call_runtime_);
+  Factory* factory = masm->isolate()->factory();
+  GenerateCharLoad(masm, factory, object_, index_, result_, &call_runtime_);
+
+  __ SmiTag(result_);
+  __ bind(&exit_);
+}
+
+
+void StringCharCodeAtGenerator::GenerateCharLoad(MacroAssembler* masm,
+                                                 Factory* factory,
+                                                 Register string,
+                                                 Register index,
+                                                 Register result,
+                                                 Label* call_runtime) {
+  // Fetch the instance type of the receiver into result register.
+  __ mov(result, FieldOperand(string, HeapObject::kMapOffset));
+  __ movzx_b(result, FieldOperand(result, Map::kInstanceTypeOffset));
+
+  // We need special handling for indirect strings.
+  Label check_sequential;
+  __ test(result, Immediate(kIsIndirectStringMask));
+  __ j(zero, &check_sequential);
+
+  // Dispatch on the indirect string shape: slice or cons.
+  Label cons_string;
+  __ test(result, Immediate(kSlicedNotConsMask));
+  __ j(zero, &cons_string);
+
+  // Handle slices.
+  Label indirect_string_loaded;
+  __ mov(result, FieldOperand(string, SlicedString::kOffsetOffset));
+  __ SmiUntag(result);
+  __ add(index, result);
+  __ mov(string, FieldOperand(string, SlicedString::kParentOffset));
+  __ jmp(&indirect_string_loaded);
+
+  // Handle external strings.
+  Label external_string, two_byte_external, done, revert_index_call_runtime;
+  __ bind(&external_string);
+  if (FLAG_debug_code) {
+    // Assert that we do not have a cons or slice (indirect strings) here.
+    __ test(result, Immediate(kIsIndirectStringMask));
+    __ Assert(zero, "external string expected, but not found");
+  }
+  __ test(result, Immediate(kBufferedStringMask));
+  __ j(zero, call_runtime);
+  __ mov(result, FieldOperand(string, ExternalString::kBufferIndexOffset));
+  __ SmiUntag(result);
+  __ sub(index, result);
+  __ j(negative, &revert_index_call_runtime);
+
+  __ cmp(FieldOperand(string, HeapObject::kMapOffset),
+         Immediate(factory->external_buffered_string_map()));
+  __ j(equal, &two_byte_external, Label::kNear);
+  __ cmp(FieldOperand(string, HeapObject::kMapOffset),
+         Immediate(factory->external_buffered_symbol_map()));
+  __ j(equal, &two_byte_external, Label::kNear);
+
+  // Ascii string.
+  __ cmp(index, Immediate(ExternalAsciiString::kBufferedChars));
+  __ j(greater_equal, &revert_index_call_runtime);
+  __ movzx_b(result, FieldOperand(string,
+                                  index,
+                                  times_1,
+                                  ExternalString::kBufferContentOffset));
+  __ jmp(&done);
+
+  __ bind(&two_byte_external);
+  // Two-byte string.
+  __ cmp(index, Immediate(ExternalTwoByteString::kBufferedChars));
+  __ j(greater_equal, &revert_index_call_runtime);
+  __ movzx_w(result, FieldOperand(string,
+                                  index,
+                                  times_2,
+                                  ExternalString::kBufferContentOffset));
+  __ jmp(&done);
+  __ bind(&revert_index_call_runtime);
+  __ add(index, result);
+  __ jmp(call_runtime);
 
-  // ConsString.
+  // Handle conses.
   // Check whether the right hand side is the empty string (i.e. if
   // this is really a flat string in a cons string). If that is not
   // the case we would rather go to the runtime system now to flatten
   // the string.
-  Label assure_seq_string;
-  __ cmp(FieldOperand(object_, ConsString::kSecondOffset),
-         Immediate(masm->isolate()->factory()->empty_string()));
-  __ j(not_equal, &call_runtime_);
-  // Get the first of the two parts.
-  __ mov(object_, FieldOperand(object_, ConsString::kFirstOffset));
-  __ jmp(&assure_seq_string, Label::kNear);
-
-  // SlicedString, unpack and add offset.
-  __ bind(&sliced_string);
-  __ add(index_, FieldOperand(object_, SlicedString::kOffsetOffset));
-  __ mov(object_, FieldOperand(object_, SlicedString::kParentOffset));
-
-  // Assure that we are dealing with a sequential string. Go to runtime if not.
+  __ bind(&cons_string);
+  __ cmp(FieldOperand(string, ConsString::kSecondOffset),
+         Immediate(factory->empty_string()));
+  __ j(not_equal, call_runtime);
+  __ mov(string, FieldOperand(string, ConsString::kFirstOffset));
+
+  __ bind(&indirect_string_loaded);
+  __ mov(result, FieldOperand(string, HeapObject::kMapOffset));
+  __ movzx_b(result, FieldOperand(result, Map::kInstanceTypeOffset));
+
+  // Check whether the string is sequential. The only non-sequential
+  // shapes we support have just been unwrapped above.
   // Note that if the original string is a cons or slice with an external
   // string as underlying string, we pass that unpacked underlying string with
   // the adjusted index to the runtime function.
-  __ bind(&assure_seq_string);
-  __ mov(result_, FieldOperand(object_, HeapObject::kMapOffset));
-  __ movzx_b(result_, FieldOperand(result_, Map::kInstanceTypeOffset));
+  __ bind(&check_sequential);
   STATIC_ASSERT(kSeqStringTag == 0);
-  __ test(result_, Immediate(kStringRepresentationMask));
-  __ j(not_zero, &call_runtime_);
+  __ test(result, Immediate(kStringRepresentationMask));
+  __ j(not_zero, &external_string);
 
-  // Check for 1-byte or 2-byte string.
-  __ bind(&flat_string);
+  // Dispatch on the encoding: ASCII or two-byte.
+  Label ascii_string;
   STATIC_ASSERT((kStringEncodingMask & kAsciiStringTag) != 0);
   STATIC_ASSERT((kStringEncodingMask & kTwoByteStringTag) == 0);
-  __ test(result_, Immediate(kStringEncodingMask));
+  __ test(result, Immediate(kStringEncodingMask));
   __ j(not_zero, &ascii_string, Label::kNear);
 
-  // 2-byte string.
-  // Load the 2-byte character code into the result register.
+  // Two-byte string.
+  // Load the two-byte character code into the result register.
   STATIC_ASSERT(kSmiTag == 0 && kSmiTagSize == 1);
-  __ movzx_w(result_, FieldOperand(object_,
-                                   index_, times_1,  // Scratch is smi-tagged.
-                                   SeqTwoByteString::kHeaderSize));
-  __ jmp(&got_char_code, Label::kNear);
+  __ movzx_w(result, FieldOperand(string,
+                                  index,
+                                  times_2,
+                                  SeqTwoByteString::kHeaderSize));
+  __ jmp(&done, Label::kNear);
 
-  // ASCII string.
+  // Ascii string.
   // Load the byte into the result register.
   __ bind(&ascii_string);
-  __ SmiUntag(index_);
-  __ movzx_b(result_, FieldOperand(object_,
-                                   index_, times_1,
-                                   SeqAsciiString::kHeaderSize));
-  __ bind(&got_char_code);
-  __ SmiTag(result_);
-  __ bind(&exit_);
+  __ movzx_b(result, FieldOperand(string,
+                                  index,
+                                  times_1,
+                                  SeqAsciiString::kHeaderSize));
+  __ bind(&done);
 }
 
 
@@ -5228,6 +5287,7 @@ void StringCharCodeAtGenerator::GenerateSlow(
   __ bind(&call_runtime_);
   call_helper.BeforeCall(masm);
   __ push(object_);
+  __ SmiTag(index_);
   __ push(index_);
   __ CallRuntime(Runtime::kStringCharCodeAt, 2);
   if (!result_.is(eax)) {