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

src/ia32/macro-assembler-ia32.cc

 // Copyright 2011 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
@@ skipping 2560 matching lines @@
   ASSERT(strcmp(Marking::kWhiteBitPattern, "00") == 0);
   ASSERT(strcmp(Marking::kBlackBitPattern, "10") == 0);
   ASSERT(strcmp(Marking::kGreyBitPattern, "11") == 0);
   ASSERT(strcmp(Marking::kImpossibleBitPattern, "01") == 0);
 
   Label done;
 
   // Since both black and grey have a 1 in the first position and white does
   // not have a 1 there we only need to check one bit.
   test(mask_scratch, Operand(bitmap_scratch, MemoryChunk::kHeaderSize));
-  j(not_zero, &done, Label::kNear);
 
   if (FLAG_debug_code) {
+    j(not_zero, &done);
     // Check for impossible bit pattern.
     Label ok;
     push(mask_scratch);
     // shl.  May overflow making the check conservative.
     add(mask_scratch, mask_scratch);
     test(mask_scratch, Operand(bitmap_scratch, MemoryChunk::kHeaderSize));
     j(zero, &ok, Label::kNear);
     int3();
     bind(&ok);
     pop(mask_scratch);
+  } else {
+    j(not_zero, &done, Label::kNear);
   }
 
   // Value is white.  We check whether it is data that doesn't need scanning.
   // Currently only checks for HeapNumber and non-cons strings.
   Register map = ecx;  // Holds map while checking type.
   Register length = ecx;  // Holds length of object after checking type.
   Label not_heap_number;
   Label is_data_object;
 
   // Check for heap-number
@@ skipping 10 matching lines @@
   // If it's a string and it's not a cons string then it's an object containing
   // no GC pointers.
   Register instance_type = ecx;
   movzx_b(instance_type, FieldOperand(map, Map::kInstanceTypeOffset));
   test_b(instance_type, kIsIndirectStringMask | kIsNotStringMask);
   j(not_zero, value_is_white_and_not_data);
   // It's a non-indirect (non-cons and non-slice) string.
   // If it's external, the length is just ExternalString::kSize.
   // Otherwise it's String::kHeaderSize + string->length() * (1 or 2).
   Label not_external;
-  // External strings are the only ones with the kExternalStringTag bit
-  // set.
+  // External strings are the only ones with the kExternalStringTag bit set.
   ASSERT_EQ(0, kSeqStringTag & kExternalStringTag);
   ASSERT_EQ(0, kConsStringTag & kExternalStringTag);
   test_b(instance_type, kExternalStringTag);
   j(zero, &not_external, Label::kNear);
   mov(length, Immediate(ExternalString::kSize));
+  test_b(instance_type, kBufferedStringTag);
+  j(zero, &is_data_object, Label::kNear);
+  mov(length, Immediate(ExternalString::kExtendedSize));
   jmp(&is_data_object, Label::kNear);
 
   bind(&not_external);
   // Sequential string, either ASCII or UC16.
   ASSERT(kAsciiStringTag == 0x04);
   and_(length, Immediate(kStringEncodingMask));
   xor_(length, Immediate(kStringEncodingMask));
   add(length, Immediate(0x04));
   // Value now either 4 (if ASCII) or 8 (if UC16), i.e., char-size shifted
   // by 2. If we multiply the string length as smi by this, it still
@@ skipping 19 matching lines @@
     cmp(length, Operand(bitmap_scratch, MemoryChunk::kSizeOffset));
     Check(less_equal, "Live Bytes Count overflow chunk size");
   }
 
   bind(&done);
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32