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

src/mips/macro-assembler-mips.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 4874 matching lines @@
   // Otherwise it's String::kHeaderSize + string->length() * (1 or 2).
   // External strings are the only ones with the kExternalStringTag bit
   // set.
   ASSERT_EQ(0, kSeqStringTag & kExternalStringTag);
   ASSERT_EQ(0, kConsStringTag & kExternalStringTag);
   And(t8, instance_type, Operand(kExternalStringTag));
   {
     Label skip;
     Branch(&skip, eq, t8, Operand(zero_reg));
     li(length, ExternalString::kSize);
+    And(t8, instance_type, Operand(kBufferedStringTag));
+    Branch(&is_data_object, eq, t8, Operand(zero_reg));
+    li(length, ExternalString::kExtendedSize);
     Branch(&is_data_object);
     bind(&skip);
   }
 
   // Sequential string, either ASCII or UC16.
   // For ASCII (char-size of 1) we shift the smi tag away to get the length.
   // For UC16 (char-size of 2) we just leave the smi tag in place, thereby
   // getting the length multiplied by 2.
   ASSERT(kAsciiStringTag == 4 && kStringEncodingMask == 4);
   ASSERT(kSmiTag == 0 && kSmiTagSize == 1);
@@ skipping 139 matching lines @@
        opcode == BGTZL);
   opcode = (cond == eq) ? BEQ : BNE;
   instr = (instr & ~kOpcodeMask) | opcode;
   masm_.emit(instr);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS