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

src/arm/macro-assembler-arm.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 3468 matching lines @@
   tst(instance_type, Operand(kIsIndirectStringMask | kIsNotStringMask));
   b(ne, 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).
   // External strings are the only ones with the kExternalStringTag bit
   // set.
   ASSERT_EQ(0, kSeqStringTag & kExternalStringTag);
   ASSERT_EQ(0, kConsStringTag & kExternalStringTag);
   tst(instance_type, Operand(kExternalStringTag));
-  mov(length, Operand(ExternalString::kSize), LeaveCC, ne);
-  b(ne, &is_data_object);
+  Label not_external_string;
+  b(eq, &not_external_string);
+  tst(instance_type, Operand(kBufferedStringTag));
+  mov(length, Operand(ExternalString::kSize), LeaveCC, eq);
+  mov(length, Operand(ExternalString::kExtendedSize), LeaveCC, ne);
+  b(&is_data_object);
+  bind(&not_external_string);
 
   // 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);
   ldr(ip, FieldMemOperand(value, String::kLengthOffset));
   tst(instance_type, Operand(kStringEncodingMask));
   mov(ip, Operand(ip, LSR, 1), LeaveCC, ne);
@@ skipping 111 matching lines @@
 void CodePatcher::EmitCondition(Condition cond) {
   Instr instr = Assembler::instr_at(masm_.pc_);
   instr = (instr & ~kCondMask) | cond;
   masm_.emit(instr);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM