Recommit introducing short external strings.

src/ia32/codegen-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 544 matching lines @@
 
   // Handle external strings.
   Label external_string, ascii_external, done;
   __ bind(&external_string);
   if (FLAG_debug_code) {
     // Assert that we do not have a cons or slice (indirect strings) here.
     // Sequential strings have already been ruled out.
     __ test(result, Immediate(kIsIndirectStringMask));
     __ Assert(zero, "external string expected, but not found");
   }
+  // Rule out short external strings.
+  STATIC_CHECK(kShortExternalStringTag != 0);
+  __ test_b(result, kShortExternalStringMask);

[Yang, 2011/11/23 12:56:05]

There is actually no need to reload the instance type since it is still in
|result|.

+  __ j(not_zero, call_runtime);
+  // Check encoding.
+  STATIC_ASSERT(kTwoByteStringTag == 0);
+  __ test_b(result, kStringEncodingMask);
   __ mov(result, FieldOperand(string, ExternalString::kResourceDataOffset));
-  // Assert that the external string has not been finalized yet.
-  __ test(result, result);
-  __ j(zero, call_runtime);
-  Register scratch = string;
-  __ mov(scratch, FieldOperand(string, HeapObject::kMapOffset));
-  __ cmp(scratch, Immediate(factory->external_ascii_string_map()));
-  __ j(equal, &ascii_external, Label::kNear);
-  __ cmp(scratch, Immediate(factory->external_ascii_symbol_map()));
-  __ j(equal, &ascii_external, Label::kNear);
+  __ j(not_equal, &ascii_external, Label::kNear);
   // Two-byte string.
   __ movzx_w(result, Operand(result, index, times_2, 0));
   __ jmp(&done);
   __ bind(&ascii_external);
   // Ascii string.
   __ movzx_b(result, Operand(result, index, times_1, 0));
   __ jmp(&done);
 
   // Handle conses.
   // Check whether the right hand side is the empty string (i.e. if
@@ skipping 44 matching lines @@
                                   times_1,
                                   SeqAsciiString::kHeaderSize));
   __ bind(&done);
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32