In MacroAssembler::JumpIfNotBothSequentialAsciiStrings a custom mask

src/arm/macro-assembler-arm.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
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 // 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
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@@ skipping 3244 matching lines @@
 
 
 void MacroAssembler::JumpIfBothInstanceTypesAreNotSequentialAscii(
     Register first,
     Register second,
     Register scratch1,
     Register scratch2,
     Label* failure) {
   int kFlatAsciiStringMask =
       kIsNotStringMask | kStringEncodingMask | kStringRepresentationMask;
-  int kFlatAsciiStringTag = ASCII_STRING_TYPE;
+  // Use ASCII_INTERNALIZED_STRING_TYPE because it's internalized bit is zero.
+  // Since we don't include that bit in the mask above, the test below will
+  // succeed for ASCII_STRING_TYPE and ASCII_INTERNALIZED_STRING_TYPE.
+  STATIC_ASSERT(kInternalizedTag == 0);
+  const int kFlatAsciiStringTag = ASCII_INTERNALIZED_STRING_TYPE;

[Yang, 2013/07/22 09:09:46]

I actually prefer not to use the defined instance type, but instead something
corresponding to the mask:

kStringTag | kOneByteStringTag | kSeqStringTag

[mvstanton, 2013/07/22 09:40:17]

Done.

   and_(scratch1, first, Operand(kFlatAsciiStringMask));
   and_(scratch2, second, Operand(kFlatAsciiStringMask));
   cmp(scratch1, Operand(kFlatAsciiStringTag));
   // Ignore second test if first test failed.
   cmp(scratch2, Operand(kFlatAsciiStringTag), eq);
   b(ne, failure);
 }
 
 
 void MacroAssembler::JumpIfInstanceTypeIsNotSequentialAscii(Register type,
                                                             Register scratch,
                                                             Label* failure) {
   int kFlatAsciiStringMask =
       kIsNotStringMask | kStringEncodingMask | kStringRepresentationMask;
   int kFlatAsciiStringTag = ASCII_STRING_TYPE;

[Yang, 2013/07/22 09:09:46]

I believe this suffers from the same issue!

[mvstanton, 2013/07/22 09:40:17]

Grr. Removed defined instance check here too, thanks.

   and_(scratch, type, Operand(kFlatAsciiStringMask));
   cmp(scratch, Operand(kFlatAsciiStringTag));
   b(ne, failure);
 }
 
 static const int kRegisterPassedArguments = 4;
 
 
 int MacroAssembler::CalculateStackPassedWords(int num_reg_arguments,
                                               int num_double_arguments) {
@@ skipping 540 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