Added a few sanity-assertions about flat strings underlying buffers.

src/regexp-macro-assembler-ia32.cc

 // Copyright 2008-2009 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 954 matching lines @@
 
   // No allocations before calling the regexp, but we can't use
   // AssertNoAllocation, since regexps might be preempted, and another thread
   // might do allocation anyway.
 
   String* subject_ptr = *subject;
   // Character offsets into string.
   int start_offset = previous_index;
   int end_offset = subject_ptr->length();
 
+  bool is_ascii = StringShape(*subject).IsAsciiRepresentation();
+
   if (StringShape(subject_ptr).IsCons()) {
     subject_ptr = ConsString::cast(subject_ptr)->first();
   } else if (StringShape(subject_ptr).IsSliced()) {
     SlicedString* slice = SlicedString::cast(subject_ptr);
     start_offset += slice->start();
     end_offset += slice->start();
     subject_ptr = slice->buffer();
   }
-
+  // Ensure that an underlying string has the same ascii-ness.
+  ASSERT(StringShape(subject_ptr).IsAsciiRepresentation() == is_ascii);
+  ASSERT(subject_ptr->IsExternalString() || subject_ptr->IsSeqString());
   // String is now either Sequential or External
-  bool is_ascii = StringShape(*subject).IsAsciiRepresentation();
   int char_size_shift = is_ascii ? 0 : 1;
   int char_length = end_offset - start_offset;
 
   const byte* input_start =
       StringCharacterPosition(subject_ptr, start_offset);
   int byte_length = char_length << char_size_shift;
   const byte* input_end = input_start + byte_length;
   RegExpMacroAssemblerIA32::Result res = Execute(*regexp_code,
                                                  subject_ptr,
                                                  start_offset,
@@ skipping 380 matching lines @@
 
 
 void RegExpMacroAssemblerIA32::LoadConstantBufferAddress(Register reg,
                                                          ArraySlice* buffer) {
   __ mov(reg, buffer->array());
   __ add(Operand(reg), Immediate(buffer->base_offset()));
 }
 
 #undef __
 }}  // namespace v8::internal