Speed up charCodeAt on very large cons strings, by insisting on...

src/ia32/codegen-ia32.cc

 // Copyright 2006-2009 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 4813 matching lines @@
   __ shl(temp.reg(), kSmiTagSize);
   __ jmp(&end);
 
   // Handle non-flat strings.
   __ bind(&not_a_flat_string);
   __ and_(temp.reg(), kStringRepresentationMask);
   __ cmp(temp.reg(), kConsStringTag);
   __ j(not_equal, &slow_case);
 
   // ConsString.
+  // Check that the right hand side is the empty string (ie if this is really a
+  // flat string in a cons string).  If that is not the case we would rather go
+  // to the runtime system now, to flatten the string.
+  __ mov(temp.reg(), FieldOperand(object.reg(), ConsString::kSecondOffset));
+  __ cmp(Operand(temp.reg()), Immediate(Handle<String>(Heap::empty_string())));
+  __ j(not_equal, &slow_case);
   // Get the first of the two strings.
   __ mov(object.reg(), FieldOperand(object.reg(), ConsString::kFirstOffset));
   __ jmp(&try_again_with_new_string);
 
   __ bind(&slow_case);
   // Move the undefined value into the result register, which will
   // trigger the slow case.
   __ Set(temp.reg(), Immediate(Factory::undefined_value()));
 
   __ bind(&end);
@@ skipping 3282 matching lines @@
 
 int CompareStub::MinorKey() {
   // Encode the two parameters in a unique 16 bit value.
   ASSERT(static_cast<unsigned>(cc_) < (1 << 15));
   return (static_cast<unsigned>(cc_) << 1) | (strict_ ? 1 : 0);
 }
 
 #undef __
 
 } }  // namespace v8::internal