Limit number of fields in instance to be considered for scalar replacement

I stumbled upon a test that we have (gc/TestBigObj.java) that has an object with 64k fields and that is scalar replaceable. Doing so puts a lot of strain on the compiler. I ran a few test and benchmarks and the maximum number of fields in scalar-replaced object that I've seen was 59. I think it should be reasonable to set a limit on the number of fields to 512.