encode order of operands into interface? guarantee decode_table.c order?

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on May 07, 2011 20:58:27_

Today DR's IR lets you iterate over the operands and query the type of each
one. But in Dr. Memory I end up writing code that knows the order of the
operands, because I wrote the decoder and I can look in decode_table.c and
see how the operands are laid out. E.g., I know src1 can't reference
memory, or that src0 is the immediate, etc., and I can thus write more
efficient (though less general) code. Should we support this and guarantee
we won't go changing the order?

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=451_