Performance regression

[Jim Wilson]

>Just to be clear, which new optimizations did you have in mind?

I don't have any specific optimizations in mind, I just know that we will
need new optimizations to replace what we lost when LOAD_EXTEND_OP semantics
changed.  Actually, we may want to eliminate LOAD_EXTEND_OP someday, since
if we had explicit optimization support for sign/zero-extend operators, then
we wouldn't need most of what LOAD_EXTEND_OP does.

Jim