[RFC] Tightening up the type system

[Andrew Haley]

Diego Novillo writes:
 > 
 > 
 > My question to the FE folks is: what are the right semantics for
 > checking MODIFY_EXPR?  Is compatible_types_p too strict?  Should we have
 > had a cast operation in the above assignment?
 > 
 > Not having the right types is increasingly getting in the way of the
 > optimizers because we use compatible_types_p quite often to validate
 > propagation opportunities.

It's an interesting view.  I'm pretty sure that we violate this is the
Java FE in a few places, but perhaps we shouldn't.  The trouble is
that the GENERIC type system has never been so well-defined.

I'm sure that enforcing this would break things and it would take some
time to find and fix them all. 

Andrew.