Re: [PATCH] Fix optimization regression in constant folder

[kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)]

> But the rest of us don't understand the semantics of sizetypes.  That
> is why we are trying to pin it down in terms of other flags.  We
> understand what those other flags mean.

The problem is that it's becoming clearer and clearer that the semantics of
sizetypes CAN'T be expressed in terms of those other flags!

One thing to remember is that the vast majority of operations in sizetypes
aren't generated by the front end, but instead by the middle end itself in
stor-layout.c!  So it's primarily optimizing its own operations and
therefore can do so in a consistent manner.

Essentially, what we have to do when we see a transformation that might 
potentially be applied to sizetypes is to rely on our understanding of
the semantics of those operations to see whether or not that transformation
is safe or not.

That set of decisions may or may not corespond to some other set of flags
that we're using for other (unrelated) types.  I don't see it as a big deal
if it doesn't.