Re: [PATCH] Fix optimization regression in constant folder

[Ian Lance Taylor <iant at google dot com>]

kenner@vlsi1.ultra.nyu.edu (Richard Kenner) writes:

> > 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!

The flags aren't fixed in stone.  In fact, I just introduced them
earlier this year.  So all this tells me is that we need to change the
flags.  I already proposed such a change
(http://gcc.gnu.org/ml/gcc-patches/2007-10/msg00053.html).  Nobody has
yet explained why my proposal wouldn't work.

> 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.

Again, it's a big deal because at the moment most of the gcc
maintainers don't understand the semantics.  After all this discussion
I still barely have a handle on what you want.  You are talking in
vague generalities, and you are unable to give us any actual code.
It's no wonder we remain confused.

Ian