[PATCH] Keep lattice abstract in the SSA propagator, substitue lattice values at defs

[Richard Guenther]

On Sun, 8 Aug 2010, Paolo Bonzini wrote:

> On 08/08/2010 04:44 AM, Richard Guenther wrote:
> > arithmetic.  But - we can do so if reassociating constants only
> > as in the example above.  Because if (L43b_216 - 1) - 2147483648
> > doesn't overflow then L43b_216 + 2147483647 doesn't either.
> 
> Huh?
> 
> a - 1 - 2147483648 is valid if a >= 1.
>
> a + 2147483647 is valid if a < 1.

Oh, indeed.  Hm.  I guess we have to be more careful with
constant-folding in reassoc ... (and it's one more reason for
me to pick up no-undefined-overflow again ...).

I guess as I have exposed the issue I have to look into it.

Richard.