[tree-ssa] CCP inefficiencies

[Daniel Berlin]

On Fri, 14 Feb 2003, Daniel Berlin wrote:

>
>
> On Fri, 14 Feb 2003, Diego Novillo wrote:
>
> > On Thu, 2003-02-13 at 11:42, Diego Novillo wrote:
> > > On Thu, 2003-02-13 at 11:38, law@redhat.com wrote:
> > >
> > > > Rather than "fixing" fold, we introduce a new, simpler fold_nondestructive
> > > > or whatever.  The number of cases we care about are actually a small subset
> > > > of the cases fold currently handles.
> > > >
> > > OK.  I guess that we only need something along the lines of what Dan
> > > suggested: 'is this expression going to be folded into a constant?'
> > >
> > On second thought, what I said above is completely wrong.  Knowing that
> > the expression is constant is not enough, we *really* need to fold it to
> > compute and return its lattice value from tree-ssa-ccp.c:evaluate_stmt.
>
> I was only talking about replacement, not about evaluation.
> For replacement, an expression can't become constant unless you've
> replaced at least one variable with a constant.
> For evaluation, you can't do it without copying.

At least, i *think* i was only talking about replacement.
It's almost 4am, so if i wake up and write something completely different,
...

>