Re: RFA: New pass to delete unexecutable paths in the CFG

[Paolo Bonzini <bonzini at gnu dot org>]

On 11/08/2011 08:29 PM, Jeff Law wrote:
> > Just to understand, what does this do with your optimization?
> >
> > void f(void *p) {
> >  if (p) {
> >    puts("sell_soul_to_devil"); puts("post_reload_rewrite"); }
> >
> >  *p = 2; }
> >
> > ... f(NULL);
> >
> > Does the program sell its soul to the devil before crashing?
>
> If "f" is not inlined into its caller, then there's nothing for the
> new pass to do.  There's no explicit NULL dereference and there's no
> assignments to "p", so there's no PHI at the merge point for P.

But is that just a limitation of the representation?  With assertions as 
in VRP you'd have

   if (p_1) goto BB1 else goto BB2
BB1: ... goto BB3;
BB2: p_2 = assert(p_1, p_1 == 0); goto BB3;

   p_3 = phi (p_1<BB1>, p_2<BB2>);
   *p_3 = 2;

What would happen then?

Paolo