Bug 14562 : copyrename & PRE

[Daniel Berlin]

> >
> > It probably wouldn't take long for you to see what wrong. Either its
> > something I did about PARM_DECLs, or an assumption PRE is making, Im not
> > sure which.
>
> I'll check it out
>

It looks like we have two occurrences of the expression with copyrename,
and one without it.

 EUSE (k_29 * 4) [class:1 phiop:0 bb:1 ]
 EUSE (k_29 * 4) [class:2 phiop:0 bb:1 ]
 EUSE () [class:-1 phiop:1 bb:6 ]
 EUSE () [class:-1 phiop:1 bb:5 ]

without copyrename:

 EUSE (T.1_29 * 4) [class:2 phiop:0 bb:1 ]
 EUSE () [class:-1 phiop:1 bb:4 ]
 EUSE () [class:-1 phiop:1 bb:3 ]


PRE is not value based (right now, i'm working on a GVN-PRE algorithm), so
this is why it picks it up when you have k, but not T (because in one case
you have one k * 4 expression, and one t * 4 expression, and in the other
case you have two k * 4 expressions)

The results of PRE look fine given the code in both cases (in one case,
the expression we are looking at is modified in between the phi and the
use, and in the other case, it isn't, because we are picking up the extra
expression, and that's the one getting optimized).

Do you see something actually wrong with the code PRE is producing?