[dataflow] partial register handling

[Roman Zippel]

Hi,

On Fri, 11 May 2007, Kenneth Zadeck wrote:

> There was a debate several months ago on this issue: how much should the
> df scanner be a theorem prover with respect to how many bits survive an
> operation.
> For instance, I could easily add to your list, anding and oring
> operations which also preserve bits. 

I think that's a different problem, as I don't want to know which bits 
exactly survive. It's about the information that something survived. If we 
can't or don't want to prove what survives we can't eliminate previous 
operations.
The problem here is that scanner IMO incorrectly thinks that nothing 
survives (by not setting the partial bit).

bye, Roman