[dataflow] PATCH removal of more of flow.c.

[Kenneth Zadeck]

Joern RENNECKE wrote:
> Joern Rennecke wrote:
>
>>  I suppose one way to reduce the cost of RU generally would be to
>> find first scan
>> the insns backwards to quickly get rid of all the uses that have a
>> dominating
>> definition in the same extended basic block.
>
> P.S.: I see now that you can build use-def and def-use chains by
> solving RD;
> that should be perfectly adequate for SH -mrelax.
>
I was going to suggest this.
> I'm a bit puzzled now why you need to do RU computation in the first
> place; I see that
> RU only considers definitions as separating, while RD considers any
> kill of a register,
> but that is not really intrisically tied to the direction in the
> control flow you follow;
> you could do the same bitset computations that RD does, but only
> consider redefinitions
I will check this, the kill sets should be the same for the two
problems.  However it could be that ru rotted since it is only
marginally used.

> as impeding propagation of the original definition, in order to build
> the same chains that
> can build with RU.
We need it because I have not, in my copious free time, dived into the
dependence generation code for the schedulers to see what it is using it
for, in addition to the use-def and def-use chains.