DU-chains Vs UD-chains

[Daniel Berlin]

On Tue, Apr 15, 2008 at 10:59 AM, Fran Baena <franbaena@gmail.com> wrote:
> Hi all,
>
>  i'm currently studing alias analysis, and i have some questions, for
>  instance,  when are the du/ud-chains calculated?

ud chains are implicit in SSA form, since each use only has one
reaching definiiton.
du chains are calculated after SSA by the operand scanner.

> Before translating to
>  SSA form?
Nope.

>  If i'm not wrong the def-use chain connects a definition of a variable
>  to all the uses it may flow to, and the use-def chain connects a use
>  to all the definitions that may flow to it. But, what chain is better
>  for data-flow analysis?

one is useful for forward dataflow, the other is useful for backwards dataflow.

>  Maybe the answer is both?
Yes.

>
>  Thanks in advance
>
>  Fran
>