DU-chains Vs UD-chains

[Fran Baena]

Hi all,

i'm currently studing alias analysis, and i have some questions, for
instance,  when are the du/ud-chains calculated? Before translating to
SSA form?
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?
Maybe the answer is both?

Thanks in advance

Fran