df.c data reprezentation

[Jan Hubicka]

Hi,
Just note about the data reprezentation.  Unlike our previous dataflow analyzers
(REG_DEAD/UNUSED notes+loglinks), we don't use RTL to reprezent the dataflow here.

Do you consider that as supperrior?  Main advantage of RTL based reprezentation is the
fact that you can easilly attach the information to each insn and see it reprezented
in the dumps?

It would actually mean to change REF structure to RTX form and use expr_list for links.
Insn info can use the existing loglink field with one new for the oposite chain.

What do you think?

Honza