regcprop and REG_DEAD

[Eric Botcazou]

> A later pass (machdep) relies on the notes, so the fact that the actual
> register liveness no longer matches what the REG_DEAD notes imply seems to
> be a problem.

Again, if a pass consumes these notes, it must df_note_add_problem() on entry.
For machine_reorg, this is too late because the CFG has been destroyed so it 
very likely needs to use a trick akin to that of the generic reorg pass in 
rest_of_pass_free_cfg.

-- 
Eric Botcazou