[Bug debug/54551] DF resets some DEBUG_INSNs unnecessarily

[aoliva at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54551

--- Comment #1 from Alexandre Oliva <aoliva at gcc dot gnu.org> 2012-09-11 21:20:11 UTC ---
I guess we have to somehow local all death points of the pseudo in paths
towards the debug use, and insert debug insns binding the same debug temp to
the pseudo before all of the death points, then replace the debug use with a
use of the debug temp.  I'm not sure how well this fits in the general
structure of the DF machinery.  Presumably we just need to look up a table of
(lists of?) debug temps as we reach death points.