re PR debug/54551 (DF resets some DEBUG_INSNs unnecessarily)

re PR debug/54551 (DF resets some DEBUG_INSNs unnecessarily)

PR debug/54551
PR debug/54693
* valtrack.c (dead_debug_global_find): Accept NULL dtemp.
(dead_debug_global_insert): Return new entry.
(dead_debug_global_replace_temp): Return early if REG is no
longer in place, or if dtemp was already substituted.
(dead_debug_promote_uses): Insert for all defs and replace all
debug uses at once.
(dead_debug_local_finish): Release used after promotion.
(dead_debug_insert_temp): Stop if dtemp is NULL.

From-SVN: r192959