re PR debug/48866 (gcc hangs when -g is set)

re PR debug/48866 (gcc hangs when -g is set)

PR debug/48866
* df.h (enum debug_temp_where): New.
(dead_debug_init, dead_debug_finish) Declare.
(dead_debug_add, dead_debug_insert_temp): Declare.
(struct dead_debug_use, struct dead_debug): Moved from...
* df-problems.c: ... here.
(df_set_unused_notes_for_mw): Bind debug uses of unused regno
to a debug temp.
(df_create_unused_note): Likewise.
(df_set_dead_notes_for_mw): Move comment where it belongs.
(dead_debug_init): Export.
(dead_debug_reset_uses): New, factored out of...
(dead_debug_finish): ...this.  Export.
(dead_debug_reset): Remove.
(dead_debug_add): Export.
(dead_debug_insert_before): Rename to...
(dead_debug_insert_temp): ... this.  Add where argument.  Export.
Locate stored value for BEFORE_WITH_VALUE.  Avoid repeat inserts.
Return insertion count.
(df_note_bb_compute): Adjust.
* dce.c (word_dce_process_block): Adjust dead debug uses.
(dce_process_block): Likewise.

From-SVN: r186422