------- Comment #17 from amylaar at gcc dot gnu dot org 2006-10-31 14:34 ------- (In reply to comment #4) > It is curious that life2 is running immediately before sched, instead of > immediately after combine. If we ran it immediately after combine, we could > get rid of the REG_DEAD/REG_UNUSED support in distribute_notes, which is > probably the most complicated, and most buggy, part of combine. This would > also speed up the compiler a little bit.
The combiner itself relies on REG_DEAD notes to find out what it can combine. If you leave an invalid REG_DEAD note, it can lead to wrong code being emitted. If you don't leave in valid REG_DEAD notes in their proper place, multi-step instruction combinations will stop working - and with the three insn limit on any single combination, this is likely to stop quite a lot of combinations. Most combiner bridge patterns will become useless. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27883
