Hi, I am looking into distribute_notes, one reason why it's complicated is the live range of register noted by REG_DEAD could be both shrunk or extended. When live range shrinks, we need to search backwards to find previous reference and mark it as REG_DEAD (or delete the definition if there is no reference anymore); when live range extends, we need to search forward to see if we can mark later reference as REG_DEAD. Maybe the reason why distribute_notes is so vulnerable is because it guesses how to distribute DEAD note based on other information (elim_ix, i2, i3, etc..), rather than how register's live range changes. For example, PR62151 shows the case in which the REG_DEAD should be discarded, but distribute_notes falsely tries to shrink the live range (even worse, from a wrong point), resulting in wrong instruction deleted.
So I am wondering if I can rely on INSN_LUID checking orders of difference instruction. If it can be done, I can easily differentiate live range shrink and extend. Further question is, if we don't insert new insns, can I use INSN_LUID safely for this purpose? Thanks, bin
