https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106746
--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Alex, please correct me if I'm wrong, but I think the scheduling DEBUG_INSN
decision was that DEBUG_INSNs are somehow taken into account during scheduling,
not completely ignored, so that they actually move together with scheduling
changes.
I know H.J. has posted a patch to ignore for scheduling purposes everything
inside of CONCAT{,N}, but the scheduler itself doesn't specifically check for
those 2 rtxes anywhere, so I don't find anything special on them. And as has
been tried, ignoring DEBUG_INSNs for all scheduler decisions regresses a lot
(not unsuprisingly), they should be scheduled after insns which produce/store
what they depend on and before later insns that modify the registers/memroy
used in them if possible (or reset if that would affect
how non-DEBUG_INSNs are scheduled relative to each other). Though, I think
DEBUG_INSNs should be treated as needing no computing resources, with 0
latencies.
