Alex Coplan <alex.cop...@arm.com> writes:
> While working on PR113089, I realised we where missing code to re-parent
> trailing nondebug uses of the base register in the case of cancelling
> writeback in the load/store pair pass. This patch fixes that.
>
> Bootstrapped/regtested as a series on aarch64-linux-gnu (with/without
> the pass enabled), OK for trunk?
>
> Thanks,
> Alex
>
> gcc/ChangeLog:
>
> PR target/113089
> * config/aarch64/aarch64-ldp-fusion.cc (ldp_bb_info::fuse_pair):
> Update trailing nondebug uses of the base register in the case
> of cancelling writeback.
OK, thanks. I suppose in future it would be good to have a way of
stitching together the use lists of two consecutive defs, since that
should be possible in constant time. But that's just a possible future
enhancement. The update as it stands should still be linear, since all
updated uses would come before the next writeback candidate involving
the same base register.
Richard
> ---
> gcc/config/aarch64/aarch64-ldp-fusion.cc | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/gcc/config/aarch64/aarch64-ldp-fusion.cc
> b/gcc/config/aarch64/aarch64-ldp-fusion.cc
> index 70b75c668ce..4d7fd72c6b1 100644
> --- a/gcc/config/aarch64/aarch64-ldp-fusion.cc
> +++ b/gcc/config/aarch64/aarch64-ldp-fusion.cc
> @@ -1693,6 +1693,30 @@ ldp_bb_info::fuse_pair (bool load_p,
>
> if (trailing_add)
> changes.safe_push (make_delete (trailing_add));
> + else if ((writeback & 2) && !writeback_effect)
> + {
> + // The second insn initially had writeback but now the pair does not,
> + // need to update any nondebug uses of the base register def in the
> + // second insn. We'll take care of debug uses later.
> + auto def = find_access (insns[1]->defs (), base_regno);
> + gcc_assert (def);
> + auto set = dyn_cast<set_info *> (def);
> + if (set && set->has_nondebug_uses ())
> + {
> + auto orig_use = find_access (insns[0]->uses (), base_regno);
> + for (auto use : set->nondebug_insn_uses ())
> + {
> + auto change = make_change (use->insn ());
> + change->new_uses = check_remove_regno_access (attempt,
> + change->new_uses,
> + base_regno);
> + change->new_uses = insert_access (attempt,
> + orig_use,
> + change->new_uses);
> + changes.safe_push (change);
> + }
> + }
> + }
>
> auto is_changing = insn_is_changing (changes);
> for (unsigned i = 0; i < changes.length (); i++)
