Hi Ramana,
On 11/09/18 15:55, Ramana Radhakrishnan wrote:
On Tue, 11 Sep 2018, 14:38 Vlad Lazar, <vlad.la...@arm.com> wrote:
> Hi.
>
> This patch makes the scheduler prefer instructions with higher cost if two
> given instructions are equally good.
> Issuing more restricted instructions first is particularly useful on
> in-order cores because it increases the
> number of dual issue opportunities.
>
> For example, on AArch64, instead of:
>
> add x11, x2, 96
> mov x4, x2
> mov w10, 1
> ldrh w5, [x0]
> ldrh w13, [x0, 2]
> ldrh w9, [x0, 4]
> ldrh w12, [x0, 6]
> b .L759
>
> Generate:
>
> ldrh w5, [x0]
> add x11, x2, 96
> ldrh w13, [x0, 2]
> mov x4, x2
> ldrh w9, [x0, 4]
> mov w10, 1
> ldrh w12, [x0, 6]
> b .L759
>
> Bootstrapped and regtested on aarch64-none-linux-gnu and there are no
> regressions.
> Ok for trunk?
>
This to me feels like the wrong approach as it feels like you are assuming
INSN_COST is latency in some way ? Surely, we shouldn't be introducing
INSN_COST based stuff into the scheduler.
Have you investigated using TARGET_SCHED_ADJUST_COST (IIRC, look for the
right name in the internals documents) and such hooks that come from the
scheduler rather than trying to massage INSN_COST into the target
independent parts of the scheduler ?
In the context of haifa-sched.c, INSN_COST is the latency cost.
It is not the rtx_cost of the insn, as used by combine and others.
So this approach looks reasonable to me (though I haven't done a deep review).
Thanks,
Kyrill
Ramana
>
> Thanks,
> Vlad
>
> gcc/
> Changelog for gcc/Changelog
> 2018-09-11 Vlad Lazar <vlad.la...@arm.com>
>
> * haifa-sched.c (rank_for_schedule): Schedule by INSN_COST.
> (rfs_decision): New scheduling decision.
>
