On Thu, May 11, 2017 at 11:39 AM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Tue, Apr 18, 2017 at 12:53 PM, Bin Cheng <bin.ch...@arm.com> wrote:
>> Hi,
>> Currently IVOPTs shares the same register pressure computation with RTL loop
>> invariant pass,
>> which doesn't work very well. This patch introduces specific interface for
>> IVOPTs.
>> The general idea is described in the cover message as below:
>> C) Current implementation shares the same register pressure computation
>> with RTL loop
>> inv pass. It has difficulty in handling (especially large) loop nest,
>> and quite
>> often generating too many candidates (especially for outer loops).
>> This change
>> introduces new register pressure computation. The brief idea is to
>> differentiate
>> (hot) innermost loop and outer loop. for (possibly hot) inner most,
>> more registers
>> are allowed as long as the register pressure is within the range of
>> number of target
>> available registers.
>> It can also help to restrict number of candidates for outer loop.
>> Is it OK?
>
> +/* Determine if current loop is the innermost loop and maybe hot. */
> +
> +static void
> +determine_hot_innermost_loop (struct ivopts_data *data)
> +{
> + data->hot_innermost_loop_p = true;
> + if (!data->speed)
> + return;
>
> err, so when not optimizing for speed we assume all loops (even not innermost)
> are hot and innermost?!
>
> + HOST_WIDE_INT niter = avg_loop_niter (loop);
> + if (niter < PARAM_VALUE (PARAM_AVG_LOOP_NITER)
> + || loop_constraint_set_p (loop, LOOP_C_PROLOG)
> + || loop_constraint_set_p (loop, LOOP_C_EPILOG)
> + || loop_constraint_set_p (loop, LOOP_C_VERSION))
> + data->hot_innermost_loop_p = false;
>
> this needs adjustment for the constraint patch removal. Also looking at niter
> of the loop in question insn't a good metric for hotness. data->speed is the
> best guess you get I think (optimize_loop_for_speed_p).
Yes, I also found this is inefficient finding the targeting loops. I
will update and benchmark new patch discarding all *hot innermost*
part. It can always be improved in future.
Thanks,
bin
>
> data->speed = optimize_loop_for_speed_p (loop);
> + determine_hot_innermost_loop (data);
>
> data->hot_innermost_loop_p = determine_hot_innermost_loop (data);
>
> would be more consistent here.
>
> Thanks,
> Richard.
>
>> Thanks,
>> bin
>> 2017-04-11 Bin Cheng <bin.ch...@arm.com>
>>
>> * tree-ssa-loop-ivopts.c (struct ivopts_data): New field.
>> (ivopts_estimate_reg_pressure): New reg_pressure model function.
>> (ivopts_global_cost_for_size): Delete.
>> (determine_set_costs, iv_ca_recount_cost): Call new model function
>> ivopts_estimate_reg_pressure.
>> (determine_hot_innermost_loop): New.
>> (tree_ssa_iv_optimize_loop): Call above function.
