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Re: [PATCH v6 3/3] PR80791 Consider doloop cmp use in ivopts

Hi Bin

on 2019/8/23 上午10:19, Bin.Cheng wrote:
> On Thu, Aug 22, 2019 at 3:09 PM Kewen.Lin <> wrote:
>> Hi Bin,
>> on 2019/8/22 下午1:46, Bin.Cheng wrote:
>>> On Thu, Aug 22, 2019 at 11:18 AM Kewen.Lin <> wrote:
>>>> Hi Bin,
>>>> Thanks for your time!
>>>> on 2019/8/21 下午8:32, Bin.Cheng wrote:
>>>>> On Wed, Aug 14, 2019 at 3:23 PM Kewen.Lin <> wrote:
>>>>>> Hi!
>>>>>> Comparing to the previous versions of implementation mainly based on the
>>>>>> existing IV cands but zeroing the related group/use cost, this new one is based
>>>>>> on Richard and Segher's suggestion introducing one doloop dedicated IV cand.
>>>>>> Some key points are listed below:
>>>>>>   1) New field doloop_p in struct iv_cand to indicate doloop dedicated IV cand.
>>>>>>   2) Special name "doloop" assigned.
>>>>>>   3) Doloop IV cand with form (niter+1, +, -1)
>>>>>>   4) For doloop IV cand, no extra one cost like BIV, assign zero cost for step.
>>>>>>   5) Support may_be_zero (regressed PR is in this case), the base of doloop IV
>>>>>>      can be COND_EXPR, add handlings in cand_value_at and may_eliminate_iv.
>>>>>>   6) Add more expr support in force_expr_to_var_cost for reasonable cost
>>>>>>      calculation on the IV base with may_be_zero (like COND_EXPR).
>>>>>>   7) Set zero cost when using doloop IV cand for doloop use.
>>>>>>   8) Add three hooks (should we merge _generic and _address?).
>>>>>>     *) have_count_reg_decr_p, is to indicate the target has special hardware
>>>>>>        count register, we shouldn't consider the impact of doloop IV when
>>>>>>        calculating register pressures.
>>>>>>     *) doloop_cost_for_generic, is the extra cost when using doloop IV cand for
>>>>>>        generic type IV use.
>>>>>>     *) doloop_cost_for_address, is the extra cost when using doloop IV cand for
>>>>>>        address type IV use.

>> The new patch addressing the comments is attached.
>> Could you please have a look again?  Thanks in advance!
> Thanks for working on this.  A bit more nit-pickings.
> -    add_candidate_1 (data, base, step, important,
> -                    IP_NORMAL, use, NULL, orig_iv);
> -  if (ip_end_pos (data->current_loop)
> +    add_candidate_1 (data, base, step, important, IP_NORMAL, use, NULL, doloop,
> +                    orig_iv);
> +  if (!doloop && ip_end_pos (data->current_loop)
> Could you add some comments elaborating why ip_end_pos candidate
> shouldn't be added for doloop case?  Because the increment position is
> wrong.
> Also if you make doloop the last default parameter of add_candidate_1,
> you can save more unnecessary changes to calls to add_candidate?
> -    cost = get_computation_cost (data, use, cand, false,
> -                                &inv_vars, NULL, &inv_expr);
> +    {
> +      cost = get_computation_cost (data, use, cand, false, &inv_vars, NULL,
> +                                  &inv_expr);
> +      if (cand->doloop_p)
> +       cost += targetm.doloop_cost_for_generic;
> +    }
> This adjustment
>    cost = get_computation_cost (data, use, cand, true,
>                                &inv_vars, &can_autoinc, &inv_expr);
> +  if (cand->doloop_p)
> +    cost += targetm.doloop_cost_for_address;
> +
> and this adjustment can be moved into get_computation_cost where all
> cost adjustments are done.
> +      /* For doloop candidate/use pair, adjust to zero cost.  */
> +      if (group->doloop_p && cand->doloop_p)
> +       cost = no_cost;
> Note above code handles comparing against zero case and decreases the
> cost by one (which prefers the same kind candidate as doloop one),
> it's very possible to have -1 cost for doloop cand here.  how about
> just set to no_cost if it's positive?  Your call.
> +/* For the targets which support doloop, to predict whether later RTL doloop
> +   transformation will perform on this loop, further detect the doloop use and
> +   mark the flag doloop_use_p if predicted.  */
> +
> +void
> +predict_and_process_doloop (struct ivopts_data *data)
> A better name here? Sorry I don't have another candidate in mind...
> +  data->doloop_use_p = false;
> This can be moved to the beginning of above
> 'predict_and_process_doloop' function.
> Lastly, could you please add some brief description/comment about
> doloop handling as a subsection in the file head comment?
> Otherwise, the ivopt changes look good to me.
> Thanks,
> bin

Thanks for your prompt reply!  I've updated the code as your comments,
the updated version is attached.  Looking forward to your review again.




2019-08-23  Kewen Lin  <>

	PR middle-end/80791
	* config/rs6000/rs6000.c (TARGET_HAVE_COUNT_REG_DECR_P): New macro.
	* target.def (have_count_reg_decr_p): New hook.
	(doloop_cost_for_generic): Likewise.
	(doloop_cost_for_address): Likewise.
	* doc/ (TARGET_HAVE_COUNT_REG_DECR_P): Likewise.
	* doc/tm.texi: Regenerate.
	* tree-ssa-loop-ivopts.c (comp_cost::operator+=): Consider infinite cost
	(record_group): Init doloop_p.
	(add_candidate_1): Add optional argument doloop, change the handlings
	(add_candidate): Likewise.
	(generic_predict_doloop_p): Update attribute.
	(force_expr_to_var_cost): Add costing for expressions COND_EXPR/LT_EXPR/
	(get_computation_cost): Update for doloop IV cand extra cost.	
	(determine_group_iv_cost_cond): Update for doloop IV cand.
	(determine_iv_cost): Likewise.
	(ivopts_estimate_reg_pressure): Likewise.
	(may_eliminate_iv): Update handlings for doloop IV cand.
	(add_iv_candidate_for_doloop): New function.
	(find_iv_candidates): Call function add_iv_candidate_for_doloop.
	(iv_ca_set_no_cp): Update for doloop IV cand.
	(iv_ca_set_cp): Likewise.
	(iv_ca_dump): Dump register cost.
	(find_doloop_use): New function.
	(analyze_and_mark_doloop_use): Likewise.
	(tree_ssa_iv_optimize_loop): Call function analyze_and_mark_doloop_use.


2019-08-23  Kewen Lin  <>

	PR middle-end/80791
	* gcc.dg/tree-ssa/ivopts-3.c: Adjust for doloop change.
	* gcc.dg/tree-ssa/ivopts-lt.c: Likewise.
	* gcc.dg/tree-ssa/pr32044.c: Likewise.

Attachment: doloop_dedicated_iv3.diff
Description: Text document

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