Ping?
On Fri, Apr 27, 2012 at 4:42 PM, Igor Zamyatin <izamya...@gmail.com> wrote:
> On Wed, Apr 25, 2012 at 6:41 PM, Richard Guenther
> <richard.guent...@gmail.com> wrote:
>> On Wed, Apr 25, 2012 at 4:32 PM, Igor Zamyatin <izamya...@gmail.com> wrote:
>>> On Wed, Apr 25, 2012 at 1:14 PM, Richard Guenther
>>> <richard.guent...@gmail.com> wrote:
>>>> On Wed, Apr 25, 2012 at 10:56 AM, Igor Zamyatin <izamya...@gmail.com>
>>>> wrote:
>>>>> Hi all!
>>>>>
>>>>> I'd like to post for review the patch which makes some costs adjusting
>>>>> in get_computation_cost_at routine in ivopts part.
>>>>> As mentioned in the PR changes also fix the bwaves regression from PR
>>>>> 52272.
>>>>> Also changes introduce no degradations on spec2000/2006 and
>>>>> EEMBC1.1/2.0(this was measured on Atom) on x86
>>>>>
>>>>>
>>>>> Bootstrapped and regtested on x86. Ok to commit?
>>>>
>>>> I can't make sense of the patch and the comment does not help.
>>>>
>>>> + diff_cost = cost.cost;
>>>> cost.cost /= avg_loop_niter (data->current_loop);
>>>> + add_cost_val = add_cost (TYPE_MODE (ctype), data->speed);
>>>> + /* Do cost correction if address cost is small enough
>>>> + and difference cost is high enough. */
>>>> + if (address_p && diff_cost > add_cost_val
>>>> + && get_address_cost (symbol_present, var_present,
>>>> + offset, ratio, cstepi,
>>>> + TYPE_MODE (TREE_TYPE (utype)),
>>>> + TYPE_ADDR_SPACE (TREE_TYPE (utype)),
>>>> + speed, stmt_is_after_inc,
>>>> + can_autoinc).cost <= add_cost_val)
>>>> + cost.cost += add_cost_val;
>>>>
>>>> Please explain more thoroughly. It also would seem to be better to add
>>>> an extra case, as later code does
>>>
>>> For example for such code
>>>
>>> for (j=0; j<M;j++) {
>>> for (i=0; i<N; i++)
>>> sum += ptr->a[j][i] * ptr->c[k][i];
>>> }
>>> we currently have following gimple on x86 target (I provided a piece
>>> of all phase output):
>>>
>>> # ivtmp.13_30 = PHI <ivtmp.13_31(3), ivtmp.13_33(7)>
>>> D.1748_34 = (void *) ivtmp.13_30;
>>> D.1722_7 = MEM[base: D.1748_34, offset: 0B];
>>> D.1750_36 = ivtmp.27_28;
>>> D.1751_37 = D.1750_36 + ivtmp.13_30; <-- we got
>>> non-invariant add which is not taken into account currently in cost
>>> model
>>> D.1752_38 = (void *) D.1751_37;
>>> D.1753_39 = (sizetype) k_8(D);
>>> D.1754_40 = D.1753_39 * 800;
>>> D.1723_9 = MEM[base: D.1752_38, index: D.1754_40, offset: 16000B];
>>> ...
>>>
>>> With proposed fix we produce:
>>>
>>> # ivtmp.14_30 = PHI <ivtmp.14_31(3), 0(7)>
>>> D.1749_34 = (struct S *) ivtmp.25_28;
>>> D.1722_7 = MEM[base: D.1749_34, index: ivtmp.14_30, offset: 0B];
>>> D.1750_35 = (sizetype) k_8(D);
>>> D.1751_36 = D.1750_35 * 800;
>>> D.1752_37 = ptr_6(D) + D.1751_36;
>>> D.1723_9 = MEM[base: D.1752_37, index: ivtmp.14_30, offset:
>>> 16000B];
>>>
>>> which is more effective on platforms where address cost is cheaper
>>> than cost of addition operation. That's basically what this adjustment
>>> is for.
>>
>> If we generally miss to account for the add then why is the adjustment
>> conditional on diff_cost > add_cost and address_cost <= add_cost?
>>
>> Is this a new heuristic or a fix for not accurately computing the cost for
>> the
>> stmts we generate?
>
> I'd say this is closer to heuristic since diff_cost > add_cost is an
> attempt to catch the case with non-invariant add produced by pointer
> difference and address_cost <=add_cost leaves the cases with cheap
> address operations
>
>>
>> Richard.
>>
>>> So comment in the source code now looks as follows
>>>
>>> /* Do cost correction when address difference produces
>>> additional non-invariant add operation which is less
>>> profitable if address cost is cheaper than cost of add. */
>>>
>>>>
>>>> /* Now the computation is in shape symbol + var1 + const + ratio * var2.
>>>> (symbol/var1/const parts may be omitted). If we are looking for an
>>>> address, find the cost of addressing this. */
>>>> if (address_p)
>>>> return add_costs (cost,
>>>> get_address_cost (symbol_present, var_present,
>>>> offset, ratio, cstepi,
>>>> TYPE_MODE (TREE_TYPE (utype)),
>>>> TYPE_ADDR_SPACE (TREE_TYPE (utype)),
>>>> speed, stmt_is_after_inc,
>>>> can_autoinc));
>>>>
>>>> thus refactoring the code a bit would make it possible to CSE the
>>>> get_address_cost
>>>> call and eventually make it clearer what the code does.
>>>
>>> 'offset' could be changed beetween two calls of get_address_cost so
>>> such refactoring looks useless.
>>>
>>> New patch (only the comment was changed) attached. Changelog was
>>> changed as well.
>>>
>>>>
>>>> Richard.
>>>>
>>>
>>> Changelog:
>>>
>>> 2012-04-26 Yuri Rumyantsev <yuri.rumyant...@intel.com>
>>>
>>> * tree-ssa-loop-ivopts.c (get_computation_cost_at): Adjust
>>> cost model when address difference produces additional
>>> non-invariant add operation which is less profitable if
>>> address cost is cheaper than cost of add.
>>>
>>> Thanks,
>>> Igor
