Re: [PATCH 1/2] vect: Add costing_for_scalar parameter to init_cost hook

["Kewen.Lin" <linkw@linux.ibm.com>]

Hi Richard,

on 2021/5/10 下午10:08, Richard Sandiford wrote:
> "Kewen.Lin via Gcc-patches" <gcc-patches@gcc.gnu.org> writes:
>> on 2021/5/7 下午5:43, Richard Biener wrote:
>>> On Fri, May 7, 2021 at 5:30 AM Kewen.Lin via Gcc-patches
>>> <gcc-patches@gcc.gnu.org> wrote:
>>>>
>>>> Hi,
>>>>
>>>> When I was investigating density_test heuristics, I noticed that
>>>> the current rs6000_density_test could be used for single scalar
>>>> iteration cost calculation, through the call trace:
>>>>   vect_compute_single_scalar_iteration_cost
>>>>     -> rs6000_finish_cost
>>>>          -> rs6000_density_test
>>>>
>>>> It looks unexpected as its desriptive function comments and Bill
>>>> helped to confirm this needs to be fixed (thanks!).
>>>>
>>>> So this patch is to check the passed data, if it's the same as
>>>> the one in loop_vinfo, it indicates it's working on vector version
>>>> cost calculation, otherwise just early return.
>>>>
>>>> Bootstrapped/regtested on powerpc64le-linux-gnu P9.
>>>>
>>>> Nothing remarkable was observed with SPEC2017 Power9 full run.
>>>>
>>>> Is it ok for trunk?
>>>
>>> +  /* Only care about cost of vector version, so exclude scalar
>>> version here.  */
>>> +  if (LOOP_VINFO_TARGET_COST_DATA (loop_vinfo) != (void *) data)
>>> +    return;
>>>
>>> Hmm, looks like a quite "random" test to me.  What about adding a
>>> parameter to finish_cost () (or init_cost?) indicating the cost kind?
>>>
>>
>> I originally wanted to change the hook interface, but noticed that
>> the finish_cost in function vect_estimate_min_profitable_iters is
>> the only invocation with LOOP_VINFO_TARGET_COST_DATA (loop_vinfo),
>> it looks enough to differentiate the scalar version costing or
>> vector version costing for loop.  Do you mean this observation/
>> assumption easy to be broken sometime later?
>>
>> The attached patch to add one new parameter to indicate the
>> costing kind explicitly as you suggested.
>>
>> Does it look better?
>>
>> gcc/ChangeLog:
>>
>> 	* doc/tm.texi: Regenerated.
>> 	* target.def (init_cost): Add new parameter costing_for_scalar.
>> 	* targhooks.c (default_init_cost): Adjust for new parameter.
>> 	* targhooks.h (default_init_cost): Likewise.
>> 	* tree-vect-loop.c (_loop_vec_info::_loop_vec_info): Likewise.
>> 	(vect_compute_single_scalar_iteration_cost): Likewise.
>> 	(vect_analyze_loop_2): Likewise.
>> 	* tree-vect-slp.c (_bb_vec_info::_bb_vec_info): Likewise.
>> 	(vect_bb_vectorization_profitable_p): Likewise.
>> 	* tree-vectorizer.h (init_cost): Likewise.
>> 	* config/aarch64/aarch64.c (aarch64_init_cost): Likewise.
>> 	* config/i386/i386.c (ix86_init_cost): Likewise.
>> 	* config/rs6000/rs6000.c (rs6000_init_cost): Likewise.  
> 
> Just wanted to say thanks for doing this.  I hit the same problem
> when doing the Neoverse V1 tuning near the end of stage 4.  Due to
> the extreme lateness of the changes, I couldn't reasonably ask for
> target-independent help at that time, but this patch will make
> things simpler for AArch64. :-)
> 


Glad to see that rs6000 port isn't the only port requesting this.  :-)
Thanks for the information!
BR,
Kewen