Re: [PATCH PR71734] Add missed check that reference defined inside loop.

[Yuri Rumyantsev <ysrumyan at gmail dot com>]

Richard,

I checked that this move helps.
Does it mean that I've got approval to integrate it to trunk?

2016-08-09 14:33 GMT+03:00 Richard Biener <richard.guenther@gmail.com>:
> On Tue, Aug 9, 2016 at 1:26 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>> Richard,
>>
>> The patch proposed by you does not work properly for
>> g++.dg/vect/pr70729-nest.cc test since the reference for this->S_n has
>> been cached as dependent for outer loop and loop is not vectorized:
>>
>>  g++ -Ofast -fopenmp -mavx2 pr70729-nest.cc -c
>> -fdump-tree-vect-details
>> grep 'LOOP VECTORIZED' pr70729-nest.cc.149t.vect
>> <not found>
>>
>> You missed additional check I added before check on cached dependence.
>
> Ok, but it should get the correctness right?
>
> I suppose that if you move the cache checks inside the else clause it
> would work?
> I'd be ok with that change.
>
> Richard.
>
>> 2016-08-09 13:00 GMT+03:00 Richard Biener <richard.guenther@gmail.com>:
>>> On Tue, Aug 9, 2016 at 11:20 AM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>>>> Yes it is impossible since all basic blocks are handled from outer
>>>> loops to innermost so we can not have the sequence with wrong
>>>> dependence, i.e. we cached that reference is independent (due to
>>>> safelen) but the same reference in outer loop must be evaluated as
>>>> dependent. So we must re-evaluate only dependent references in loops
>>>> having non-zero safelen attribute.
>>>
>>> Hmm.  I don't like depending on this implementation detail.  Does the
>>> attached patch work
>>> which simply avoids any positive/negative caching on safelen affected
>>> refs?  It also makes
>>> the query cheaper by avoiding the dive into child loops.
>>>
>>> Richard.
>>>
>>>> 2016-08-09 11:44 GMT+03:00 Richard Biener <richard.guenther@gmail.com>:
>>>>> On Fri, Aug 5, 2016 at 4:57 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>>>>>> Richard,
>>>>>>
>>>>>> I added additional check before caching dependencies since (1) all
>>>>>> statements in loop are handled in loop postorder order, i.e. form
>>>>>> outer to inner; (2) we can change dependency for reference in subloops
>>>>>> which have non-zero safelen attribute. So I propose to re-evaluate it
>>>>>> in such cases. I don't see why we need to avoid dependence caching for
>>>>>> all loop nests since pragma omp simd is used very rarely.
>>>>>
>>>>> You think it is impossible to construct a testcase which hits the
>>>>> correctness issue?
>>>>> "very rarely" is not a good argument to generate wrong code.
>>>>>
>>>>> Richard.
>>>>>
>>>>>> 2016-08-05 16:50 GMT+03:00 Richard Biener <richard.guenther@gmail.com>:
>>>>>>> On Fri, Aug 5, 2016 at 3:28 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>>>>>>>> Richard,
>>>>>>>>
>>>>>>>> Here is updated patch which implements your proposal - I pass loop
>>>>>>>> instead of stmt to determine either REF is defined inside LOOP nest or
>>>>>>>> not. I checked that for pr70729-nest.cc the reference this->S_n  for
>>>>>>>> statements which are out of innermost loop are  not considered as
>>>>>>>> independent as you pointed out.
>>>>>>>>
>>>>>>>> Regression testing did not show any new failures and both failed tests
>>>>>>>> from libgomp.fortran suite now passed.
>>>>>>>>
>>>>>>>> Is it OK for trunk?
>>>>>>>
>>>>>>> I don't quite understand
>>>>>>>
>>>>>>> +  /* Ignore dependence for loops having greater safelen.  */
>>>>>>> +  if (new_safelen == safelen
>>>>>>> +      && bitmap_bit_p (&ref->dep_loop, LOOP_DEP_BIT (loop->num, stored_p)))
>>>>>>>      return false;
>>>>>>>
>>>>>>> this seems to suggest (correctly I think) that we cannot rely on the caching
>>>>>>> for safelen, neither for optimal results (you seem to address that) but also
>>>>>>> not for correctness (we cache the no-dep result from a safelen run and
>>>>>>> then happily re-use that info for a ref that is not safe for safelen).
>>>>>>>
>>>>>>> It seems to me we need to avoid any caching if we made things independent
>>>>>>> because of safelen and simply not do the dep test afterwards.  this means
>>>>>>> inlining ref_indep_loop_p_1 partly into _2 (not sure if there's a great way
>>>>>>> to do this w/o confusing the control flow).
>>>>>>>
>>>>>>> Richard.
>>>>>>>
>>>>>>>> ChangeLog:
>>>>>>>> 2016-08-05  Yuri Rumyantsev  <ysrumyan@gmail.com>
>>>>>>>>
>>>>>>>> PR tree-optimization/71734
>>>>>>>> * tree-ssa-loop-im.c (ref_indep_loop_p): Add new argument REF_LOOP.
>>>>>>>> (outermost_indep_loop): Pass LOOP argumnet where REF was defined to
>>>>>>>> ref_indep_loop_p.
>>>>>>>> (ref_indep_loop_p_1): Fix commentary.
>>>>>>>> (ref_indep_loop_p_2): Add additional argument REF_LOOP, introduce new
>>>>>>>> variable NEW_SAFELEN which may have new value for SAFELEN, ignore
>>>>>>>> dependencde for loop having greater safelen value, pass REF_LOOP in
>>>>>>>> recursive call.
>>>>>>>> (can_sm_ref_p): Pass LOOP as additional argument to ref_indep_loop_p.
>>>>>>>>
>>>>>>>> 2016-08-03 16:44 GMT+03:00 Richard Biener <richard.guenther@gmail.com>:
>>>>>>>>> On Fri, Jul 29, 2016 at 4:00 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>>>>>>>>>> Hi Richard.
>>>>>>>>>>
>>>>>>>>>> It turned out that the fix proposed by you does not work for liggomp
>>>>>>>>>> tests simd3 and simd4.
>>>>>>>>>> The reason is that we can't change safelen value for references not
>>>>>>>>>> defined inside loop. So I add missed check on it to patch.
>>>>>>>>>> Is it OK for trunk?
>>>>>>>>>
>>>>>>>>> Hmm, I don't like the walk of all subloops in ref_defined_in_loop_p as
>>>>>>>>> that operation can end up being quadratic in the loop depth/width.
>>>>>>>>>
>>>>>>>>> But I also wonder about correctness given that LIM "commons"
>>>>>>>>> references.  So we can have
>>>>>>>>>
>>>>>>>>>   for (;;)
>>>>>>>>>     .. = ref;  (1)
>>>>>>>>>     for (;;) // safelen == 2  (2)
>>>>>>>>>       ... = ref;
>>>>>>>>>
>>>>>>>>> and when looking at the ref at (1) which according to you should not
>>>>>>>>> have safelen applied your function will happily return that ref is defined
>>>>>>>>> in the inner loop.
>>>>>>>>>
>>>>>>>>> So it looks like to be able to apply safelen the caller of ref_indep_loop_p
>>>>>>>>> needs to pass down a ref plus a location (a stmt).  In which case your
>>>>>>>>> function can simply use flow_loop_nested_p (loop, gimple_bb
>>>>>>>>> (stmt)->loop_father);
>>>>>>>>>
>>>>>>>>> Richard.
>>>>>>>>>
>>>>>>>>>> ChangeLog:
>>>>>>>>>> 2016-07-29  Yuri Rumyantsev  <ysrumyan@gmail.com>
>>>>>>>>>>
>>>>>>>>>> PR tree-optimization/71734
>>>>>>>>>> * tree-ssa-loop-im.c (ref_defined_in_loop_p): New function.
>>>>>>>>>> (ref_indep_loop_p_2): Change SAFELEN value for REF defined inside LOOP.
>>>>>>>>>>
>>>>>>>>>> 2016-07-29 13:08 GMT+03:00 Yuri Rumyantsev <ysrumyan@gmail.com>:
>>>>>>>>>>> Sorry H.J.
>>>>>>>>>>>
>>>>>>>>>>> I checked both these tests manually but forgot to pass "-fopenmp" option.
>>>>>>>>>>> I will fix the issue asap.
>>>>>>>>>>>
>>>>>>>>>>> 2016-07-29 0:33 GMT+03:00 H.J. Lu <hjl.tools@gmail.com>:
>>>>>>>>>>>> On Thu, Jul 28, 2016 at 6:49 AM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>>>>>>>>>>>>> Richard,
>>>>>>>>>>>>>
>>>>>>>>>>>>> I prepare a patch which is based on yours. New test is also included.
>>>>>>>>>>>>> Bootstrapping and regression testing did not show any new failures.
>>>>>>>>>>>>> Is it OK for trunk?
>>>>>>>>>>>>>
>>>>>>>>>>>>> Thanks.
>>>>>>>>>>>>> ChangeLog:
>>>>>>>>>>>>> 2016-07-28  Yuri Rumyantsev  <ysrumyan@gmail.com>
>>>>>>>>>>>>>
>>>>>>>>>>>>> PR tree-optimization/71734
>>>>>>>>>>>>> * tree-ssa-loop-im.c (ref_indep_loop_p_1): Pass value of safelen
>>>>>>>>>>>>> attribute instead of REF_LOOP and use it.
>>>>>>>>>>>>> (ref_indep_loop_p_2): Use SAFELEN argument instead of REF_LOOP and
>>>>>>>>>>>>> set it for Loops having non-zero safelen attribute.
>>>>>>>>>>>>> (ref_indep_loop_p): Pass zero as initial value for safelen.
>>>>>>>>>>>>> gcc/testsuite/ChangeLog:
>>>>>>>>>>>>>         * g++.dg/vect/pr70729-nest.cc: New test.
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> Does this cause
>>>>>>>>>>>>
>>>>>>>>>>>> FAIL: libgomp.fortran/pr71734-1.f90   -O3 -fomit-frame-pointer
>>>>>>>>>>>> -funroll-loops -fpeel-loops -ftracer -finline-functions  execution
>>>>>>>>>>>> test
>>>>>>>>>>>> FAIL: libgomp.fortran/pr71734-1.f90   -O3 -g  execution test
>>>>>>>>>>>> FAIL: libgomp.fortran/pr71734-2.f90   -O3 -fomit-frame-pointer
>>>>>>>>>>>> -funroll-loops -fpeel-loops -ftracer -finline-functions  execution
>>>>>>>>>>>> test
>>>>>>>>>>>> FAIL: libgomp.fortran/pr71734-2.f90   -O3 -g  execution test
>>>>>>>>>>>>
>>>>>>>>>>>> on AVX machines and
>>>>>>>>>>>>
>>>>>>>>>>>> FAIL: libgomp.fortran/simd3.f90   -O3 -fomit-frame-pointer
>>>>>>>>>>>> -funroll-loops -fpeel-loops -ftracer -finline-functions  execution
>>>>>>>>>>>> test
>>>>>>>>>>>> FAIL: libgomp.fortran/simd3.f90   -O3 -g  execution test
>>>>>>>>>>>> FAIL: libgomp.fortran/simd4.f90   -O3 -fomit-frame-pointer
>>>>>>>>>>>> -funroll-loops -fpeel-loops -ftracer -finline-functions  execution
>>>>>>>>>>>> test
>>>>>>>>>>>> FAIL: libgomp.fortran/simd4.f90   -O3 -g  execution test
>>>>>>>>>>>>
>>>>>>>>>>>> on non-AVX machines?
>>>>>>>>>>>>
>>>>>>>>>>>> --
>>>>>>>>>>>> H.J.