On Thu, Nov 30, 2017 at 4:09 PM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Thu, Nov 30, 2017 at 3:13 PM, Bin.Cheng <amker.ch...@gmail.com> wrote:
>> On Thu, Nov 30, 2017 at 1:01 PM, Richard Biener
>> <richard.guent...@gmail.com> wrote:
>>> On Tue, Nov 28, 2017 at 4:26 PM, Bin Cheng <bin.ch...@arm.com> wrote:
>>>> Hi,
>>>> This is updated patch with review comments resolved. Some explanation
>>>> embedded below.
>>>>
>>>>> +
>>>>> + iloop->nb_iterations = nb_iterations;
>>>>>
>>>>> use std::swap? Also I think if you can keep nb_iterations you
>>>>> can certainly keep the upper bounds. You're probably
>>>>> afraid of the ->stmt references in the nb_iter_bound entries?
>>>>>
>>>>> Anyway, either scrap everything or try to keep everything.
>>>> Yeah, not only the stmts, but also the control_iv information because the
>>>> SCEV
>>>> information may be corrupted during code transformation.
>>>> Now I discarded all the information.
>>>
>>> Note that given you interchange the loops but not the CFG or the loop
>>> structures
>>> you might want to swap loop->num and flags like ->force_vectorize. That is,
>>> essentially change the ->header/latch association (and other CFG related
>>> stuff
>>> like recorded exits).
>>>
>>> It might also be we want to / need to disable interchange for, say,
>>> ->force_vectorize
>>> inner loops or ->unroll != 0? Or we need to clear them, maybe
>>> optionally diagnosing
>>> that fact.
>>>
>>> At least we need to think about what it means to preserve loop
>>> structure (semantically,
>>> loop->num should maintain association to the same source-level loop
>>> throughout the
>>> compilation) for transforms like interchange.
>>>
>>>>>
>>>>> + for (i = 0; oloop.reductions.iterate (i, &re); ++i)
>>>>> + {
>>>>> + if (re->type != DOUBLE_RTYPE)
>>>>> + gcc_unreachable ();
>>>>> +
>>>>> + use_operand_p use_p;
>>>>> + imm_use_iterator iterator;
>>>>> + FOR_EACH_IMM_USE_FAST (use_p, iterator, re->var)
>>>>> + mark_or_remove_dbg_stmt (USE_STMT (use_p), re->var);
>>>>> + FOR_EACH_IMM_USE_FAST (use_p, iterator, re->next)
>>>>> + mark_or_remove_dbg_stmt (USE_STMT (use_p), re->next);
>>>>> + if (TREE_CODE (re->init) == SSA_NAME)
>>>>> + {
>>>>> + FOR_EACH_IMM_USE_FAST (use_p, iterator, re->init)
>>>>> + mark_or_remove_dbg_stmt (USE_STMT (use_p), re->init);
>>>>> + }
>>>>>
>>>>> can you add a comment what you are doing here?
>>>>>
>>>>> Note that other loop opts simply scrap all debug stmts ...
>>>> As mentioned above, updated patch doesn't try hard to maintain debug use
>>>> info any more.
>>>>
>>>>>
>>>>> +static void
>>>>> +compute_access_stride (struct loop *loop_nest, struct loop *loop,
>>>>> + data_reference_p dr)
>>>>> +{
>>>>> ...
>>>>> + tree ref = DR_REF (dr);
>>>>> + tree scev_base = build_fold_addr_expr (ref);
>>>>> + tree access_size = TYPE_SIZE_UNIT (TREE_TYPE (ref));
>>>>> + tree niters = build_int_cst (sizetype, AVG_LOOP_NITER);
>>>>> + access_size = fold_build2 (MULT_EXPR, sizetype, niters, access_size);
>>>>> +
>>>>> + do {
>>>>> + tree scev_fn = analyze_scalar_evolution (loop, scev_base);
>>>>> + if (chrec_contains_undetermined (scev_fn)
>>>>> + || chrec_contains_symbols_defined_in_loop (scev_fn, loop->num))
>>>>> + break;
>>>>> ...
>>>>> + strides->safe_push (scev_step);
>>>>> + } while (loop != loop_nest && (loop = loop_outer (loop)) != NULL);
>>>>> +
>>>>>
>>>>> I _think_ you want to do
>>>>>
>>>>> scev_fn = analyze_scalar_evolution (loop, scev_base); // assuming
>>>>> DR_STMT (dr) is in loop
>>>>> scev_fn = instantiate_parameters (nest, scev_fn);
>>>>> if (chrec_contains_undetermined (scev_fn))
>>>>> return; // false?
>>>>>
>>>>> and analyze the result which should be of the form
>>>>>
>>>>> { { { init, +, step1 }_1, +, step2 }_2, + , step3 }_3 ...
>>>>>
>>>>> if canonical. I think estimate_val_by_simplify_replace isn't needed
>>>>> if you do that
>>>>> (it also looks odd to replace all vairables in step by niter...).
>>>> I replied on this in previous message, instantiate_parameters doesn't
>>>> always
>>>> give canonical form result as expected. The loop here could be seen as a
>>>> local instantiate process, right?
>>>
>>> Kind of. I'll see if I can reproduce the difference with any of your
>>> intercahnge
>>> testcases - any hint which one to look at?
>> For added tests, I think there will be no difference between the two.
>> I noticed the difference for
>> pointer cases like:
>> for (i...)
>> for (j...)
>> for (k...)
>> p[i*n*n + j*n+ k] =...
>>
>>>
>>>> Also estimate_val_by_simplify_replace is needed for pointers, where strides
>>>> are computed from niters of loops which could be non compilation time
>>>> constant.
>>>> But yes, it's an odd fixup after I failed to do anything better.
>>>
>>> But you are for example computing _1 - _2 to zero, right? Because both _1
>>> and _2 are not constant and thus you replace it with the same (symbolical)
>>> constant 'niter'.
>>>
>>> I think that asks for garbage-in-garbage-out ...
>>>
>>> Which testcase is this important for so I can have a look?
>> So far this is only for the above pointer case. Actually I don't
>> think it's that important, and thought about skip it.
>> So we don't have to do estimate_val_by_simplify_replace.
>
> Ok, I'd like to "dumb" the pass down to the level we can solve the
> bwave case (which I realize is already one of the more complicated ones).
>
> Just because it's already late for GCC 8.
For reference I'll commit the following tomorrow, will play with adding
a testcase for bwaves and doing the multiple_of_p thing we talked about.
Richard.
> Richard.
>
>> Thanks,
>> bin
>>>
>>>>>
>>>>> I think keeping the chrec in the above form is also more suitable for what
>>>>> the caller does so the outermost loop is simply
>>>>>
>>>>> loop = loop_nest;
>>>>> loop-over-all-dr-chrecs
>>>>> if (flow_loop_nested_p (loop, CHREC_LOOP (chrec)))
>>>>> loop = CHREC_LOOP (chrec);
>>>>>
>>>>> given the outermost loop is the outer evolution. If you sort the
>>>>> stride vecs from inner
>>>>> to outer you don't need prune_access_strides_not_in_loop.
>>>> Hmm, So stripping outer loops prefer inner to outer sort of strides, but
>>>> cost computation
>>>> during interchange prefers outer to inner sort because loop_nest in
>>>> tree-data-ref is sorted
>>>> in this way. Seems a single prune_* function is better than fiddling with
>>>> cost computation.
>>>
>>> Not sure how to interpret your answer... I'll see to have a more
>>> detailed suggestion
>>> after playing with the code a bit.
>>>
>>>>>
>>>>> +/* Count and return the number of loops in LOOP_NEST. */
>>>>> +
>>>>> +unsigned int
>>>>> +num_loops_in_loop_nest (struct loop *loop_nest)
>>>>> +{
>>>>> + unsigned num_loops;
>>>>> + for (num_loops = 0; loop_nest; num_loops++, loop_nest =
>>>>> loop_nest->inner)
>>>>> + ;
>>>>> + return num_loops;
>>>>>
>>>>> loop_depth (innermost) - loop_depth (nest)?
>>>> Done.
>>>>
>>>>>
>>>>> +static bool
>>>>> +should_interchange_loops (unsigned i_idx, unsigned o_idx,
>>>>> + vec<data_reference_p> datarefs,
>>>>> + bool innermost_loops_p, bool dump_info_p = true)
>>>>> +{
>>>>>
>>>>> isn't all we need associating the above CHREC to sort after the
>>>>> CHREC_RIGHTs
>>>>> and figure a permutation sequence to arrive there? That is for the local
>>>>> decision you compute here it is CHREC_RIGHT [i_idx] > CHREC_RIGHT [o_idx]
>>>>> when we should interchange?
>>>>>
>>>>> That subloop_stride_p and tracking invariant DRs looks a bit odd. For
>>>>> loops
>>>>> where a DR is invariant you simply do not have an evolution in that loop.
>>>>> You seem to simply add strides in the inner and outer loops for each DR,
>>>>> can you explain how that works? Also I guess strides bigger than the
>>>>> various cache-line size parameters should be treated 'equal'? That is,
>>>>> if we don't get any DR to a step that results in L1 cache hits because
>>>>> two DRs share a cache line the interchange is pointless?
>>>> So given below loop:
>>>>
>>>> for (int i = 0; i < M; i++)
>>>> for (int j = 0; j < M; j++)
>>>> for (int k = 0; k < M; k++)
>>>> a[k][0][i] = b[k][0][i]
>>>>
>>>> We check if memory reference is invariant wrto a loop only if it has zero
>>>> strides within
>>>> current loop nest. In this example, there is no invariant given address
>>>> changes in the
>>>> innermost loop.
>>>
>>> But they simply wouldn't take part in the sorting? That is, invariant
>>> refs in a loop
>>> shouldn't prevent it becoming more inner or more outer, no?
>>>
>>>> For strides bigger than cache-line size, it's also possible the
>>>> interchange is wanted, as
>>>> in below example:
>>>>
>>>> for (int i = 0; i < M; i++) //loop 1
>>>> for (int j = 0; j < M; j++) //loop 2
>>>> for (int k = 0; k < M; k++) //loop 3
>>>> a[j][i][k] = b[j][i][k]
>>>>
>>>> Strides for loop 1/2 are very like to be big, but after interchange, we
>>>> will have stream
>>>> access of both arrays.
>>>>
>>>> More advanced heuristics may be possible, but so far the estimation is
>>>> quite good by
>>>> checking all interchanges I looked into.
>>>>
>>>>>
>>>>> +/* Prune DATAREFS by removing any data reference not inside of LOOP. */
>>>>> +
>>>>> +static inline void
>>>>> +prune_datarefs_not_in_loop (struct loop *loop, vec<data_reference_p>
>>>>> datarefs)
>>>>> +{
>>>>> + struct data_reference *dr;
>>>>> +
>>>>> + for (unsigned i = 0; datarefs.iterate (i, &dr);)
>>>>> + if (flow_bb_inside_loop_p (loop, gimple_bb (DR_STMT (dr))))
>>>>> + i++;
>>>>> + else
>>>>> + {
>>>>> + datarefs.ordered_remove (i);
>>>>>
>>>>> that's expensive. It's better to keep moving DRs we want to keep
>>>>> when walking the array. That is, add a j you increment only when
>>>>> we keep a DR, moving *i to *j.
>>>> Done.
>>>>
>>>>>
>>>>> + if (dr->aux)
>>>>> + {
>>>>> + DR_ACCESS_STRIDE (dr)->release ();
>>>>> + free (dr->aux);
>>>>> + }
>>>>> + free_data_ref (dr);
>>>>> + }
>>>>> +}
>>>>>
>>>>> +
>>>>> + start_loop = prune_non_rectangle_loop_nest (innermost_loop,
>>>>> start_loop);
>>>>> +
>>>>>
>>>>> Hmm. If you instantiate the SCEV for the niters for each loop in the nest
>>>>> wrt the nest you can figure if it has any evolution in sth else than the
>>>>> loop (evolution_function_is_univariate_p). That is, this is not a
>>>>> problem
>>>>> until you arrive at analyzing DR strides, right? At which point you
>>>>> can check for the appropriate form?
>>>> Hmm, not really. The niter relation may not appear in SCEV of reference
>>>> addr.
>>>> For example, below loop:
>>>>
>>>> for (int i = 0; i < M; i++) //loop 1
>>>> for (int j = 0; j < M; j++) //loop 2
>>>> for (int k = 0; k < i; k++) //loop 3
>>>> a[k][0][i] = b[k][0][i]
>>>>
>>>> There is no information in data reference about i/j loops.
>>>> Anyway, I refactored the code and put this check in
>>>> proper_loop_form_for_interchange.
>>>> Simpler I think.
>>>>
>>>>>
>>>>> + if (find_data_references_in_loop (start_loop, datarefs) ==
>>>>> chrec_dont_know
>>>>> + /* Check if there is no data reference. */
>>>>> + || datarefs->length () == 0
>>>>> + /* Check if there are too many of data references. */
>>>>> + || ((int) datarefs->length ()
>>>>> + > PARAM_VALUE (PARAM_LOOP_MAX_DATAREFS_FOR_DATADEPS))
>>>>> + /* Check if there is any data reference in loop latch. We can't
>>>>> handle
>>>>> + loops which loop header and data references have different
>>>>> execution
>>>>> + times. */
>>>>> + || dataref_niters_diff_to_loop_header (*datarefs)
>>>>>
>>>>> this suggests to do your own find_data_references_in_loop so you can early
>>>>> out.
>>>> I refactored the code a bit. Now this check is in
>>>> proper_loop_form_for_interchange,
>>>> but I do customized my own data references finder. It's needed to strip
>>>> outer loops
>>>> once a difficult reference is found.
>>>>
>>>>>
>>>>> Overall the flow through the pass is a bit hard to follow given there are
>>>>> IMHO too many functions.
>>>> Yeah, I removed quite number of small functions and refactor the code a
>>>> lot. Hope this
>>>> version is more straightforward.
>>>>>
>>>>> +unsigned int
>>>>> +pass_linterchange::execute (function *fun)
>>>>> +{
>>>>> + if (number_of_loops (fun) <= 2)
>>>>> + return 0;
>>>>> +
>>>>> + bool changed_p = false;;
>>>>> + struct loop *loop;
>>>>> + vec<loop_p> loop_nest;
>>>>> + vec<data_reference_p> datarefs;
>>>>> + vec<ddr_p> ddrs;
>>>>> +
>>>>> + FOR_EACH_LOOP (loop, LI_ONLY_INNERMOST)
>>>>> + if (prepare_perfect_loop_nest (loop, &loop_nest, &datarefs, &ddrs))
>>>>> + {
>>>>> + tree_loop_interchange loop_interchange (loop_nest, datarefs,
>>>>> ddrs);
>>>>> + changed_p |= loop_interchange.interchange ();
>>>>> + }
>>>>>
>>>>> you leak datarefs/ddrs?
>>>> It was release in destructor, but I refactored it anyway. I will push the
>>>> code to branch
>>>> gcc.gnu.org/svn/gcc/branches/gimple-linterchange.
>>>>
>>>> Thanks again for the comment of you two.
>>>
>>> Digging into the code now...
>>>
>>> Richard.
>>>
>>>> Thanks,
>>>> bin
>>>> 2017-11-27 Bin Cheng <bin.ch...@arm.com>
>>>>
>>>> * Makefile.in (gimple-loop-interchange.o): New object file.
>>>> * common.opt (floop-interchange): Reuse the option from graphite.
>>>> * doc/invoke.texi (-floop-interchange): Ditto. New document.
>>>> * gimple-loop-interchange.cc: New file.
>>>> * params.def (PARAM_LOOP_INTERCHANGE_MAX_NUM_STMTS): New parameter.
>>>> (PARAM_LOOP_INTERCHANGE_STRIDE_RATIO): New parameter.
>>>> * passes.def (pass_linterchange): New pass.
>>>> * timevar.def (TV_LINTERCHANGE): New time var.
>>>> * tree-pass.h (make_pass_linterchange): New declaration.
>>>> * tree-ssa-loop-ivcanon.c (create_canonical_iv): Change to external
>>>> interchange. Record IV before/after increment in new parameters.
>>>> * tree-ssa-loop-ivopts.h (create_canonical_iv): New declaration.
>>>>
>>>> gcc/testsuite
>>>> 2017-11-27 Bin Cheng <bin.ch...@arm.com>
>>>>
>>>> * gcc.dg/tree-ssa/loop-interchange-1.c: New test.
>>>> * gcc.dg/tree-ssa/loop-interchange-2.c: New test.
>>>> * gcc.dg/tree-ssa/loop-interchange-3.c: New test.
>>>> * gcc.dg/tree-ssa/loop-interchange-4.c: New test.
>>>> * gcc.dg/tree-ssa/loop-interchange-5.c: New test.
>>>> * gcc.dg/tree-ssa/loop-interchange-6.c: New test.
>>>> * gcc.dg/tree-ssa/loop-interchange-7.c: New test.
>>>> * gcc.dg/tree-ssa/loop-interchange-8.c: New test.
>>>> * gcc.dg/tree-ssa/loop-interchange-9.c: New test.
>>>> * gcc.dg/tree-ssa/loop-interchange-10.c: New test.
>>>> * gcc.dg/tree-ssa/loop-interchange-11.c: New test.
interchange
Description: Binary data
