Hi,
On Wed, Sep 30 2020, Jan Hubicka wrote:
>> This patch enhances the ability of IPA to reason under what conditions
>> loops in a function have known iteration counts or strides because it
>> replaces single predicates which currently hold conjunction of
>> predicates for all loops with vectors capable of holding multiple
>> predicates, each with a cumulative frequency of loops with the
>> property.
>>
>> This second property is then used by IPA-CP to much more aggressively
>> boost its heuristic score for cloning opportunities which make
>> iteration counts or strides of frequent loops compile time constant.
>>
>> gcc/ChangeLog:
>>
>> 2020-09-03 Martin Jambor <mjam...@suse.cz>
>>
>> * ipa-fnsummary.h (ipa_freqcounting_predicate): New type.
>> (ipa_fn_summary): Change the type of loop_iterations and loop_strides
>> to vectors of ipa_freqcounting_predicate.
>> (ipa_fn_summary::ipa_fn_summary): Construct the new vectors.
>> (ipa_call_estimates): New fields loops_with_known_iterations and
>> loops_with_known_strides.
>> * ipa-cp.c (hint_time_bonus): Multiply param_ipa_cp_loop_hint_bonus
>> with the expected frequencies of loops with known iteration count or
>> stride.
>> * ipa-fnsummary.c (add_freqcounting_predicate): New function.
>> (ipa_fn_summary::~ipa_fn_summary): Release the new vectors instead of
>> just two predicates.
>> (remap_hint_predicate_after_duplication): Replace with function
>> remap_freqcounting_preds_after_dup.
>> (ipa_fn_summary_t::duplicate): Use it or duplicate new vectors.
>> (ipa_dump_fn_summary): Dump the new vectors.
>> (analyze_function_body): Compute the loop property vectors.
>> (ipa_call_context::estimate_size_and_time): Calculate also
>> loops_with_known_iterations and loops_with_known_strides. Adjusted
>> dumping accordinly.
>> (remap_hint_predicate): Replace with function
>> remap_freqcounting_predicate.
>> (ipa_merge_fn_summary_after_inlining): Use it.
>> (inline_read_section): Stream loopcounting vectors instead of two
>> simple predicates.
>> (ipa_fn_summary_write): Likewise.
>> * params.opt (ipa-max-loop-predicates): New parameter.
>> * doc/invoke.texi (ipa-max-loop-predicates): Document new param.
>>
>> diff --git a/gcc/ipa-fnsummary.c b/gcc/ipa-fnsummary.c
>> index 6082f34d63f..bbbb94aa930 100644
>> --- a/gcc/ipa-fnsummary.c
>> +++ b/gcc/ipa-fnsummary.c
>> @@ -310,6 +310,36 @@ set_hint_predicate (predicate **p, predicate
>> new_predicate)
>> }
>> }
>>
>> +/* Find if NEW_PREDICATE is already in V and if so, increment its freq.
>> + Otherwise add a new item to the vector with this predicate and frerq
>> equal
>> + to add_freq, unless the number of predicates would exceed
>> MAX_NUM_PREDICATES
>> + in which case the function does nothing. */
>> +
>> +static void
>> +add_freqcounting_predicate (vec<ipa_freqcounting_predicate, va_gc> **v,
>> + const predicate &new_predicate, sreal add_freq,
>> + unsigned max_num_predicates)
>> +{
>> + if (new_predicate == false || new_predicate == true)
>> + return;
>> + ipa_freqcounting_predicate *f;
>> + for (int i = 0; vec_safe_iterate (*v, i, &f); i++)
>> + if (new_predicate == f->predicate)
>> + {
>> + f->freq += add_freq;
>> + return;
>> + }
>> + if (vec_safe_length (*v) >= max_num_predicates)
>> + /* Too many different predicates to account for. */
>> + return;
>> +
>> + ipa_freqcounting_predicate fcp;
>> + fcp.predicate = NULL;
>> + set_hint_predicate (&fcp.predicate, new_predicate);
>> + fcp.freq = add_freq;
>> + vec_safe_push (*v, fcp);
>> + return;
>> +}
>>
>> /* Compute what conditions may or may not hold given information about
>> parameters. RET_CLAUSE returns truths that may hold in a specialized
>> copy,
>> @@ -710,13 +740,17 @@ ipa_call_summary::~ipa_call_summary ()
>>
>> ipa_fn_summary::~ipa_fn_summary ()
>> {
>> - if (loop_iterations)
>> - edge_predicate_pool.remove (loop_iterations);
>> - if (loop_stride)
>> - edge_predicate_pool.remove (loop_stride);
>> + unsigned len = vec_safe_length (loop_iterations);
>> + for (unsigned i = 0; i < len; i++)
>> + edge_predicate_pool.remove ((*loop_iterations)[i].predicate);
>> + len = vec_safe_length (loop_strides);
>> + for (unsigned i = 0; i < len; i++)
>> + edge_predicate_pool.remove ((*loop_strides)[i].predicate);
>
> For edges predicates are pointers since most of them have no interesting
> predicate and thus NULL is more compact. I guess here it would make
> snese to make predicates inline. Is there a problem with vectors not
> liking non-pods?
>> vec_free (conds);
>> vec_free (size_time_table);
>> vec_free (call_size_time_table);
>> + vec_free (loop_iterations);
>> + vec_free (loop_strides);
>
> However auto_vecs should work in the brave new C++ world.
Well, the summary lives in GC memory, so I don't think I can put
auto_vecs there.
I will add a note to look into putting a predicate directly instead as a
pointer to ipa_freqcounting_predicate as a follow-up patch.
>
> The patch looks reasonable to me. Did you check how much memory it
> consumes building bigger projects? Also I am bit worried about our
> ability to use it reasonably in the heuristics since it is quite
> complicated value...
Thanks!
Martin
