> 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.
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...
Honza
