Re: [PATCH] Improve profile handling in switch lowering.

["Martin Liška" <mliska@suse.cz>]

PING^3

On 3/24/22 11:22, Martin Liška wrote:
> PING^2
> 
> On 3/4/22 14:47, Martin Liška wrote:
>> PING^1
>>
>> On 1/26/22 12:11, Martin Liška wrote:
>>> Hello.
>>>
>>> Right now, switch lowering does not update basic_block::count values
>>> so that they are uninitiliazed. Moreover, I've updated probability scaling
>>> when a more complex expansion happens. There are still some situations where
>>> the profile is a bit imprecise, but the patch improves rapidly the current situation.
>>>
>>> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
>>>
>>> Ready to be installed?
>>> Thanks,
>>> Martin
>>>
>>>      PR tree-optimization/101301
>>>      PR tree-optimization/103680
>>>
>>> gcc/ChangeLog:
>>>
>>>      * tree-switch-conversion.cc (bit_test_cluster::emit):
>>>      Handle correctly remaining probability.
>>>      (switch_decision_tree::try_switch_expansion): Fix BB's count
>>>      where a cluster expansion happens.
>>>      (switch_decision_tree::emit_cmp_and_jump_insns): Fill up also
>>>      BB count.
>>>      (switch_decision_tree::do_jump_if_equal): Likewise.
>>>      (switch_decision_tree::emit_case_nodes): Handle special case
>>>      for BT expansion which can also fallback to a default BB.
>>>      * tree-switch-conversion.h (cluster::cluster): Add
>>>      m_default_prob probability.
>>> ---
>>>   gcc/tree-switch-conversion.cc | 51 ++++++++++++++++++++++++-----------
>>>   gcc/tree-switch-conversion.h  |  8 +++++-
>>>   2 files changed, 43 insertions(+), 16 deletions(-)
>>>
>>> diff --git a/gcc/tree-switch-conversion.cc b/gcc/tree-switch-conversion.cc
>>> index 670397c87e4..d6679e8dee3 100644
>>> --- a/gcc/tree-switch-conversion.cc
>>> +++ b/gcc/tree-switch-conversion.cc
>>> @@ -1538,10 +1538,12 @@ bit_test_cluster::emit (tree index_expr, tree index_type,
>>>         test[k].target_bb = n->m_case_bb;
>>>         test[k].label = n->m_case_label_expr;
>>>         test[k].bits = 0;
>>> +      test[k].prob = profile_probability::never ();
>>>         count++;
>>>       }
>>>
>>>         test[k].bits += n->get_range (n->get_low (), n->get_high ());
>>> +      test[k].prob += n->m_prob;
>>>
>>>         lo = tree_to_uhwi (int_const_binop (MINUS_EXPR, n->get_low (), minval));
>>>         if (n->get_high () == NULL_TREE)
>>> @@ -1629,6 +1631,11 @@ bit_test_cluster::emit (tree index_expr, tree index_type,
>>>                     /*simple=*/true, NULL_TREE,
>>>                     /*before=*/true, GSI_SAME_STMT);
>>>
>>> +  profile_probability subtree_prob = m_subtree_prob;
>>> +  profile_probability default_prob = m_default_prob;
>>> +  if (!default_prob.initialized_p ())
>>> +    default_prob = m_subtree_prob.invert ();
>>> +
>>>     if (m_handles_entire_switch && entry_test_needed)
>>>       {
>>>         tree range = int_const_binop (MINUS_EXPR, maxval, minval);
>>> @@ -1639,9 +1646,10 @@ bit_test_cluster::emit (tree index_expr, tree index_type,
>>>                       /*simple=*/true, NULL_TREE,
>>>                       /*before=*/true, GSI_SAME_STMT);
>>>         tmp = fold_build2 (GT_EXPR, boolean_type_node, idx, range);
>>> +      default_prob = default_prob.apply_scale (1, 2);
>>>         basic_block new_bb
>>>       = hoist_edge_and_branch_if_true (&gsi, tmp, default_bb,
>>> -                     profile_probability::unlikely ());
>>> +                     default_prob);
>>>         gsi = gsi_last_bb (new_bb);
>>>       }
>>>
>>> @@ -1662,14 +1670,12 @@ bit_test_cluster::emit (tree index_expr, tree index_type,
>>>     else
>>>       csui = tmp;
>>>
>>> -  profile_probability prob = profile_probability::always ();
>>> -
>>>     /* for each unique set of cases:
>>>          if (const & csui) goto target  */
>>>     for (k = 0; k < count; k++)
>>>       {
>>> -      prob = profile_probability::always ().apply_scale (test[k].bits,
>>> -                             bt_range);
>>> +      profile_probability prob = test[k].prob / (subtree_prob + default_prob);
>>> +      subtree_prob -= test[k].prob;
>>>         bt_range -= test[k].bits;
>>>         tmp = wide_int_to_tree (word_type_node, test[k].mask);
>>>         tmp = fold_build2 (BIT_AND_EXPR, word_type_node, csui, tmp);
>>> @@ -1908,9 +1914,13 @@ switch_decision_tree::try_switch_expansion (vec<cluster *> &clusters)
>>>         /* Emit cluster-specific switch handling.  */
>>>         for (unsigned i = 0; i < clusters.length (); i++)
>>>       if (clusters[i]->get_type () != SIMPLE_CASE)
>>> -      clusters[i]->emit (index_expr, index_type,
>>> -                 gimple_switch_default_label (m_switch),
>>> -                 m_default_bb, gimple_location (m_switch));
>>> +      {
>>> +        edge e = single_pred_edge (clusters[i]->m_case_bb);
>>> +        e->dest->count = e->src->count.apply_probability (e->probability);
>>> +        clusters[i]->emit (index_expr, index_type,
>>> +                   gimple_switch_default_label (m_switch),
>>> +                   m_default_bb, gimple_location (m_switch));
>>> +      }
>>>       }
>>>
>>>     fix_phi_operands_for_edges ();
>>> @@ -2162,6 +2172,7 @@ switch_decision_tree::emit_cmp_and_jump_insns (basic_block bb, tree op0,
>>>     edge false_edge = split_block (bb, cond);
>>>     false_edge->flags = EDGE_FALSE_VALUE;
>>>     false_edge->probability = prob.invert ();
>>> +  false_edge->dest->count = bb->count.apply_probability (prob.invert ());
>>>
>>>     edge true_edge = make_edge (bb, label_bb, EDGE_TRUE_VALUE);
>>>     true_edge->probability = prob;
>>> @@ -2192,6 +2203,7 @@ switch_decision_tree::do_jump_if_equal (basic_block bb, tree op0, tree op1,
>>>     edge false_edge = split_block (bb, cond);
>>>     false_edge->flags = EDGE_FALSE_VALUE;
>>>     false_edge->probability = prob.invert ();
>>> +  false_edge->dest->count = bb->count.apply_probability (prob.invert ());
>>>
>>>     edge true_edge = make_edge (bb, label_bb, EDGE_TRUE_VALUE);
>>>     true_edge->probability = prob;
>>> @@ -2227,7 +2239,7 @@ switch_decision_tree::emit_case_nodes (basic_block bb, tree index,
>>>                    node->m_c->m_case_bb, p, loc);
>>>         /* Since this case is taken at this point, reduce its weight from
>>>        subtree_weight.  */
>>> -      node->m_c->m_subtree_prob -= p;
>>> +      node->m_c->m_subtree_prob -= node->m_c->m_prob;
>>>
>>>         if (node->m_left != NULL && node->m_right != NULL)
>>>       {
>>> @@ -2246,6 +2258,7 @@ switch_decision_tree::emit_case_nodes (basic_block bb, tree index,
>>>              / (node->m_c->m_subtree_prob + default_prob));
>>>             bb = do_jump_if_equal (bb, index, node->m_right->m_c->get_low (),
>>>                        node->m_right->m_c->m_case_bb, p, loc);
>>> +          node->m_c->m_subtree_prob -= node->m_right->m_c->m_prob;
>>>
>>>             p = (node->m_left->m_c->m_prob
>>>              / (node->m_c->m_subtree_prob + default_prob));
>>> @@ -2262,6 +2275,7 @@ switch_decision_tree::emit_case_nodes (basic_block bb, tree index,
>>>             p = ((node->m_right->m_c->m_subtree_prob
>>>               + default_prob.apply_scale (1, 2))
>>>              / (node->m_c->m_subtree_prob + default_prob));
>>> +          test_bb->count = bb->count.apply_probability (p);
>>>             bb = emit_cmp_and_jump_insns (bb, index, node->m_c->get_high (),
>>>                           GT_EXPR, test_bb, p, loc);
>>>             default_prob = default_prob.apply_scale (1, 2);
>>> @@ -2348,21 +2362,28 @@ switch_decision_tree::emit_case_nodes (basic_block bb, tree index,
>>>        is the one to branch to.  */
>>>         if (node->has_child () || node->m_c->get_type () != SIMPLE_CASE)
>>>       {
>>> +      bool is_bt = node->m_c->get_type () == BIT_TEST;
>>> +      int parts = is_bt ? 3 : 2;
>>> +
>>>         /* Branch to a label where we will handle it later.  */
>>>         basic_block test_bb = split_edge (single_succ_edge (bb));
>>>         redirect_edge_succ (single_pred_edge (test_bb),
>>>                     single_succ_edge (bb)->dest);
>>>
>>> -
>>> -       profile_probability right_prob = profile_probability::never ();
>>> -       if (node->m_right)
>>> -         right_prob = node->m_right->m_c->m_subtree_prob;
>>> -      p = ((right_prob + default_prob.apply_scale (1, 2))
>>> +      profile_probability right_prob = profile_probability::never ();
>>> +      if (node->m_right)
>>> +        right_prob = node->m_right->m_c->m_subtree_prob;
>>> +      p = ((right_prob + default_prob.apply_scale (1, parts))
>>>              / (node->m_c->m_subtree_prob + default_prob));
>>> +      test_bb->count = bb->count.apply_probability (p);
>>>
>>>         bb = emit_cmp_and_jump_insns (bb, index, node->m_c->get_high (),
>>>                       GT_EXPR, test_bb, p, loc);
>>> -      default_prob = default_prob.apply_scale (1, 2);
>>> +
>>> +      default_prob = default_prob.apply_scale (1, parts);
>>> +      node->m_c->m_subtree_prob -= right_prob;
>>> +      if (is_bt)
>>> +        node->m_c->m_default_prob = default_prob;
>>>
>>>         /* Value belongs to this node or to the left-hand subtree.  */
>>>         p = node->m_c->m_prob / (node->m_c->m_subtree_prob + default_prob);
>>> diff --git a/gcc/tree-switch-conversion.h b/gcc/tree-switch-conversion.h
>>> index e969c051a05..5f3f99353ba 100644
>>> --- a/gcc/tree-switch-conversion.h
>>> +++ b/gcc/tree-switch-conversion.h
>>> @@ -102,6 +102,10 @@ public:
>>>     /* Probability of reaching subtree rooted at this node.  */
>>>     profile_probability m_subtree_prob;
>>>
>>> +  /* Probability of default case when reaching the node.
>>> +     It is used by bit-test right now.  */
>>> +  profile_probability m_default_prob;
>>> +
>>>   protected:
>>>     /* Default constructor.  */
>>>     cluster () {}
>>> @@ -110,7 +114,8 @@ protected:
>>>   cluster::cluster (tree case_label_expr, basic_block case_bb,
>>>             profile_probability prob, profile_probability subtree_prob):
>>>     m_case_label_expr (case_label_expr), m_case_bb (case_bb), m_prob (prob),
>>> -  m_subtree_prob (subtree_prob)
>>> +  m_subtree_prob (subtree_prob),
>>> +  m_default_prob (profile_probability::uninitialized ())
>>>   {
>>>   }
>>>
>>> @@ -542,6 +547,7 @@ public:
>>>     basic_block target_bb;
>>>     tree label;
>>>     int bits;
>>> +  profile_probability prob;
>>>
>>>     /* Comparison function for qsort to order bit tests by decreasing
>>>        probability of execution.  */
>>
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