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* [PATCH] Improve profile handling in switch lowering.
@ 2022-01-26 11:11 Martin Liška
  2022-03-04 13:47 ` Martin Liška
  2022-11-28 17:38 ` Jeff Law
  0 siblings, 2 replies; 6+ messages in thread
From: Martin Liška @ 2022-01-26 11:11 UTC (permalink / raw)
  To: gcc-patches

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.  */
-- 
2.34.1


^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2022-11-28 17:38 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2022-01-26 11:11 [PATCH] Improve profile handling in switch lowering Martin Liška
2022-03-04 13:47 ` Martin Liška
2022-03-24 10:22   ` Martin Liška
2022-04-07 14:00     ` Martin Liška
2022-11-28  9:53       ` Martin Liška
2022-11-28 17:38 ` Jeff Law

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