[PATCH] unswitch most profitable condition first

[Richard Biener <rguenther@suse.de>]

When doing the loop unswitching re-org we promised to followup
with improvements on the cost modeling.  The following makes sure we
try to unswitch on the most profitable condition first.  As most profitable
we pick the condition leading to the edge with the highest profile count.

Note the profile is only applied when picking the first unswitching
opportunity since the profile counts are not updated with earlier
unswitchings in mind.  Further opportunities are picked in DFS order.

Bootstrapped and tested on x86_64-unknown-linux-gnu.

Any comments?

Thanks,
Richard.

	* tree-ssa-loop-unswitch.cc (unswitch_predicate::count): New.
	(unswitch_predicate::unswitch_predicate): Initialize count.
	(init_loop_unswitch_info): First collect candidates and
	determine the outermost loop to unswitch.
	(tree_ssa_unswitch_loops): First perform all guard hoisting,
	then perform unswitching on innermost loop predicates.
	(find_unswitching_predicates_for_bb): Keep track of the
	most profitable predicate to unswitch on.
	(tree_unswitch_single_loop): Unswitch given predicate if
	not NULL.
---
 gcc/tree-ssa-loop-unswitch.cc | 66 ++++++++++++++++++++++++++++-------
 1 file changed, 54 insertions(+), 12 deletions(-)

diff --git a/gcc/tree-ssa-loop-unswitch.cc b/gcc/tree-ssa-loop-unswitch.cc
index 7d6781d1505..dfe75f52f12 100644
--- a/gcc/tree-ssa-loop-unswitch.cc
+++ b/gcc/tree-ssa-loop-unswitch.cc
@@ -118,6 +118,7 @@ struct unswitch_predicate
     if (!false_range.varying_p ()
 	&& !false_range.undefined_p ())
       false_range.invert ();
+    count = e->count ();
     num = predicates->length ();
     predicates->safe_push (this);
   }
@@ -126,7 +127,8 @@ struct unswitch_predicate
   unswitch_predicate (gcond *stmt)
     : switch_p (false)
   {
-    if (EDGE_SUCC (gimple_bb (stmt), 0)->flags & EDGE_TRUE_VALUE)
+    basic_block bb = gimple_bb (stmt);
+    if (EDGE_SUCC (bb, 0)->flags & EDGE_TRUE_VALUE)
       edge_index = 0;
     else
       edge_index = 1;
@@ -134,6 +136,7 @@ struct unswitch_predicate
     tree rhs = gimple_cond_rhs (stmt);
     enum tree_code code = gimple_cond_code (stmt);
     condition = build2 (code, boolean_type_node, lhs, rhs);
+    count = EDGE_SUCC (bb, 0)->count ().max (EDGE_SUCC (bb, 1)->count ());
     if (irange::supports_p (TREE_TYPE (lhs)))
       {
 	auto range_op = range_op_handler (code, TREE_TYPE (lhs));
@@ -180,6 +183,9 @@ struct unswitch_predicate
   /* Index of the edge the predicate belongs to in the successor vector.  */
   int edge_index;
 
+  /* The profile count of this predicate.  */
+  profile_count count;
+
   /* Whether the predicate was created from a switch statement.  */
   bool switch_p;
 
@@ -206,10 +212,14 @@ static class loop *tree_unswitch_loop (class loop *, edge, tree);
 static bool tree_unswitch_single_loop (class loop *, dump_user_location_t,
 				       predicate_vector &predicate_path,
 				       unsigned loop_size, unsigned &budget,
-				       int ignored_edge_flag, bitmap);
+				       int ignored_edge_flag, bitmap,
+				       unswitch_predicate * = NULL,
+				       basic_block = NULL);
 static void
 find_unswitching_predicates_for_bb (basic_block bb, class loop *loop,
-				    vec<unswitch_predicate *> &candidates);
+				    vec<unswitch_predicate *> &candidates,
+				    unswitch_predicate *&hottest,
+				    basic_block &hottest_bb);
 static bool tree_unswitch_outer_loop (class loop *);
 static edge find_loop_guard (class loop *, vec<gimple *>&);
 static bool empty_bb_without_guard_p (class loop *, basic_block,
@@ -242,7 +252,8 @@ set_predicates_for_bb (basic_block bb, vec<unswitch_predicate *> predicates)
    Return total number of instructions in the loop.  */
 
 static unsigned
-init_loop_unswitch_info (class loop *loop)
+init_loop_unswitch_info (class loop *loop, unswitch_predicate *&hottest,
+			 basic_block &hottest_bb)
 {
   unsigned total_insns = 0;
 
@@ -259,13 +270,16 @@ init_loop_unswitch_info (class loop *loop)
       total_insns += insns;
     }
 
+  hottest = NULL;
+  hottest_bb = NULL;
   /* Find all unswitching candidates.  */
   for (unsigned i = 0; i != loop->num_nodes; i++)
     {
       /* Find a bb to unswitch on.  */
       vec<unswitch_predicate *> candidates;
       candidates.create (1);
-      find_unswitching_predicates_for_bb (bbs[i], loop, candidates);
+      find_unswitching_predicates_for_bb (bbs[i], loop, candidates,
+					  hottest, hottest_bb);
       if (!candidates.is_empty ())
 	set_predicates_for_bb (bbs[i], candidates);
       else
@@ -329,7 +343,10 @@ tree_ssa_unswitch_loops (function *fun)
 	  unswitch_predicate::predicates = new vec<unswitch_predicate *> ();
 
 	  /* Unswitch innermost loop.  */
-	  unsigned int loop_size = init_loop_unswitch_info (loop);
+	  unswitch_predicate *hottest;
+	  basic_block hottest_bb;
+	  unsigned int loop_size = init_loop_unswitch_info (loop, hottest,
+							    hottest_bb);
 	  unsigned int budget = loop_size + param_max_unswitch_insns;
 
 	  predicate_vector predicate_path;
@@ -338,7 +355,8 @@ tree_ssa_unswitch_loops (function *fun)
 	  changed_unswitch
 	    |= tree_unswitch_single_loop (loop, loc, predicate_path,
 					  loop_size, budget,
-					  ignored_edge_flag, handled);
+					  ignored_edge_flag, handled,
+					  hottest, hottest_bb);
 	  predicate_path.release ();
 
 	  for (auto predlist : bb_predicates)
@@ -449,7 +467,9 @@ is_maybe_undefined (const tree name, gimple *stmt, class loop *loop)
 
 static void
 find_unswitching_predicates_for_bb (basic_block bb, class loop *loop,
-				    vec<unswitch_predicate *> &candidates)
+				    vec<unswitch_predicate *> &candidates,
+				    unswitch_predicate *&hottest,
+				    basic_block &hottest_bb)
 {
   gimple *last, *def;
   tree use;
@@ -489,6 +509,14 @@ find_unswitching_predicates_for_bb (basic_block bb, class loop *loop,
 
       unswitch_predicate *predicate = new unswitch_predicate (stmt);
       candidates.safe_push (predicate);
+      /* If we unswitch on this predicate we isolate both paths, so
+	 pick the highest count for updating of the hottest predicate
+	 to unswitch on first.  */
+      if (!hottest || predicate->count > hottest->count)
+	{
+	  hottest = predicate;
+	  hottest_bb = bb;
+	}
     }
   else if (gswitch *stmt = safe_dyn_cast <gswitch *> (last))
     {
@@ -561,6 +589,11 @@ find_unswitching_predicates_for_bb (basic_block bb, class loop *loop,
 					  edge_index, e,
 					  edge_range[edge_index]);
 	      candidates.safe_push (predicate);
+	      if (!hottest || predicate->count > hottest->count)
+		{
+		  hottest = predicate;
+		  hottest_bb = bb;
+		}
 	    }
 	}
     }
@@ -888,13 +921,15 @@ evaluate_loop_insns_for_predicate (class loop *loop,
 
 /* Unswitch single LOOP.  PREDICATE_PATH contains so far used predicates
    for unswitching.  BUDGET is number of instruction for which we can increase
-   the loop and is updated when unswitching occurs.  */
+   the loop and is updated when unswitching occurs.  If HOTTEST is not
+   NULL then pick this candidate as the one to unswitch on.  */
 
 static bool
 tree_unswitch_single_loop (class loop *loop, dump_user_location_t loc,
 			   predicate_vector &predicate_path,
 			   unsigned loop_size, unsigned &budget,
-			   int ignored_edge_flag, bitmap handled)
+			   int ignored_edge_flag, bitmap handled,
+			   unswitch_predicate *hottest, basic_block hottest_bb)
 {
   class loop *nloop;
   bool changed = false;
@@ -939,8 +974,15 @@ tree_unswitch_single_loop (class loop *loop, dump_user_location_t loc,
 	}
       return false;
     };
-  /* Check predicates of reachable blocks.  */
-  evaluate_bbs (loop, NULL, ignored_edge_flag, check_predicates);
+
+  if (hottest)
+    {
+      predicate = hottest;
+      predicate_bb = hottest_bb;
+    }
+  else
+    /* Check predicates of reachable blocks.  */
+    evaluate_bbs (loop, NULL, ignored_edge_flag, check_predicates);
 
   if (predicate != NULL)
     {
-- 
2.35.3