8257498: Remove useless skeleton predicates

src/hotspot/share/opto/compile.cpp

@@ -390,6 +390,9 @@ void Compile::remove_useless_node(Node* dead) {
   if (dead->is_expensive()) {
     remove_expensive_node(dead);
   }
+  if (dead->Opcode() == Op_Opaque4) {
+    remove_skeleton_predicate_opaq(dead);
+  }
   if (dead->for_post_loop_opts_igvn()) {
     remove_from_post_loop_opts_igvn(dead);
   }
@@ -565,6 +568,7 @@ Compile::Compile( ciEnv* ci_env, ciMethod* target, int osr_bci,
                   _intrinsics        (comp_arena(), 0, 0, NULL),
                   _macro_nodes       (comp_arena(), 8, 0, NULL),
                   _predicate_opaqs   (comp_arena(), 8, 0, NULL),
+                  _skeleton_predicate_opaqs (comp_arena(), 8, 0, NULL),
                   _expensive_nodes   (comp_arena(), 8, 0, NULL),
                   _for_post_loop_igvn(comp_arena(), 8, 0, NULL),
                   _congraph(NULL),

src/hotspot/share/opto/compile.hpp

@@ -315,6 +315,7 @@ class Compile : public Phase {
   GrowableArray<CallGenerator*> _intrinsics;    // List of intrinsics.
   GrowableArray<Node*>  _macro_nodes;           // List of nodes which need to be expanded before matching.
   GrowableArray<Node*>  _predicate_opaqs;       // List of Opaque1 nodes for the loop predicates.
+  GrowableArray<Node*>  _skeleton_predicate_opaqs; // List of Opaque4 nodes for the loop skeleton predicates.
   GrowableArray<Node*>  _expensive_nodes;       // List of nodes that are expensive to compute and that we'd better not let the GVN freely common
   GrowableArray<Node*>  _for_post_loop_igvn;    // List of nodes for IGVN after loop opts are over
   ConnectionGraph*      _congraph;
@@ -657,11 +658,13 @@ class Compile : public Phase {
   void end_method(int level = 1);
 
   int           macro_count()             const { return _macro_nodes.length(); }
-  int           predicate_count()         const { return _predicate_opaqs.length();}
+  int           predicate_count()         const { return _predicate_opaqs.length(); }
+  int           skeleton_predicate_count() const { return _skeleton_predicate_opaqs.length(); }
   int           expensive_count()         const { return _expensive_nodes.length(); }
 
   Node*         macro_node(int idx)       const { return _macro_nodes.at(idx); }
-  Node*         predicate_opaque1_node(int idx) const { return _predicate_opaqs.at(idx);}
+  Node*         predicate_opaque1_node(int idx) const { return _predicate_opaqs.at(idx); }
+  Node*         skeleton_predicate_opaque4_node(int idx) const { return _skeleton_predicate_opaqs.at(idx); }
   Node*         expensive_node(int idx)   const { return _expensive_nodes.at(idx); }
 
   ConnectionGraph* congraph()                   { return _congraph;}
@@ -689,7 +692,15 @@ class Compile : public Phase {
     assert(_macro_nodes.contains(n), "should have already been in macro list");
     _predicate_opaqs.append(n);
   }
-
+  void add_skeleton_predicate_opaq(Node* n) {
+    assert(!_skeleton_predicate_opaqs.contains(n), "duplicate entry in skeleton predicate opaque4 list");
+    _skeleton_predicate_opaqs.append(n);
+  }
+  void remove_skeleton_predicate_opaq(Node* n) {
+    if (skeleton_predicate_count() > 0) {
+      _skeleton_predicate_opaqs.remove_if_existing(n);
+    }
+  }
   bool       post_loop_opts_phase() { return _post_loop_opts_phase;  }
   void   set_post_loop_opts_phase() { _post_loop_opts_phase = true;  }
   void reset_post_loop_opts_phase() { _post_loop_opts_phase = false; }

src/hotspot/share/opto/loopPredicate.cpp

@@ -231,33 +231,20 @@ ProjNode* PhaseIdealLoop::clone_predicate_to_unswitched_loop(ProjNode* predicate
 // the old predicates to the new cloned predicates.
 void PhaseIdealLoop::clone_skeleton_predicates_to_unswitched_loop(IdealLoopTree* loop, const Node_List& old_new, Deoptimization::DeoptReason reason,
                                                                   ProjNode* old_predicate_proj, ProjNode* iffast_pred, ProjNode* ifslow_pred) {
-  IfNode* iff = old_predicate_proj->in(0)->as_If();
   assert(iffast_pred->in(0)->is_If() && ifslow_pred->in(0)->is_If(), "sanity check");
-  ProjNode* uncommon_proj = iff->proj_out(1 - old_predicate_proj->as_Proj()->_con);
-  Node* rgn = uncommon_proj->unique_ctrl_out();
-  assert(rgn->is_Region() || rgn->is_Call(), "must be a region or call uct");
-  assert(iff->in(1)->in(1)->Opcode() == Op_Opaque1, "unexpected predicate shape");
-  Node* predicate = iff->in(0);
+  // Only need to clone range check predicates as those can be changed and duplicated by inserting pre/main/post loops
+  // and doing loop unrolling. Push the original predicates on a list to later process them in reverse order to keep the
+  // original predicate order.
   Unique_Node_List list;
-  while (predicate != NULL && predicate->is_Proj() && predicate->in(0)->is_If()) {
-    iff = predicate->in(0)->as_If();
-    uncommon_proj = iff->proj_out(1 - predicate->as_Proj()->_con);
-    if (uncommon_proj->unique_ctrl_out() != rgn)
-      break;
-    if (iff->in(1)->Opcode() == Op_Opaque4 && skeleton_predicate_has_opaque(iff)) {
-      // Only need to clone range check predicates as those can be changed and duplicated by inserting pre/main/post loops
-      // and doing loop unrolling. Push the original predicates on a list to later process them in reverse order to keep the
-      // original predicate order.
-      list.push(predicate);
-    }
-    predicate = predicate->in(0)->in(0);
-  }
+  get_skeleton_predicates(old_predicate_proj, list);
 
   Node_List to_process;
+  IfNode* iff = old_predicate_proj->in(0)->as_If();
+  ProjNode* uncommon_proj = iff->proj_out(1 - old_predicate_proj->as_Proj()->_con);
   // Process in reverse order such that 'create_new_if_for_predicate' can be used in 'clone_skeleton_predicate_for_unswitched_loops'
   // and the original order is maintained.
   for (int i = list.size() - 1; i >= 0; i--) {
-    predicate = list.at(i);
+    Node* predicate = list.at(i);
     assert(predicate->in(0)->is_If(), "must be If node");
     iff = predicate->in(0)->as_If();
     assert(predicate->is_Proj() && predicate->as_Proj()->is_IfProj(), "predicate must be a projection of an if node");
@@ -288,6 +275,34 @@ void PhaseIdealLoop::clone_skeleton_predicates_to_unswitched_loop(IdealLoopTree*
   }
 }
 
+// Put all skeleton predicate projections on a list, starting at 'predicate' and going up in the tree. If 'get_opaque'
+// is set, then the Opaque4 nodes of the skeleton predicates are put on the list instead of the projections.
+void PhaseIdealLoop::get_skeleton_predicates(Node* predicate, Unique_Node_List& list, bool get_opaque) {
+  IfNode* iff = predicate->in(0)->as_If();
+  ProjNode* uncommon_proj = iff->proj_out(1 - predicate->as_Proj()->_con);
+  Node* rgn = uncommon_proj->unique_ctrl_out();
+  assert(rgn->is_Region() || rgn->is_Call(), "must be a region or call uct");
+  assert(iff->in(1)->in(1)->Opcode() == Op_Opaque1, "unexpected predicate shape");
+  predicate = iff->in(0);
+  while (predicate != NULL && predicate->is_Proj() && predicate->in(0)->is_If()) {
+    iff = predicate->in(0)->as_If();
+    uncommon_proj = iff->proj_out(1 - predicate->as_Proj()->_con);
+    if (uncommon_proj->unique_ctrl_out() != rgn) {
+      break;
+    }
+    if (iff->in(1)->Opcode() == Op_Opaque4 && skeleton_predicate_has_opaque(iff)) {
+      if (get_opaque) {
+        // Collect the predicate Opaque4 node.
+        list.push(iff->in(1));
+      } else {
+        // Collect the predicate projection.
+        list.push(predicate);
+      }
+    }
+    predicate = predicate->in(0)->in(0);
+  }
+}
+
 // Clone a skeleton predicate for an unswitched loop. OpaqueLoopInit and OpaqueLoopStride nodes are cloned and uncommon
 // traps are kept for the predicate (a Halt node is used later when creating pre/main/post loops and copying this cloned
 // predicate again).
@@ -1241,6 +1256,7 @@ ProjNode* PhaseIdealLoop::insert_initial_skeleton_predicate(IfNode* iff, IdealLo
   register_new_node(opaque_init, upper_bound_proj);
   BoolNode* bol = rc_predicate(loop, upper_bound_proj, scale, offset, opaque_init, limit, stride, rng, (stride > 0) != (scale > 0), overflow);
   Node* opaque_bol = new Opaque4Node(C, bol, _igvn.intcon(1)); // This will go away once loop opts are over
+  C->add_skeleton_predicate_opaq(opaque_bol);
   register_new_node(opaque_bol, upper_bound_proj);
   ProjNode* new_proj = create_new_if_for_predicate(predicate_proj, NULL, reason, overflow ? Op_If : iff->Opcode());
   _igvn.replace_input_of(new_proj->in(0), 1, opaque_bol);
@@ -1258,6 +1274,7 @@ ProjNode* PhaseIdealLoop::insert_initial_skeleton_predicate(IfNode* iff, IdealLo
   register_new_node(max_value, new_proj);
   bol = rc_predicate(loop, new_proj, scale, offset, max_value, limit, stride, rng, (stride > 0) != (scale > 0), overflow);
   opaque_bol = new Opaque4Node(C, bol, _igvn.intcon(1));
+  C->add_skeleton_predicate_opaq(opaque_bol);
   register_new_node(opaque_bol, new_proj);
   new_proj = create_new_if_for_predicate(predicate_proj, NULL, reason, overflow ? Op_If : iff->Opcode());
   _igvn.replace_input_of(new_proj->in(0), 1, opaque_bol);

src/hotspot/share/opto/loopnode.cpp

@@ -3530,8 +3530,7 @@ void PhaseIdealLoop::log_loop_tree() {
 //---------------------collect_potentially_useful_predicates-----------------------
 // Helper function to collect potentially useful predicates to prevent them from
 // being eliminated by PhaseIdealLoop::eliminate_useless_predicates
-void PhaseIdealLoop::collect_potentially_useful_predicates(
-                         IdealLoopTree * loop, Unique_Node_List &useful_predicates) {
+void PhaseIdealLoop::collect_potentially_useful_predicates(IdealLoopTree* loop, Unique_Node_List &useful_predicates) {
   if (loop->_child) { // child
     collect_potentially_useful_predicates(loop->_child, useful_predicates);
   }
@@ -3542,22 +3541,28 @@ void PhaseIdealLoop::collect_potentially_useful_predicates(
       !loop->tail()->is_top()) {
     LoopNode* lpn = loop->_head->as_Loop();
     Node* entry = lpn->in(LoopNode::EntryControl);
-    Node* predicate_proj = find_predicate(entry); // loop_limit_check first
-    if (predicate_proj != NULL) { // right pattern that can be used by loop predication
+
+    Node* predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
+    if (predicate != NULL) { // right pattern that can be used by loop predication
       assert(entry->in(0)->in(1)->in(1)->Opcode() == Op_Opaque1, "must be");
       useful_predicates.push(entry->in(0)->in(1)->in(1)); // good one
       entry = skip_loop_predicates(entry);
     }
     if (UseProfiledLoopPredicate) {
-      predicate_proj = find_predicate(entry); // Predicate
-      if (predicate_proj != NULL) {
+      predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_profile_predicate);
+      if (predicate != NULL) { // right pattern that can be used by loop predication
         useful_predicates.push(entry->in(0)->in(1)->in(1)); // good one
+        get_skeleton_predicates(entry, useful_predicates, true);
         entry = skip_loop_predicates(entry);
       }
     }
-    predicate_proj = find_predicate(entry); // Predicate
-    if (predicate_proj != NULL) {
-      useful_predicates.push(entry->in(0)->in(1)->in(1)); // good one
+
+    if (UseLoopPredicate) {
+      predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
+      if (predicate != NULL) { // right pattern that can be used by loop predication
+        useful_predicates.push(entry->in(0)->in(1)->in(1)); // good one
+        get_skeleton_predicates(entry, useful_predicates, true);
+      }
     }
   }
 
@@ -3571,21 +3576,31 @@ void PhaseIdealLoop::collect_potentially_useful_predicates(
 // Note: it will also eliminates loop limits check predicate since it also uses
 // Opaque1 node (see Parse::add_predicate()).
 void PhaseIdealLoop::eliminate_useless_predicates() {
-  if (C->predicate_count() == 0)
+  if (C->predicate_count() == 0 && C->skeleton_predicate_count() == 0) {
     return; // no predicate left
+  }
 
   Unique_Node_List useful_predicates; // to store useful predicates
   if (C->has_loops()) {
     collect_potentially_useful_predicates(_ltree_root->_child, useful_predicates);
   }
 
   for (int i = C->predicate_count(); i > 0; i--) {
-     Node * n = C->predicate_opaque1_node(i-1);
+     Node* n = C->predicate_opaque1_node(i - 1);
      assert(n->Opcode() == Op_Opaque1, "must be");
      if (!useful_predicates.member(n)) { // not in the useful list
        _igvn.replace_node(n, n->in(1));
      }
   }
+
+  for (int i = C->skeleton_predicate_count(); i > 0; i--) {
+    const int idx = i - 1;
+    Node* n = C->skeleton_predicate_opaque4_node(idx);
+    assert(n->Opcode() == Op_Opaque4, "must be");
+    if (!useful_predicates.member(n)) { // not in the useful list
+      _igvn.replace_node(n, n->in(2));
+    }
+  }
 }
 
 //------------------------process_expensive_nodes-----------------------------

src/hotspot/share/opto/loopnode.hpp

@@ -914,7 +914,8 @@ class PhaseIdealLoop : public PhaseTransform {
                                                IdealLoopTree* outer_loop, Node* input_proj);
   Node* clone_skeleton_predicate_bool(Node* iff, Node* new_init, Node* new_stride, Node* predicate, Node* uncommon_proj, Node* control,
                                       IdealLoopTree* outer_loop);
-  bool skeleton_predicate_has_opaque(IfNode* iff);
+  static bool skeleton_predicate_has_opaque(IfNode* iff);
+  static void get_skeleton_predicates(Node* predicate, Unique_Node_List& list, bool get_opaque = false);
   void update_main_loop_skeleton_predicates(Node* ctrl, CountedLoopNode* loop_head, Node* init, int stride_con);
   void insert_loop_limit_check(ProjNode* limit_check_proj, Node* cmp_limit, Node* bol);
 #ifdef ASSERT

src/hotspot/share/opto/node.cpp

@@ -644,6 +644,9 @@ void Node::destruct(PhaseValues* phase) {
   if (is_expensive()) {
     compile->remove_expensive_node(this);
   }
+  if (Opcode() == Op_Opaque4) {
+    compile->remove_skeleton_predicate_opaq(this);
+  }
   if (for_post_loop_opts_igvn()) {
     compile->remove_from_post_loop_opts_igvn(this);
   }