8223138: Small clean-up in loop-tree support

Rename predicate 'is_inner()' to 'is_innermost()' to be accurate. Added 'is_root()' predicate for root parent test in loop-tree. Changed definition of 'is_loop()' to always lazy-read the tail, since it should never be NULL. Cleanup of 'tail()' definition.

Reviewed-by: vlivanov, neliasso

src/hotspot/share/opto/loopTransform.cpp

@@ -3249,25 +3249,18 @@ bool IdealLoopTree::iteration_split( PhaseIdealLoop *phase, Node_List &old_new )
   // Clean out prior deadwood
   DCE_loop_body();
 
-
   // Look for loop-exit tests with my 50/50 guesses from the Parsing stage.
   // Replace with a 1-in-10 exit guess.
-  if (_parent /*not the root loop*/ &&
-      !_irreducible &&
-      // Also ignore the occasional dead backedge
-      !tail()->is_top()) {
+  if (!is_root() && is_loop()) {
     adjust_loop_exit_prob(phase);
   }
 
-  // Gate unrolling, RCE and peeling efforts.
-  if (!_child &&                // If not an inner loop, do not split
-      !_irreducible &&
-      _allow_optimizations &&
-      !tail()->is_top()) {     // Also ignore the occasional dead backedge
+  // Unrolling, RCE and peeling efforts, iff innermost loop.
+  if (_allow_optimizations && is_innermost()) {
     if (!_has_call) {
-        if (!iteration_split_impl(phase, old_new)) {
-          return false;
-        }
+      if (!iteration_split_impl(phase, old_new)) {
+        return false;
+      }
     } else if (policy_unswitching(phase)) {
       phase->do_unswitching(this, old_new);
     }
@@ -3540,7 +3533,7 @@ bool PhaseIdealLoop::match_fill_loop(IdealLoopTree* lpt, Node*& store, Node*& st
 
 bool PhaseIdealLoop::intrinsify_fill(IdealLoopTree* lpt) {
   // Only for counted inner loops
-  if (!lpt->is_counted() || !lpt->is_inner()) {
+  if (!lpt->is_counted() || !lpt->is_innermost()) {
     return false;
   }
 

src/hotspot/share/opto/loopnode.cpp

@@ -2946,7 +2946,7 @@ void PhaseIdealLoop::build_and_optimize(LoopOptsMode mode) {
     for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
       IdealLoopTree* lpt = iter.current();
       bool is_counted = lpt->is_counted();
-      if (!is_counted || !lpt->is_inner()) continue;
+      if (!is_counted || !lpt->is_innermost()) continue;
 
       // check for vectorized loops, any reassociation of invariants was already done
       if (is_counted && lpt->_head->as_CountedLoop()->is_unroll_only()) continue;

src/hotspot/share/opto/loopnode.hpp

@@ -615,9 +615,11 @@ public:
   // Put loop body on igvn work list
   void record_for_igvn();
 
-  bool is_loop()    { return !_irreducible && _tail && !_tail->is_top(); }
-  bool is_inner()   { return is_loop() && _child == NULL; }
-  bool is_counted() { return is_loop() && _head != NULL && _head->is_CountedLoop(); }
+  bool is_root() { return _parent == NULL; }
+  // A proper/reducible loop w/o any (occasional) dead back-edge.
+  bool is_loop() { return !_irreducible && !tail()->is_top(); }
+  bool is_counted()   { return is_loop() && _head->is_CountedLoop(); }
+  bool is_innermost() { return is_loop() && _child == NULL; }
 
   void remove_main_post_loops(CountedLoopNode *cl, PhaseIdealLoop *phase);
 
@@ -1410,14 +1412,11 @@ class CountedLoopReserveKit {
 };// class CountedLoopReserveKit
 
 inline Node* IdealLoopTree::tail() {
-// Handle lazy update of _tail field
-  Node *n = _tail;
-  //while( !n->in(0) )  // Skip dead CFG nodes
-    //n = n->in(1);
-  if (n->in(0) == NULL)
-    n = _phase->get_ctrl(n);
-  _tail = n;
-  return n;
+  // Handle lazy update of _tail field.
+  if (_tail->in(0) == NULL) {
+    _tail = _phase->get_ctrl(_tail);
+  }
+  return _tail;
 }