8240315: Shenandoah: Rename ShLBN::get_barrier_strength()

Reviewed-by: shade

src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp

@@ -1144,7 +1144,7 @@ void ShenandoahBarrierC2Support::pin_and_expand(PhaseIdealLoop* phase) {
   Node_List clones;
   for (int i = state->load_reference_barriers_count() - 1; i >= 0; i--) {
     ShenandoahLoadReferenceBarrierNode* lrb = state->load_reference_barrier(i);
-    if (lrb->get_barrier_strength() == ShenandoahLoadReferenceBarrierNode::NONE) {
+    if (lrb->is_redundant()) {
       continue;
     }
 
@@ -1375,7 +1375,7 @@ void ShenandoahBarrierC2Support::pin_and_expand(PhaseIdealLoop* phase) {
 
   for (int i = 0; i < state->load_reference_barriers_count(); i++) {
     ShenandoahLoadReferenceBarrierNode* lrb = state->load_reference_barrier(i);
-    if (lrb->get_barrier_strength() == ShenandoahLoadReferenceBarrierNode::NONE) {
+    if (lrb->is_redundant()) {
       continue;
     }
     Node* ctrl = phase->get_ctrl(lrb);
@@ -1394,7 +1394,7 @@ void ShenandoahBarrierC2Support::pin_and_expand(PhaseIdealLoop* phase) {
   Unique_Node_List uses_to_ignore;
   for (int i = state->load_reference_barriers_count() - 1; i >= 0; i--) {
     ShenandoahLoadReferenceBarrierNode* lrb = state->load_reference_barrier(i);
-    if (lrb->get_barrier_strength() == ShenandoahLoadReferenceBarrierNode::NONE) {
+    if (lrb->is_redundant()) {
       phase->igvn().replace_node(lrb, lrb->in(ShenandoahLoadReferenceBarrierNode::ValueIn));
       continue;
     }
@@ -3190,16 +3190,15 @@ bool ShenandoahLoadReferenceBarrierNode::needs_barrier_impl(PhaseGVN* phase, Nod
   return true;
 }
 
-ShenandoahLoadReferenceBarrierNode::Strength ShenandoahLoadReferenceBarrierNode::get_barrier_strength() {
+bool ShenandoahLoadReferenceBarrierNode::is_redundant() {
   Unique_Node_List visited;
   Node_Stack stack(0);
   stack.push(this, 0);
 
-  // Look for strongest strength: go over nodes looking for STRONG ones.
-  // Stop once we encountered STRONG. Otherwise, walk until we ran out of nodes,
-  // and then the overall strength is NONE.
-  Strength strength = NONE;
-  while (strength != STRONG && stack.size() > 0) {
+  // Check if the barrier is actually useful: go over nodes looking for useful uses
+  // (e.g. memory accesses). Stop once we detected a required use. Otherwise, walk
+  // until we ran out of nodes, and then declare the barrier redundant.
+  while (stack.size() > 0) {
     Node* n = stack.node();
     if (visited.member(n)) {
       stack.pop();
@@ -3275,14 +3274,13 @@ ShenandoahLoadReferenceBarrierNode::Strength ShenandoahLoadReferenceBarrierNode:
       case Op_StrIndexOfChar:
       case Op_HasNegatives:
         // Known to require barriers
-        strength = STRONG;
-        break;
+        return false;
       case Op_CmpP: {
         if (n->in(1)->bottom_type()->higher_equal(TypePtr::NULL_PTR) ||
             n->in(2)->bottom_type()->higher_equal(TypePtr::NULL_PTR)) {
           // One of the sides is known null, no need for barrier.
         } else {
-          strength = STRONG;
+          return false;
         }
         break;
       }
@@ -3308,7 +3306,7 @@ ShenandoahLoadReferenceBarrierNode::Strength ShenandoahLoadReferenceBarrierNode:
           // Loading the constant does not require barriers: it should be handled
           // as part of GC roots already.
         } else {
-          strength = STRONG;
+          return false;
         }
         break;
       }
@@ -3329,10 +3327,10 @@ ShenandoahLoadReferenceBarrierNode::Strength ShenandoahLoadReferenceBarrierNode:
         break;
       default: {
 #ifdef ASSERT
-        fatal("Unknown node in get_barrier_strength: %s", NodeClassNames[n->Opcode()]);
+        fatal("Unknown node in is_redundant: %s", NodeClassNames[n->Opcode()]);
 #else
-        // Default to strong: better to have excess barriers, rather than miss some.
-        strength = STRONG;
+        // Default to have excess barriers, rather than miss some.
+        return false;
 #endif
       }
     }
@@ -3347,7 +3345,9 @@ ShenandoahLoadReferenceBarrierNode::Strength ShenandoahLoadReferenceBarrierNode:
       }
     }
   }
-  return strength;
+
+  // No need for barrier found.
+  return true;
 }
 
 CallStaticJavaNode* ShenandoahLoadReferenceBarrierNode::pin_and_expand_null_check(PhaseIterGVN& igvn) {

src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.hpp

@@ -231,10 +231,6 @@ class ShenandoahLoadReferenceBarrierNode : public Node {
     ValueIn
   };
 
-  enum Strength {
-    NONE, STRONG
-  };
-
 private:
   bool _native;
 
@@ -257,7 +253,7 @@ class ShenandoahLoadReferenceBarrierNode : public Node {
   virtual uint hash() const;
   virtual bool cmp( const Node &n ) const;
 
-  Strength get_barrier_strength();
+  bool is_redundant();
   CallStaticJavaNode* pin_and_expand_null_check(PhaseIterGVN& igvn);
 
 private: