src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.cpp

rev 56771 : 8233401: Shenandoah: Refactor/cleanup Shenandoah load barrier code

@@ -21,10 +21,11 @@
  *
  */
 
 #include "precompiled.hpp"
 #include "gc/shared/barrierSet.hpp"
+#include "gc/shenandoah/shenandoahConcurrentRoots.hpp"
 #include "gc/shenandoah/shenandoahForwarding.hpp"
 #include "gc/shenandoah/shenandoahHeap.hpp"
 #include "gc/shenandoah/shenandoahHeuristics.hpp"
 #include "gc/shenandoah/shenandoahRuntime.hpp"
 #include "gc/shenandoah/shenandoahThreadLocalData.hpp"

@@ -532,59 +533,62 @@
   }
   return BarrierSetC2::store_at_resolved(access, val);
 }
 
 Node* ShenandoahBarrierSetC2::load_at_resolved(C2Access& access, const Type* val_type) const {
-  DecoratorSet decorators = access.decorators();
-
-  Node* adr = access.addr().node();
-  Node* obj = access.base();
+  // 1: load reference
+  Node* load = BarrierSetC2::load_at_resolved(access, val_type);
+  // For none-reference load, no additional barrier is needed
+  if (!access.is_oop()) {
+    return load;
+  }
 
-  bool mismatched = (decorators & C2_MISMATCHED) != 0;
-  bool unknown = (decorators & ON_UNKNOWN_OOP_REF) != 0;
-  bool on_heap = (decorators & IN_HEAP) != 0;
-  bool on_weak_ref = (decorators & (ON_WEAK_OOP_REF | ON_PHANTOM_OOP_REF)) != 0;
-  bool is_unordered = (decorators & MO_UNORDERED) != 0;
-  bool need_cpu_mem_bar = !is_unordered || mismatched || !on_heap;
-  bool is_traversal_mode = ShenandoahHeap::heap()->is_traversal_mode();
-  bool keep_alive = (decorators & AS_NO_KEEPALIVE) == 0 || is_traversal_mode;
+  DecoratorSet decorators = access.decorators();
   bool in_native = (decorators & IN_NATIVE) != 0;
 
-  Node* top = Compile::current()->top();
-
-  Node* offset = adr->is_AddP() ? adr->in(AddPNode::Offset) : top;
-  Node* load = BarrierSetC2::load_at_resolved(access, val_type);
-
-  if (access.is_oop()) {
+  // 2: apply LRB if ShenandoahLoadRefBarrier is set
     if (ShenandoahLoadRefBarrier) {
-      load = new ShenandoahLoadReferenceBarrierNode(NULL, load, in_native && !is_traversal_mode);
+    // Native barrier is for concurrent root processing
+    bool use_native_barrier = in_native && ShenandoahConcurrentRoots::can_do_concurrent_roots();
+    load = new ShenandoahLoadReferenceBarrierNode(NULL, load, use_native_barrier);
       if (access.is_parse_access()) {
         load = static_cast<C2ParseAccess &>(access).kit()->gvn().transform(load);
       } else {
         load = static_cast<C2OptAccess &>(access).gvn().transform(load);
       }
     }
-  }
+
+  // 3: apply keep-alive barrier if ShenandoahKeepAliveBarrier is set
+  if (ShenandoahKeepAliveBarrier) {
+    Node* top = Compile::current()->top();
+    Node* adr = access.addr().node();
+    Node* offset = adr->is_AddP() ? adr->in(AddPNode::Offset) : top;
+    Node* obj = access.base();
+
+    bool unknown = (decorators & ON_UNKNOWN_OOP_REF) != 0;
+    bool on_weak_ref = (decorators & (ON_WEAK_OOP_REF | ON_PHANTOM_OOP_REF)) != 0;
+    bool is_traversal_mode = ShenandoahHeap::heap()->is_traversal_mode();
+    bool keep_alive = (decorators & AS_NO_KEEPALIVE) == 0 || is_traversal_mode;
 
   // If we are reading the value of the referent field of a Reference
   // object (either by using Unsafe directly or through reflection)
   // then, if SATB is enabled, we need to record the referent in an
   // SATB log buffer using the pre-barrier mechanism.
   // Also we need to add memory barrier to prevent commoning reads
   // from this field across safepoint since GC can change its value.
-  bool need_read_barrier = ShenandoahKeepAliveBarrier &&
-    (on_weak_ref || (unknown && offset != top && obj != top));
-
-  if (!access.is_oop() || !need_read_barrier) {
+    if (!on_weak_ref || (unknown && (offset == top || obj == top)) || !keep_alive) {
     return load;
   }
 
   assert(access.is_parse_access(), "entry not supported at optimization time");
   C2ParseAccess& parse_access = static_cast<C2ParseAccess&>(access);
   GraphKit* kit = parse_access.kit();
+    bool mismatched = (decorators & C2_MISMATCHED) != 0;
+    bool is_unordered = (decorators & MO_UNORDERED) != 0;
+    bool need_cpu_mem_bar = !is_unordered || mismatched || in_native;
 
-  if (on_weak_ref && keep_alive) {
+    if (on_weak_ref) {
     // Use the pre-barrier to record the value in the referent field
     satb_write_barrier_pre(kit, false /* do_load */,
                            NULL /* obj */, NULL /* adr */, max_juint /* alias_idx */, NULL /* val */, NULL /* val_type */,
                            load /* pre_val */, T_OBJECT);
     // Add memory barrier to prevent commoning reads from this field

@@ -593,10 +597,11 @@
   } else if (unknown) {
     // We do not require a mem bar inside pre_barrier if need_mem_bar
     // is set: the barriers would be emitted by us.
     insert_pre_barrier(kit, obj, offset, load, !need_cpu_mem_bar);
   }
+  }
 
   return load;
 }
 
 Node* ShenandoahBarrierSetC2::atomic_cmpxchg_val_at_resolved(C2AtomicParseAccess& access, Node* expected_val,