8023597: Optimize G1 barriers code for unsafe load_store

Summary: Avoid loading old values in G1 pre-barriers for inlined unsafe load_store nodes.
Reviewed-by: kvn, tonyp
Contributed-by: Martin Doerr <martin.doerr@sap.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/share/vm/opto/graphKit.cpp b/src/share/vm/opto/graphKit.cpp
index 2f435db65..18772dfd0 100644
--- a/src/share/vm/opto/graphKit.cpp
+++ b/src/share/vm/opto/graphKit.cpp
@@ -1501,6 +1501,25 @@ void GraphKit::pre_barrier(bool do_load,
   }
 }
 
+bool GraphKit::can_move_pre_barrier() const {
+  BarrierSet* bs = Universe::heap()->barrier_set();
+  switch (bs->kind()) {
+    case BarrierSet::G1SATBCT:
+    case BarrierSet::G1SATBCTLogging:
+      return true; // Can move it if no safepoint
+
+    case BarrierSet::CardTableModRef:
+    case BarrierSet::CardTableExtension:
+    case BarrierSet::ModRef:
+      return true; // There is no pre-barrier
+
+    case BarrierSet::Other:
+    default      :
+      ShouldNotReachHere();
+  }
+  return false;
+}
+
 void GraphKit::post_barrier(Node* ctl,
                             Node* store,
                             Node* obj,
@@ -3551,6 +3570,8 @@ void GraphKit::g1_write_barrier_pre(bool do_load,
   } else {
     // In this case both val_type and alias_idx are unused.
     assert(pre_val != NULL, "must be loaded already");
+    // Nothing to be done if pre_val is null.
+    if (pre_val->bottom_type() == TypePtr::NULL_PTR) return;
     assert(pre_val->bottom_type()->basic_type() == T_OBJECT, "or we shouldn't be here");
   }
   assert(bt == T_OBJECT, "or we shouldn't be here");