src/share/vm/opto/graphKit.cpp

rev 10106 : 8087341: C2 doesn't optimize redundant memory operations with G1
Summary: effect of memory barrier in post barrier is too wide
Reviewed-by: duke

@@ -3147,10 +3147,23 @@
     set_memory(_gvn.transform(new ProjNode(membar, TypeFunc::Memory)),alias_idx);
   }
   return membar;
 }
 
+void GraphKit::insert_store_load_for_barrier() {
+  Node* mem = reset_memory();
+  MemBarNode* mb = MemBarNode::make(C, Op_MemBarVolatile, Compile::AliasIdxBot);
+  mb->init_req(TypeFunc::Control, control());
+  mb->init_req(TypeFunc::Memory, mem);
+  Node* membar = _gvn.transform(mb);
+  set_control(_gvn.transform(new ProjNode(membar, TypeFunc::Control)));
+  Node* newmem = _gvn.transform(new ProjNode(membar, TypeFunc::Memory));
+  set_all_memory(mem);
+  set_memory(newmem, Compile::AliasIdxRaw);
+}
+
+
 //------------------------------shared_lock------------------------------------
 // Emit locking code.
 FastLockNode* GraphKit::shared_lock(Node* obj) {
   // bci is either a monitorenter bc or InvocationEntryBci
   // %%% SynchronizationEntryBCI is redundant; use InvocationEntryBci in interfaces

@@ -3838,11 +3851,11 @@
   int adr_type = Compile::AliasIdxRaw;
   Node*   zero = __ ConI(0); // Dirty card value
   BasicType bt = T_BYTE;
 
   if (UseConcMarkSweepGC && UseCondCardMark) {
-    insert_mem_bar(Op_MemBarVolatile);   // StoreLoad barrier
+    insert_store_load_for_barrier();
     __ sync_kit(this);
   }
 
   if (UseCondCardMark) {
     // The classic GC reference write barrier is typically implemented

@@ -4278,12 +4291,11 @@
         // load the original value of the card
         Node* card_val = __ load(__ ctrl(), card_adr, TypeInt::INT, T_BYTE, Compile::AliasIdxRaw);
 
         __ if_then(card_val, BoolTest::ne, young_card); {
           sync_kit(ideal);
-          // Use Op_MemBarVolatile to achieve the effect of a StoreLoad barrier.
-          insert_mem_bar(Op_MemBarVolatile, oop_store);
+          insert_store_load_for_barrier();
           __ sync_kit(this);
 
           Node* card_val_reload = __ load(__ ctrl(), card_adr, TypeInt::INT, T_BYTE, Compile::AliasIdxRaw);
           __ if_then(card_val_reload, BoolTest::ne, dirty_card); {
             g1_mark_card(ideal, card_adr, oop_store, alias_idx, index, index_adr, buffer, tf);