src/share/vm/opto/library_call.cpp

rev 5102 : opto: Optimize g1 pre_barrier in library_call.

*** 2753,2766 ****
      // Execute transformation here to avoid barrier generation in such case.
      if (_gvn.type(newval) == TypePtr::NULL_PTR)
        newval = _gvn.makecon(TypePtr::NULL_PTR);
  
      // Reference stores need a store barrier.
!     pre_barrier(true /* do_load*/,
!                 control(), base, adr, alias_idx, newval, value_type->make_oopptr(),
!                 NULL /* pre_val*/,
                  T_OBJECT);
  #ifdef _LP64
      if (adr->bottom_type()->is_ptr_to_narrowoop()) {
        Node *newval_enc = _gvn.transform(new (C) EncodePNode(newval, newval->bottom_type()->make_narrowoop()));
        if (kind == LS_xchg) {
          load_store = _gvn.transform(new (C) GetAndSetNNode(control(), mem, adr,
--- 2753,2771 ----
      // Execute transformation here to avoid barrier generation in such case.
      if (_gvn.type(newval) == TypePtr::NULL_PTR)
        newval = _gvn.makecon(TypePtr::NULL_PTR);
  
      // Reference stores need a store barrier.
!     if (kind == LS_cmpxchg) {
!       // The only known value which might get overwritten is oldval.
!       pre_barrier(false /* do_load */,
!                   control(), NULL, NULL, max_juint, NULL, NULL,
!                   oldval /* pre_val */,
                    T_OBJECT);
+     }
+     // LS_xchg: see below.
+ 
  #ifdef _LP64
      if (adr->bottom_type()->is_ptr_to_narrowoop()) {
        Node *newval_enc = _gvn.transform(new (C) EncodePNode(newval, newval->bottom_type()->make_narrowoop()));
        if (kind == LS_xchg) {
          load_store = _gvn.transform(new (C) GetAndSetNNode(control(), mem, adr,
*** 2792,2811 ****
    // main role is to prevent LoadStore nodes from being optimized away
    // when their results aren't used.
    Node* proj = _gvn.transform(new (C) SCMemProjNode(load_store));
    set_memory(proj, alias_idx);
  
-   // Add the trailing membar surrounding the access
-   insert_mem_bar(Op_MemBarCPUOrder);
-   insert_mem_bar(Op_MemBarAcquire);
- 
  #ifdef _LP64
    if (type == T_OBJECT && adr->bottom_type()->is_ptr_to_narrowoop() && kind == LS_xchg) {
      load_store = _gvn.transform(new (C) DecodeNNode(load_store, load_store->get_ptr_type()));
    }
  #endif
  
    assert(type2size[load_store->bottom_type()->basic_type()] == type2size[rtype], "result type should match");
    set_result(load_store);
    return true;
  }
  
--- 2797,2826 ----
    // main role is to prevent LoadStore nodes from being optimized away
    // when their results aren't used.
    Node* proj = _gvn.transform(new (C) SCMemProjNode(load_store));
    set_memory(proj, alias_idx);
  
  #ifdef _LP64
    if (type == T_OBJECT && adr->bottom_type()->is_ptr_to_narrowoop() && kind == LS_xchg) {
      load_store = _gvn.transform(new (C) DecodeNNode(load_store, load_store->get_ptr_type()));
    }
  #endif
  
+   // G1: Don't need to load pre_val. The old value is returned by load_store.
+   // The pre_barrier can execute after the xchg as long as no safepoint
+   // gets inserted between them.
+   if (type == T_OBJECT && kind == LS_xchg) {
+     pre_barrier(false /* do_load */,
+                 control(), NULL, NULL, max_juint, NULL, NULL,
+                 load_store /* pre_val */,
+                 T_OBJECT);
+   }
+ 
+   // Add the trailing membar surrounding the access
+   insert_mem_bar(Op_MemBarCPUOrder);
+   insert_mem_bar(Op_MemBarAcquire);
+ 
    assert(type2size[load_store->bottom_type()->basic_type()] == type2size[rtype], "result type should match");
    set_result(load_store);
    return true;
  }