7143491: G1 C2 CTW: assert(p2x->outcnt() == 2) failed: expects 2 users: Xor and URShift nodes

Adjust the assert and code in eliminate_card_mark() method for case when stored value is NULL.

Reviewed-by: iveresov, never

hotspot/src/share/vm/opto/graphKit.cpp

@@ -1522,6 +1522,11 @@ Node* GraphKit::store_oop(Node* ctl,
                           const TypeOopPtr* val_type,
                           BasicType bt,
                           bool use_precise) {
+  // Transformation of a value which could be NULL pointer (CastPP #NULL)
+  // could be delayed during Parse (for example, in adjust_map_after_if()).
+  // Execute transformation here to avoid barrier generation in such case.
+  if (_gvn.type(val) == TypePtr::NULL_PTR)
+    val = _gvn.makecon(TypePtr::NULL_PTR);
 
   set_control(ctl);
   if (stopped()) return top(); // Dead path ?

hotspot/src/share/vm/opto/library_call.cpp

@@ -2678,7 +2678,13 @@ bool LibraryCallKit::inline_unsafe_CAS(BasicType type) {
     cas = _gvn.transform(new (C, 5) CompareAndSwapLNode(control(), mem, adr, newval, oldval));
     break;
   case T_OBJECT:
-     // reference stores need a store barrier.
+    // Transformation of a value which could be NULL pointer (CastPP #NULL)
+    // could be delayed during Parse (for example, in adjust_map_after_if()).
+    // 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.
     // (They don't if CAS fails, but it isn't worth checking.)
     pre_barrier(true /* do_load*/,
                 control(), base, adr, alias_idx, newval, value_type->make_oopptr(),

hotspot/src/share/vm/opto/macro.cpp

@@ -234,11 +234,20 @@ void PhaseMacroExpand::eliminate_card_mark(Node* p2x) {
     }
   } else {
     // G1 pre/post barriers
-    assert(p2x->outcnt() == 2, "expects 2 users: Xor and URShift nodes");
+    assert(p2x->outcnt() <= 2, "expects 1 or 2 users: Xor and URShift nodes");
     // It could be only one user, URShift node, in Object.clone() instrinsic
     // but the new allocation is passed to arraycopy stub and it could not
     // be scalar replaced. So we don't check the case.
 
+    // An other case of only one user (Xor) is when the value check for NULL
+    // in G1 post barrier is folded after CCP so the code which used URShift
+    // is removed.
+
+    // Take Region node before eliminating post barrier since it also
+    // eliminates CastP2X node when it has only one user.
+    Node* this_region = p2x->in(0);
+    assert(this_region != NULL, "");
+
     // Remove G1 post barrier.
 
     // Search for CastP2X->Xor->URShift->Cmp path which
@@ -263,8 +272,6 @@ void PhaseMacroExpand::eliminate_card_mark(Node* p2x) {
     // Remove G1 pre barrier.
 
     // Search "if (marking != 0)" check and set it to "false".
-    Node* this_region = p2x->in(0);
-    assert(this_region != NULL, "");
     // There is no G1 pre barrier if previous stored value is NULL
     // (for example, after initialization).
     if (this_region->is_Region() && this_region->req() == 3) {
@@ -292,7 +299,7 @@ void PhaseMacroExpand::eliminate_card_mark(Node* p2x) {
     }
     // Now CastP2X can be removed since it is used only on dead path
     // which currently still alive until igvn optimize it.
-    assert(p2x->unique_out()->Opcode() == Op_URShiftX, "");
+    assert(p2x->outcnt() == 0 || p2x->unique_out()->Opcode() == Op_URShiftX, "");
     _igvn.replace_node(p2x, top());
   }
 }