8248467: C2: compiler/intrinsics/object/TestClone fails with -XX:+VerifyGraphEdges

Fix assert by taking MemBarNodes into account whose precedence edge can be NULL.

Reviewed-by: kvn, thartmann

Author: chhagedorn

src/hotspot/share/opto/node.cpp

@@ -2141,8 +2141,9 @@ void Node::verify_edges(Unique_Node_List &visited) {
       }
       assert( cnt == 0,"Mismatched edge count.");
     } else if (n == NULL) {
-      assert(i >= req() || i == 0 || is_Region() || is_Phi() || is_ArrayCopy()
-              || (is_Unlock() && i == req()-1), "only region, phi, arraycopy or unlock nodes have null data edges");
+      assert(i >= req() || i == 0 || is_Region() || is_Phi() || is_ArrayCopy() || (is_Unlock() && i == req()-1)
+              || (is_MemBar() && i == 5), // the precedence edge to a membar can be removed during macro node expansion
+              "only region, phi, arraycopy, unlock or membar nodes have null data edges");
     } else {
       assert(n->is_top(), "sanity");
       // Nothing to check.

test/hotspot/jtreg/compiler/intrinsics/object/TestClone.java

@@ -23,7 +23,7 @@
 
 /*
  * @test
- * @bug 8033626 8246453
+ * @bug 8033626 8246453 8248467
  * @summary assert(ex_map->jvms()->same_calls_as(_exceptions->jvms())) failed: all collected exceptions must come from the same place
  * @modules java.base/jdk.internal.misc
  * @library /test/lib
@@ -35,6 +35,10 @@
  *      -XX:+IgnoreUnrecognizedVMOptions -XX:+StressReflectiveCode
  *      -XX:CompileCommand=compileonly,compiler.intrinsics.object.TestClone::test*
  *      compiler.intrinsics.object.TestClone
+ * @run main/othervm -XX:-TieredCompilation -Xbatch
+ *      -XX:+IgnoreUnrecognizedVMOptions -XX:+StressReflectiveCode -XX:+VerifyGraphEdges
+ *      -XX:CompileCommand=compileonly,compiler.intrinsics.object.TestClone::test*
+ *      compiler.intrinsics.object.TestClone
  */
 
 package compiler.intrinsics.object;