8356453: C2: assert(!vbox->is_Phi()) during vector box expansion

Reviewed-by: thartmann, kvn

Author: Vladimir Ivanov

src/hotspot/share/opto/vector.cpp

@@ -44,6 +44,10 @@ void PhaseVector::optimize_vector_boxes() {
 
   C->igvn_worklist()->ensure_empty(); // should be done with igvn
 
+  if (StressMacroExpansion) {
+    C->shuffle_macro_nodes();
+  }
+
   expand_vunbox_nodes();
   scalarize_vbox_nodes();
 
@@ -311,7 +315,7 @@ Node* PhaseVector::expand_vbox_node_helper(Node* vbox,
                                            VectorSet &visited) {
   // JDK-8304948 shows an example that there may be a cycle in the graph.
   if (visited.test_set(vbox->_idx)) {
-    assert(vbox->is_Phi(), "should be phi");
+    assert(vbox->is_Phi() || vbox->is_CheckCastPP(), "either phi or expanded");
     return vbox; // already visited
   }
 
@@ -362,7 +366,7 @@ Node* PhaseVector::expand_vbox_node_helper(Node* vbox,
     return C->initial_gvn()->transform(vbox);
   }
 
-  assert(!vbox->is_Phi(), "should be expanded");
+  assert(vbox->is_CheckCastPP(), "should be expanded");
   // TODO: assert that expanded vbox is initialized with the same value (vect).
   return vbox; // already expanded
 }

test/hotspot/jtreg/compiler/vectorapi/VectorBoxExpandTest.java

@@ -41,6 +41,7 @@ public class VectorBoxExpandTest {
 
     private static int[] iarr = new int[ARR_LEN];
     private static IntVector g;
+    private static int acc = 0;
 
     // C2 would generate IR graph like below:
     //
@@ -86,10 +87,14 @@ private static void test() {
 
         for (int ic = 0; ic < NUM_ITER; ic++) {
             for (int i = 0; i < iarr.length; i++) {
+                acc += System.identityHashCode(a);
                 a = a.add(a);
+                acc += System.identityHashCode(a);
             }
         }
         g = a;
+        acc += System.identityHashCode(a);
+
     }
 
     public static void main(String[] args) {