8260637: Shenandoah: assert(_base == Tuple) failure during C2 compilation

Reviewed-by: chagedorn, kvn

Author: rwestrel

src/hotspot/share/opto/loopnode.cpp

@@ -5301,7 +5301,7 @@ void PhaseIdealLoop::build_loop_late_post_work(Node *n, bool pinned) {
     case Op_HasNegatives:
       pinned = false;
     }
-    if (n->is_CMove()) {
+    if (n->is_CMove() || n->is_ConstraintCast()) {
       pinned = false;
     }
     if( pinned ) {

test/hotspot/jtreg/gc/shenandoah/compiler/LRBRightAfterMemBar.java

@@ -23,7 +23,7 @@
 
 /**
  * @test
- * @bug 8237007
+ * @bug 8237007 8260637
  * @summary Shenandoah: assert(_base == Tuple) failure during C2 compilation
  * @requires vm.flavor == "server"
  * @requires vm.gc.Shenandoah
@@ -33,18 +33,19 @@
  */
 
 public class LRBRightAfterMemBar {
-    private static Object field1;
+    private static A field1;
     private static Object field2;
     static volatile int barrier;
 
     public static void main(String[] args) {
         for (int i = 0; i < 20_000; i++) {
-            test(true, true, new Object());
-            test(false, false, new Object());
+            test1(true, true, new Object());
+            test1(false, false, new Object());
+            test2(new Object(), 0, 10);
         }
     }
 
-    private static Object test(boolean flag, boolean flag2, Object o2) {
+    private static Object test1(boolean flag, boolean flag2, Object o2) {
         for (int i = 0; i < 10; i++) {
             barrier = 0x42; // Membar
             if (o2 == null) { // hoisted out of loop
@@ -61,4 +62,30 @@ private static Object test(boolean flag, boolean flag2, Object o2) {
 
         return null;
     }
+
+    private static int test2(Object o2, int start, int stop) {
+        A a1 = null;
+        A a2 = null;
+        int v = 0;
+        for (int i = start; i < stop; i++) {
+            a2 = new A();
+            a1 = new A();
+            a1.a = a2;
+            barrier = 0x42; // Membar
+            if (o2 == null) { // hoisted out of loop
+            }
+            A a3 = a1.a;
+            v = a3.f; // null check optimized out by EA but CastPP left in
+        }
+
+        a1.f = 0x42;
+        a2.f = 0x42;
+
+        return v;
+    }
+
+    static class A {
+        A a;
+        int f;
+    }
 }