8257594: C2 compiled checkcast of non-null object triggers endless deoptimization/recompilation cycle

Reviewed-by: roland, vlivanov

Author: TobiHartmann

src/hotspot/share/opto/graphKit.cpp

@@ -3311,7 +3311,13 @@ Node* GraphKit::gen_checkcast(Node *obj, Node* superklass,
       case Compile::SSC_always_false:
         // It needs a null check because a null will *pass* the cast check.
         // A non-null value will always produce an exception.
-        return null_assert(obj);
+        if (!objtp->maybe_null()) {
+          builtin_throw(Deoptimization::Reason_class_check, makecon(TypeKlassPtr::make(objtp->klass())));
+          return top();
+        } else if (!too_many_traps_or_recompiles(Deoptimization::Reason_null_assert)) {
+          return null_assert(obj);
+        }
+        break; // Fall through to full check
       }
     }
   }

src/hotspot/share/opto/parse2.cpp

@@ -83,6 +83,9 @@ void Parse::array_store(BasicType bt) {
   if (stopped())  return;     // guaranteed null or range check
   if (bt == T_OBJECT) {
     array_store_check();
+    if (stopped()) {
+      return;
+    }
   }
   Node* val;                  // Oop to store
   if (big_val) {

src/hotspot/share/opto/parseHelper.cpp

@@ -89,7 +89,10 @@ void Parse::do_checkcast() {
     return;
   }
 
-  Node *res = gen_checkcast(obj, makecon(TypeKlassPtr::make(klass)) );
+  Node* res = gen_checkcast(obj, makecon(TypeKlassPtr::make(klass)));
+  if (stopped()) {
+    return;
+  }
 
   // Pop from stack AFTER gen_checkcast because it can uncommon trap and
   // the debug info has to be correct.

test/hotspot/jtreg/compiler/uncommontrap/TestNullAssertAtCheckCast.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8257594
+ * @summary Test that failing checkcast does not trigger repeated recompilation until cutoff is hit.
+ * @requires vm.compiler2.enabled
+ * @modules java.base/jdk.internal.misc
+ * @library /test/lib
+ * @build sun.hotspot.WhiteBox
+ * @run driver ClassFileInstaller sun.hotspot.WhiteBox
+ * @run main/othervm -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI
+ *                   -Xbatch -XX:CompileCommand=dontinline,compiler.uncommontrap.TestNullAssertAtCheckCast::test*
+ *                   -XX:CompileCommand=inline,compiler.uncommontrap.TestNullAssertAtCheckCast::cast
+ *                   -XX:CompileCommand=inline,compiler.uncommontrap.TestNullAssertAtCheckCast::store
+ *                   compiler.uncommontrap.TestNullAssertAtCheckCast
+ */
+
+package compiler.uncommontrap;
+
+import sun.hotspot.WhiteBox;
+
+import java.lang.reflect.Method;
+
+public class TestNullAssertAtCheckCast {
+    private static final WhiteBox WB = WhiteBox.getWhiteBox();
+    private static final int COMP_LEVEL_FULL_OPTIMIZATION = 4;
+
+    static Long cast(Object val) {
+        return (Long)val;
+    }
+
+    static void test1() {
+        try {
+            // Always fails
+            cast(new Integer(42));
+        } catch (ClassCastException cce) {
+            // Ignored
+        }
+    }
+
+    static void test2(Integer val) {
+        try {
+            // Always fails
+            cast(val);
+        } catch (ClassCastException cce) {
+            // Ignored
+        }
+    }
+
+    static void store(Object[] array, Object val) {
+        array[0] = val;
+    }
+
+    static void test3() {
+        try {
+            // Always fails
+            store(new Long[1], new Integer(42));
+        } catch (ArrayStoreException cce) {
+            // Ignored
+        }
+    }
+
+    static void test4(Integer val) {
+        try {
+            // Always fails
+            store(new Long[1], val);
+        } catch (ArrayStoreException cce) {
+            // Ignored
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        for (int i = 0; i < 1_000_000; ++i) {
+            test1();
+            test2((i % 2 == 0) ? null : 42);
+            test3();
+            test4((i % 2 == 0) ? null : 42);
+        }
+        Method method = TestNullAssertAtCheckCast.class.getDeclaredMethod("test1");
+        if (!WB.isMethodCompilable(method, COMP_LEVEL_FULL_OPTIMIZATION, false)) {
+            throw new RuntimeException("TestNullAssertAtCheckCast::test1 not compilable");
+        }
+        method = TestNullAssertAtCheckCast.class.getDeclaredMethod("test2", Integer.class);
+        if (!WB.isMethodCompilable(method, COMP_LEVEL_FULL_OPTIMIZATION, false)) {
+            throw new RuntimeException("TestNullAssertAtCheckCast::test2 not compilable");
+        }
+        method = TestNullAssertAtCheckCast.class.getDeclaredMethod("test3");
+        if (!WB.isMethodCompilable(method, COMP_LEVEL_FULL_OPTIMIZATION, false)) {
+            throw new RuntimeException("TestNullAssertAtCheckCast::test3 not compilable");
+        }
+        method = TestNullAssertAtCheckCast.class.getDeclaredMethod("test4", Integer.class);
+        if (!WB.isMethodCompilable(method, COMP_LEVEL_FULL_OPTIMIZATION, false)) {
+            throw new RuntimeException("TestNullAssertAtCheckCast::test4 not compilable");
+        }
+    }
+}
+