8237073: [lworld] Need special handling of jlO constructor invocation

src/java.base/share/classes/java/lang/invoke/ClassSpecializer.java

@@ -152,12 +152,14 @@ private static RuntimeException newIAE(String message, Throwable cause) {
         return new IllegalArgumentException(message, cause);
     }
 
-    private static final Function<Object, Object> CREATE_RESERVATION = new Function<>() {
-        @Override
-        public Object apply(Object key) {
-            return new Object();
-        }
-    };
+    private static class CacheHolder {
+        static final Function<Object, Object> CREATE = new Function<>() {
+            @Override
+            public Object apply(Object key) {
+                return new CacheHolder();
+            }
+        };
+    }
 
     public final S findSpecies(K key) {
         // Note:  Species instantiation may throw VirtualMachineError because of
@@ -180,12 +182,12 @@ public final S findSpecies(K key) {
         // concrete class if ever.
         // The concrete class is published via SpeciesData instance
         // returned here only after the class and species data are linked together.
-        Object speciesDataOrReservation = cache.computeIfAbsent(key, CREATE_RESERVATION);
+        Object speciesDataOrReservation = cache.computeIfAbsent(key, CacheHolder.CREATE);
         // Separating the creation of a placeholder SpeciesData instance above
         // from the loading and linking a real one below ensures we can never
         // accidentally call computeIfAbsent recursively.
         S speciesData;
-        if (speciesDataOrReservation.getClass() == Object.class) {
+        if (speciesDataOrReservation.getClass() == CacheHolder.class) {
             synchronized (speciesDataOrReservation) {
                 Object existingSpeciesData = cache.get(key);
                 if (existingSpeciesData == speciesDataOrReservation) { // won the race

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java

@@ -56,6 +56,7 @@
 import static com.sun.tools.javac.resources.CompilerProperties.Fragments.DiamondInvalidArgs;
 import com.sun.tools.javac.resources.CompilerProperties.Errors;
 import com.sun.tools.javac.resources.CompilerProperties.Fragments;
+import com.sun.tools.javac.resources.CompilerProperties.Notes;
 import com.sun.tools.javac.resources.CompilerProperties.Warnings;
 import com.sun.tools.javac.tree.*;
 import com.sun.tools.javac.tree.JCTree.*;
@@ -2830,6 +2831,9 @@ public void visitNewClass(final JCNewClass tree) {
             clazztype = TreeInfo.isEnumInit(env.tree) ?
                 attribIdentAsEnumType(env, (JCIdent)clazz) :
                 attribType(clazz, env);
+            if (clazztype.tsym == syms.objectType.tsym && cdef == null && !tree.classDeclRemoved()) {
+                log.note(tree.pos(), Notes.CantInstantiateObjectDirectly);
+            }
         } finally {
             env.info.isNewClass = false;
         }

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Lower.java

@@ -2851,7 +2851,12 @@ public void visitNewClass(JCNewClass tree) {
         } else {
             tree.clazz = access(c, tree.clazz, enclOp, false);
         }
-        result = tree;
+        if (tree.clazz.type.tsym == syms.objectType.tsym) {
+            Assert.check(tree.def == null && tree.encl == null);
+            result = makeCall(make.Ident(syms.objectsType.tsym), names.newIdentity, List.nil());
+        } else {
+            result = tree;
+        }
     }
 
     // Simplify conditionals with known constant controlling expressions.

src/jdk.compiler/share/classes/com/sun/tools/javac/resources/compiler.properties

@@ -3903,3 +3903,6 @@ compiler.warn.declared.using.preview=\
 
 compiler.warn.attempt.to.synchronize.on.instance.of.value.based.class=\
     attempt to synchronize on an instance of a value-based class
+
+compiler.note.cant.instantiate.object.directly=\
+    Object cannot be instantiated directly; a subclass of Object will be instantiated instead, by invoking java.util.Objects.newIdentity()

src/jdk.compiler/share/classes/com/sun/tools/javac/util/IntHashTable.java

@@ -40,7 +40,7 @@ public class IntHashTable {
     protected int[] ints; // the image set
     protected int mask; // used to clip int's into the domain
     protected int num_bindings; // the number of mappings (including DELETED)
-    private static final Object DELETED = new Object();
+    private static final Object DELETED = new Object() {};
 
     /**
      * Construct an Object {@literal ->} int hash table.

src/jdk.compiler/share/classes/com/sun/tools/javac/util/Names.java

@@ -94,6 +94,7 @@ public static Names instance(Context context) {
     public final Name init;
     public final Name iterator;
     public final Name length;
+    public final Name newIdentity;
     public final Name next;
     public final Name ordinal;
     public final Name provider;
@@ -281,6 +282,7 @@ public Names(Context context) {
         iterator = fromString("iterator");
         length = fromString("length");
         next = fromString("next");
+        newIdentity = fromString("newIdentity");
         ordinal = fromString("ordinal");
         provider = fromString("provider");
         serialVersionUID = fromString("serialVersionUID");

src/jdk.compiler/share/classes/com/sun/tools/sjavac/CompileJavaPackages.java

@@ -208,7 +208,7 @@ public boolean transform(final CompilationService sjavac,
 
         // Prepare compilation calls
         List<Callable<CompilationSubResult>> compilationCalls = new ArrayList<>();
-        final Object lock = new Object();
+        final Object lock = new Object() {};
         for (int i = 0; i < numCompiles; i++) {
             CompileChunk cc = compileChunks[i];
             if (cc.srcs.isEmpty()) {

test/hotspot/jtreg/compiler/escapeAnalysis/TestGetClass.java

@@ -36,10 +36,10 @@
 package compiler.escapeAnalysis;
 
 public class TestGetClass {
-    static Object obj = new Object();
+    static Object obj = new Object() {};
 
     public static boolean test() {
-        if (obj.getClass() == Object.class) {
+        if (obj.getClass().getSuperclass() == Object.class) {
             synchronized (obj) {
                 return true;
             }

test/hotspot/jtreg/compiler/jvmci/jdk.vm.ci.hotspot.test/src/jdk/vm/ci/hotspot/test/ForObjectDataProvider.java

@@ -30,7 +30,7 @@ public class ForObjectDataProvider {
     public static Object[][] forObjectDataProvider() {
         return new Object[][]{
                         {TestHelper.DUMMY_CLASS_INSTANCE.objectField,
-                                        "Object[Object@" + TestHelper.DUMMY_CLASS_INSTANCE.objectField.hashCode() + "]"},
+                                        "Object[Objects$1@" + TestHelper.DUMMY_CLASS_INSTANCE.objectField.hashCode() + "]"},
                         {TestHelper.DUMMY_CLASS_INSTANCE.stringField,
                                         "Object[String:\"" + TestHelper.DUMMY_CLASS_INSTANCE.stringField + "\"]"},
                         {TestHelper.DUMMY_CLASS_INSTANCE.booleanField,

test/hotspot/jtreg/runtime/HiddenClasses/CastToParentTest.java

@@ -73,7 +73,7 @@ public static void main(String[] args) throws Throwable {
         }
 
         // Try to cast using a different mechanism.
-        new java.lang.Object().getClass().cast(hiddenClassObj);
+        new java.lang.Object() {}.getClass().getSuperclass().cast(hiddenClassObj);
     }
 
 }

test/hotspot/jtreg/runtime/modules/CCE_module_msg.java

@@ -59,7 +59,7 @@ public static void main(String[] args) throws Throwable {
     }
 
     public static void invalidObjectToDerived() {
-        java.lang.Object instance = new java.lang.Object();
+        java.lang.Object instance = java.util.Objects.newIdentity();
         int left = 23;
         int right = 42;
         try {
@@ -69,7 +69,7 @@ public static void invalidObjectToDerived() {
             throw new RuntimeException("ClassCastException wasn't thrown, test failed.");
         } catch (ClassCastException cce) {
             System.out.println(cce.toString());
-            if (!cce.getMessage().contains("class java.lang.Object cannot be cast to class Derived (java.lang.Object is in module java.base of loader 'bootstrap'; Derived is in unnamed module of loader 'app')")) {
+            if (!cce.getMessage().contains("class java.util.Objects$1 cannot be cast to class Derived (java.util.Objects$1 is in module java.base of loader 'bootstrap'; Derived is in unnamed module of loader 'app')")) {
                 throw new RuntimeException("Wrong message: " + cce.getMessage());
             }
         }

test/hotspot/jtreg/serviceability/dcmd/gc/ClassHistogramTest.java

@@ -80,7 +80,7 @@ public void run(CommandExecutor executor, String classHistogramArgs, String expa
         output.shouldMatch("^\\s+\\d+:\\s+\\d+\\s+\\d+\\s+java.lang.String " + moduleRegex + "\\s*$");
 
         /* Require at least one java.lang.Object */
-        output.shouldMatch("^\\s+\\d+:\\s+\\d+\\s+\\d+\\s+java.lang.Object " + moduleRegex + "\\s*$");
+        output.shouldMatch("^\\s+\\d+:\\s+\\d+\\s+\\d+\\s+java.util.Objects\\$1 " + moduleRegex + "\\s*$");
 
         /* Require at exactly one TestClass[] */
         output.shouldMatch("^\\s+\\d+:\\s+1\\s+\\d+\\s+" +

test/hotspot/jtreg/serviceability/tmtools/jstack/WaitNotifyThreadTest.java

@@ -38,8 +38,8 @@
 
 public class WaitNotifyThreadTest {
 
-    private Object monitor = new Object();
-    private final String OBJECT = "a java.lang.Object";
+    private Object monitor = java.util.Objects.newIdentity();
+    private final String OBJECT = "a java.util.Objects$1";
     private final String OBJECT_WAIT = "java.lang.Object.wait";
     private final String RUN_METHOD = "WaitNotifyThreadTest$WaitThread.run";
 

test/jdk/jdk/dynalink/BeanLinkerTest.java

@@ -183,7 +183,7 @@ public void afterTest() {
     public void getPropertyTest(final boolean publicLookup) throws Throwable {
         final MethodType mt = MethodType.methodType(Object.class, Object.class, String.class);
         final CallSite cs = createCallSite(publicLookup, GET_PROPERTY, mt);
-        Assert.assertEquals(cs.getTarget().invoke(new Object(), "class"), Object.class);
+        Assert.assertEquals(cs.getTarget().invoke(new Object(), "class"), java.util.Objects.newIdentity().getClass());
         Assert.assertEquals(cs.getTarget().invoke(new Date(), "class"), Date.class);
     }
 
@@ -198,7 +198,7 @@ public void getPropertyNegativeTest(final boolean publicLookup) throws Throwable
     public void getPropertyTest2(final boolean publicLookup) throws Throwable {
         final MethodType mt = MethodType.methodType(Object.class, Object.class);
         final CallSite cs = createCallSite(publicLookup, GET_PROPERTY, "class", mt);
-        Assert.assertEquals(cs.getTarget().invoke(new Object()), Object.class);
+        Assert.assertEquals(cs.getTarget().invoke(new Object()), java.util.Objects.newIdentity().getClass());
         Assert.assertEquals(cs.getTarget().invoke(new Date()), Date.class);
     }
 

test/jdk/jdk/dynalink/TrustedDynamicLinkerFactoryTest.java

@@ -193,7 +193,7 @@ public void prelinkTransformerTest() throws Throwable {
         final CallSite cs = linker.link(new SimpleRelinkableCallSite(new CallSiteDescriptor(
                 MethodHandles.publicLookup(), GET_PROPERTY, mt)));
         Assert.assertFalse(reachedPrelinkTransformer[0]);
-        Assert.assertEquals(cs.getTarget().invoke(new Object(), "class"), Object.class);
+        Assert.assertEquals(cs.getTarget().invoke(new Object(), "class"), java.util.Objects.newIdentity().getClass());
         Assert.assertTrue(reachedPrelinkTransformer[0]);
     }
 
@@ -212,7 +212,7 @@ public void internalObjectsFilterTest() throws Throwable {
         final CallSite cs = linker.link(new SimpleRelinkableCallSite(new CallSiteDescriptor(
                 MethodHandles.publicLookup(), GET_PROPERTY, mt)));
         Assert.assertFalse(reachedInternalObjectsFilter[0]);
-        Assert.assertEquals(cs.getTarget().invoke(new Object(), "class"), Object.class);
+        Assert.assertEquals(cs.getTarget().invoke(new Object(), "class"), java.util.Objects.newIdentity().getClass());
         Assert.assertTrue(reachedInternalObjectsFilter[0]);
     }
 

test/langtools/jdk/jshell/TypeNameTest.java

@@ -51,7 +51,7 @@ public void testTypeInference() {
         assertEval("import java.util.ArrayList;");
         assertEval("import java.util.Arrays;");
 
-        assertType("new Object().getClass().getSuperclass() ", "Class<?>");
+        assertType("new Object() {}.getClass().getSuperclass().getSuperclass() ", "Class<?>");
         assertType("new ArrayList().getClass().getSuperclass()", "Class<?>");
         assertType("new ArrayList().getClass()", "Class<? extends ArrayList>");
         assertType("ArrayList.class", "Class<ArrayList>");

test/langtools/jdk/jshell/VariablesTest.java

@@ -509,7 +509,7 @@ public void varDeclRedefNoInit() {
         assertVarDeclRedefNoInit("double", "d", "3.1415926", "0.0");
         assertVarDeclRedefNoInit("boolean", "n", "true", "false");
         assertVarDeclRedefNoInit("char", "c", "'x'", "'\\000'");
-        assertVarDeclRedefNoInit("Object", "o", "new Object()", IGNORE_VALUE, "null");
+        assertVarDeclRedefNoInit("Object", "o", "new String()", IGNORE_VALUE, "null");
         assertVarDeclRedefNoInit("String", "s", "\"hi\"", "null");
     }
 

test/langtools/tools/javac/T6873849.java

@@ -68,7 +68,7 @@ void test(String opt, String expect) throws Exception {
 
     void m(List t) {
         // force a note about unchecked usage
-        t.add(new Object());
+        t.add(new Object() {});
     }
 
     private File testSrc = new File(System.getProperty("test.src", "."));

test/langtools/tools/javac/TryWithResources/ResourceRedecl.java

@@ -16,17 +16,17 @@ public void test() {
         // or as a resource in a try-with-resources statement
         try {
         } catch (Exception exParam1) {
-            Object exParam1 = new Object();
+            Object exParam1 = new Object() {};
             try (java.io.FileInputStream exParam1 = new java.io.FileInputStream("foo.txt")) {
-                Object exParam1 = new Object();
+                Object exParam1 = new Object() {};
             } catch (IOException exParam1) {
             }
         }
 
         // compiler error if resource is redeclared within the try Block as a local var
         // or as an exception param of a catch clause in a try statement
         try (java.io.FileInputStream exParam2 = new java.io.FileInputStream("bar.txt")) {
-            Object exParam2 = new Object();
+            Object exParam2 = new Object() {};
             try (BufferedReader br = new BufferedReader(new FileReader("zee.txt"))) {
             } catch (IOException exParam2) {
             }

test/langtools/tools/javac/TryWithResources/TwrForVariable3.java

@@ -6,7 +6,7 @@
 public class TwrForVariable3 implements AutoCloseable {
     public static void main(String... args) {
         TwrForVariable3 v1 = new TwrForVariable3();
-        Object v2 = new Object();
+        Object v2 = new Object() {};
         Object v3 = new Object() {
             public void close() {
             }

test/langtools/tools/javac/TryWithResources/TwrVarRedeclaration.java

@@ -15,7 +15,7 @@ public static void main(String... args) {
         }
 
         try (r) {
-            Object r = new Object();
+            Object r = new Object() {};
         }
 
         try (r) {

test/langtools/tools/javac/annotations/repeatingAnnotations/InvalidRepAnnoOnCast.java

@@ -16,5 +16,5 @@ class InvalidRepAnnoOnCast {
     @Target(ElementType.TYPE_PARAMETER)
     @interface TC { T[] value(); }
 
-    String s = (@T(1) @T(2) String) new Object();
+    String s = (@T(1) @T(2) String) new Object() {};
 }

test/langtools/tools/javac/annotations/repeatingAnnotations/InvalidRepAnnoOnCast.out

@@ -1,2 +1,3 @@
 InvalidRepAnnoOnCast.java:19:17: compiler.err.invalid.repeatable.annotation.not.applicable.in.context: InvalidRepAnnoOnCast.TC
-1 error
+InvalidRepAnnoOnCast.java:19:37: compiler.err.prob.found.req: (compiler.misc.inconvertible.types: compiler.misc.anonymous.class: java.lang.Object, @InvalidRepAnnoOnCast.T(1),@InvalidRepAnnoOnCast.T(2) java.lang.String)
+2 errors

test/langtools/tools/javac/annotations/typeAnnotations/failures/common/arrays/DeclarationAnnotation.java

@@ -9,7 +9,7 @@
 class DeclarationAnnotation {
     Object e1 = new @DA int[5];
     Object e2 = new @DA String[42];
-    Object e3 = new @DA Object();
+    Object e3 = new @DA Object() {};
     Object e4 = new @DA Object() { };
 }
 

test/langtools/tools/javac/diags/examples/CantInstantiateObjectDirectly.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2021, 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.
+ */
+
+// key: compiler.note.cant.instantiate.object.directly
+
+class CantInstantiateObjectDirectly {
+    { new Object(); }
+}

test/langtools/tools/javac/generics/UnsoundInference.java

@@ -13,7 +13,7 @@
 public class UnsoundInference {
 
     public static void main(String[] args) {
-        Object[] objArray = {new Object()};
+        Object[] objArray = {new Object() {}};
         ArrayList<String> strList = new ArrayList<String>();
         transferBug(objArray, strList);
         String str = strList.get(0);

test/langtools/tools/javac/generics/diamond/8065986/T8065986a.java

@@ -10,7 +10,7 @@
 
 class T8065986a {
     T8065986a() {
-        super(new Object<>());
+        super(new Object<>() {});
     }
 
     T8065986a(boolean b) {

test/langtools/tools/javac/generics/diamond/8065986/T8065986b.java

@@ -10,7 +10,7 @@
 
 class T8065986b {
     T8065986b() {
-        this(new Object<>());
+        this(new Object<>() {});
     }
 
     T8065986b(boolean b) {

test/langtools/tools/javac/generics/inference/CaptureLowerBoundDeref.java

@@ -19,6 +19,6 @@ class CaptureLowerBoundDeref {
     <T> K<T> m(I<? extends T> arg) { return null; }
 
     void test(Wrapper<?> w) {
-        m(w.get()).take(new Object());
+        m(w.get()).take(new Object() {});
     }
 }

test/langtools/tools/javac/generics/inference/CaptureLowerBoundDeref.out

@@ -1,2 +1,2 @@
-CaptureLowerBoundDeref.java:22:19: compiler.err.cant.apply.symbol: kindname.method, take, compiler.misc.type.captureof: 1, ?, java.lang.Object, kindname.interface, CaptureLowerBoundDeref.K<T>, (compiler.misc.no.conforming.assignment.exists: (compiler.misc.inconvertible.types: java.lang.Object, compiler.misc.type.captureof: 1, ?))
+CaptureLowerBoundDeref.java:22:19: compiler.err.cant.apply.symbol: kindname.method, take, compiler.misc.type.captureof: 1, ?, compiler.misc.anonymous.class: java.lang.Object, kindname.interface, CaptureLowerBoundDeref.K<T>, (compiler.misc.no.conforming.assignment.exists: (compiler.misc.inconvertible.types: compiler.misc.anonymous.class: java.lang.Object, compiler.misc.type.captureof: 1, ?))
 1 error

test/langtools/tools/javac/implicitThis/NewBeforeOuterConstructed2.java

@@ -25,7 +25,7 @@ void f() {
         }
     }
     public static void main(String[] args) {
-        NewBeforeOuterConstructed2 c = new NewBeforeOuterConstructed2(new Object());
+        NewBeforeOuterConstructed2 c = new NewBeforeOuterConstructed2(new Object() {});
         Middle m = c.new Middle();
         m.f();
     }

test/langtools/tools/javac/lambda/T8031967.java

@@ -117,9 +117,9 @@ private void gen(StringBuilder code, int depth) {
         }
 
         code.append(".addGap(1)\n" +
-                    ".addComponent(new Object())\n" +
+                    ".addComponent(new Object() {})\n" +
                     ".addGap(1)\n" +
-                    ".addComponent(new Object())");
+                    ".addComponent(new Object() {})");
     }
 
     class JavaSource extends SimpleJavaFileObject {