8348606: [lworld] Substitutability test may perform heap allocations

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2008, 2025, 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
@@ -1642,6 +1642,10 @@ public MethodHandle serializableConstructor(Class<?> decl, Constructor<?> ctorTo
                 return IMPL_LOOKUP.serializableConstructor(decl, ctorToCall);
             }
 
+            @Override
+            public MethodHandle assertAsType(MethodHandle original, MethodType assertedType) {
+                return original.viewAsType(assertedType, false);
+            }
         });
     }
 

src/java.base/share/classes/java/lang/runtime/ValueObjectMethods.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2025, 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
@@ -45,12 +45,14 @@
 import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.stream.Stream;
 
 import jdk.internal.access.JavaLangInvokeAccess;
 import jdk.internal.access.SharedSecrets;
+import jdk.internal.value.LayoutIteration;
 import sun.invoke.util.Wrapper;
 
 import static java.lang.invoke.MethodHandles.constant;
@@ -92,19 +94,12 @@ static class MethodHandleBuilder {
 
         static Stream<MethodHandle> getterStream(Class<?> type, Comparator<MethodHandle> comparator) {
             // filter static fields
-            Stream<MethodHandle> s = Arrays.stream(type.getDeclaredFields())
-                .filter(f -> !Modifier.isStatic(f.getModifiers()))
-                .map(f -> {
-                    try {
-                        return JLIA.unreflectField(f, false);
-                    } catch (IllegalAccessException e) {
-                        throw newLinkageError(e);
-                    }
-                });
+            List<MethodHandle> mhs = LayoutIteration.ELEMENTS.get(type);
             if (comparator != null) {
-                s = s.sorted(comparator);
+                mhs = new ArrayList<>(mhs);
+                mhs.sort(comparator);
             }
-            return s;
+            return mhs.stream();
         }
 
         static MethodHandle hashCodeForType(Class<?> type) {
@@ -141,13 +136,11 @@ static Class<?> fieldType(MethodHandle getter) {
         }
 
         private static List<Class<?>> valueTypeFields(Class<?> type) {
-            List<Class<?>> result = new ArrayList<>();
-            Arrays.stream(type.getDeclaredFields())
-                  .filter(f -> !Modifier.isStatic(f.getModifiers()))
-                  .map(f -> f.getType())
-                  .filter(ft -> ft.isValue() && !result.contains(ft))
-                  .forEach(result::add);
-            return result;
+            return LayoutIteration.ELEMENTS.get(type).stream()
+                    .<Class<?>>map(mh -> mh.type().returnType())
+                    .filter(Class::isValue)
+                    .distinct()
+                    .toList();
         }
 
         /*

src/java.base/share/classes/jdk/internal/access/JavaLangInvokeAccess.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2025, 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
@@ -28,7 +28,6 @@
 import jdk.internal.foreign.abi.NativeEntryPoint;
 
 import java.lang.invoke.MethodHandle;
-import java.lang.invoke.MethodHandles.Lookup;
 import java.lang.invoke.MethodType;
 import java.lang.invoke.VarHandle;
 import java.lang.reflect.Constructor;
@@ -176,4 +175,14 @@ public interface JavaLangInvokeAccess {
      * This method should only be used by ReflectionFactory::newConstructorForSerialization.
      */
     MethodHandle serializableConstructor(Class<?> decl, Constructor<?> ctorToCall) throws IllegalAccessException;
+
+    /**
+     * Asserts a method handle to be another type without the conversion adaptions.
+     * Useful to avoid many redundant casts.
+     *
+     * @param original original MH
+     * @param assertedType the asserted type the origina MH can execute as
+     * @return the cheap view without extra adaptions
+     */
+    MethodHandle assertAsType(MethodHandle original, MethodType assertedType);
 }

src/java.base/share/classes/jdk/internal/value/LayoutIteration.java

@@ -0,0 +1,167 @@
+/*
+ * Copyright (c) 2025, 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.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * 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.
+ */
+
+package jdk.internal.value;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+import java.util.ArrayList;
+import java.util.List;
+
+import jdk.internal.access.JavaLangInvokeAccess;
+import jdk.internal.access.SharedSecrets;
+import jdk.internal.misc.Unsafe;
+import sun.invoke.util.Wrapper;
+
+/**
+ * Iterates the layout elements of a value type.
+ * <p>
+ * In the long run, we should do this:
+ * Iterate the layout, create a mask masking bytes used by Object/abstract value
+ * class reference fields.  Do a byte-wise compare and get the mask of value
+ * mismatch; if the mask's all clear, fine; if the mask has bits beyond our
+ * mask, fail; otherwise, compare reference fields indicated by the mismatch
+ * mask. There may be paddings to ignore, too, depends...
+ */
+public final class LayoutIteration {
+    // Initializer in static initializers below, order dependent
+    public static final ClassValue<List<MethodHandle>> ELEMENTS;
+
+    /**
+     * {@return a list of method handles accessing the basic elements}
+     * Basic elements are 8 primitives and pointers (to identity or value objects).
+     * Primitives and pointers are distinguished by the MH return types.
+     * The MH types are {@code flatType -> fieldType}.
+     *
+     * @param flatType the class that has a flat layout
+     * @return the accessors
+     * @throws IllegalArgumentException if argument has no flat layout
+     */
+    public static List<MethodHandle> computeElementGetters(Class<?> flatType) {
+        if (!canHaveFlatLayout(flatType))
+            throw new IllegalArgumentException(flatType + " cannot be flat");
+        var sink = new Sink(flatType);
+        iterateFields(U.valueHeaderSize(flatType), flatType, sink);
+        return List.copyOf(sink.getters);
+    }
+
+    // Ensures the given class has a potential a flat layout
+    private static boolean canHaveFlatLayout(Class<?> flatType) {
+        return flatType.isValue() && Modifier.isFinal(flatType.getModifiers());
+    }
+
+    private static final class Sink {
+        final Class<?> receiverType;
+        final List<MethodHandle> getters = new ArrayList<>();
+
+        Sink(Class<?> receiverType) {
+            this.receiverType = receiverType;
+        }
+
+        void accept(long offsetNoHeader, Class<?> itemType) {
+            Wrapper w = itemType.isPrimitive() ? Wrapper.forPrimitiveType(itemType) : Wrapper.OBJECT;
+            var mh = MethodHandles.insertArguments(FIELD_GETTERS.get(w.ordinal()), 1, offsetNoHeader);
+            assert mh.type() == MethodType.methodType(w.primitiveType(), Object.class);
+            mh = JLIA.assertAsType(mh, MethodType.methodType(itemType, receiverType));
+            getters.add(mh);
+        }
+    }
+
+    // Sink is good for one to many mappings
+    private static void iterateFields(long enclosingOffset, Class<?> currentClass, Sink sink) {
+        assert canHaveFlatLayout(currentClass) : currentClass + " cannot be flat";
+        long memberOffsetDelta = enclosingOffset - U.valueHeaderSize(currentClass);
+        for (Field f : currentClass.getDeclaredFields()) {
+            if (Modifier.isStatic(f.getModifiers()))
+                continue;
+            var type = f.getType();
+            long memberOffset = U.objectFieldOffset(f) + memberOffsetDelta;
+            if (!U.isFlatField(f)) {
+                sink.accept(memberOffset, type);
+            } else {
+                iterateFields(memberOffset, type, sink);
+            }
+        }
+    }
+
+    private static boolean getBoolean(Object o, long offset) {
+        return U.getBoolean(o, offset);
+    }
+    private static byte getByte(Object o, long offset) {
+        return U.getByte(o, offset);
+    }
+    private static short getShort(Object o, long offset) {
+        return U.getShort(o, offset);
+    }
+    private static char getCharacter(Object o, long offset) {
+        return U.getChar(o, offset);
+    }
+    private static int getInteger(Object o, long offset) {
+        return U.getInt(o, offset);
+    }
+    private static long getLong(Object o, long offset) {
+        return U.getLong(o, offset);
+    }
+    private static float getFloat(Object o, long offset) {
+        return U.getFloat(o, offset);
+    }
+    private static double getDouble(Object o, long offset) {
+        return U.getDouble(o, offset);
+    }
+    public static Object getObject(Object o, long offset) {
+        return U.getReference(o, offset);
+    }
+
+    private static final Unsafe U = Unsafe.getUnsafe();
+    private static final JavaLangInvokeAccess JLIA = SharedSecrets.getJavaLangInvokeAccess();
+    private static final List<MethodHandle> FIELD_GETTERS;
+    static {
+        MethodHandle[] fieldGetters = new MethodHandle[9];
+        var lookup = MethodHandles.lookup();
+        var type = MethodType.methodType(void.class, Object.class, long.class);
+        try {
+            for (Wrapper w : Wrapper.values()) {
+                if (w != Wrapper.VOID) {
+                    fieldGetters[w.ordinal()] = lookup.findStatic(LayoutIteration.class,
+                            "get" + w.wrapperSimpleName(), type.changeReturnType(w.primitiveType()));
+                }
+            }
+        } catch (ReflectiveOperationException ex) {
+            throw new ExceptionInInitializerError(ex);
+        }
+        FIELD_GETTERS = List.of(fieldGetters);
+        ELEMENTS = new ClassValue<>() {
+            @Override
+            protected List<MethodHandle> computeValue(Class<?> type) {
+                return computeElementGetters(type);
+            }
+        };
+    }
+
+    private LayoutIteration() {}
+}

test/jdk/valhalla/valuetypes/LayoutIterationTest.java

@@ -0,0 +1,89 @@
+/*
+ * Copyright (c) 2025, 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.
+ */
+
+
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import jdk.internal.value.LayoutIteration;
+import jdk.internal.vm.annotation.ImplicitlyConstructible;
+import jdk.internal.vm.annotation.LooselyConsistentValue;
+import jdk.internal.vm.annotation.NullRestricted;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/*
+ * @test
+ * @summary test LayoutIteration
+ * @enablePreview
+ * @modules java.base/jdk.internal.vm.annotation
+ *          java.base/jdk.internal.value
+ * @run junit/othervm LayoutIterationTest
+ */
+class LayoutIterationTest {
+
+    @LooselyConsistentValue
+    @ImplicitlyConstructible
+    static value class One {
+        int a;
+        short b;
+
+        One(int a, short b) {
+            this.a = a;
+            this.b = b;
+        }
+    }
+
+    @LooselyConsistentValue
+    static value class Two {
+        @NullRestricted
+        One one = new One(5, (short) 3);
+        One anotherOne = new One(4, (short) 2);
+        long l = 5L;
+    }
+
+    @Test
+    void test() {
+        Two t = new Two();
+        Set<Class<?>> classes = LayoutIteration.computeElementGetters(One.class).stream()
+                .map(mh -> mh.type().returnType()).collect(Collectors.toSet());
+        assertEquals(Set.of(int.class, short.class), classes);
+        Map<Class<?>, Object> values = LayoutIteration.computeElementGetters(Two.class).stream()
+                .collect(Collectors.toMap(mh -> mh.type().returnType(), mh -> {
+                    try {
+                        return (Object) mh.invoke(t);
+                    } catch (Throwable ex) {
+                        return Assertions.fail(ex);
+                    }
+                }));
+        assertEquals(Map.of(
+                int.class, t.one.a,
+                short.class, t.one.b,
+                One.class, t.anotherOne,
+                long.class, t.l
+        ), values);
+    }
+}