8262891: Compiler implementation for Pattern Matching for switch (Preview)

Co-authored-by: Brian Goetz <briangoetz@openjdk.org>
Co-authored-by: Mandy Chung <mchung@openjdk.org>
Co-authored-by: Jan Lahoda <jlahoda@openjdk.org>
Reviewed-by: mcimadamore, forax, godin, psandoz, mchung

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

@@ -0,0 +1,170 @@
+/*
+ * Copyright (c) 2017, 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.  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 java.lang.runtime;
+
+import java.lang.invoke.CallSite;
+import java.lang.invoke.ConstantCallSite;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.util.Arrays;
+import java.util.Objects;
+import java.util.stream.Stream;
+
+import jdk.internal.javac.PreviewFeature;
+
+import static java.util.Objects.requireNonNull;
+
+/**
+ * Bootstrap methods for linking {@code invokedynamic} call sites that implement
+ * the selection functionality of the {@code switch} statement.  The bootstraps
+ * take additional static arguments corresponding to the {@code case} labels
+ * of the {@code switch}, implicitly numbered sequentially from {@code [0..N)}.
+ *
+ * @since 17
+ */
+@PreviewFeature(feature=PreviewFeature.Feature.SWITCH_PATTERN_MATCHING)
+public class SwitchBootstraps {
+
+    private SwitchBootstraps() {}
+
+    private static final MethodHandles.Lookup LOOKUP = MethodHandles.lookup();
+
+    private static final MethodHandle DO_SWITCH;
+
+    static {
+        try {
+            DO_SWITCH = LOOKUP.findStatic(SwitchBootstraps.class, "doSwitch",
+                                           MethodType.methodType(int.class, Object.class, int.class, Object[].class));
+        }
+        catch (ReflectiveOperationException e) {
+            throw new ExceptionInInitializerError(e);
+        }
+    }
+
+    /**
+     * Bootstrap method for linking an {@code invokedynamic} call site that
+     * implements a {@code switch} on a target of a reference type.  The static
+     * arguments are an array of case labels which must be non-null and of type
+     * {@code String} or {@code Integer} or {@code Class}.
+     * <p>
+     * The type of the returned {@code CallSite}'s method handle will have
+     * a return type of {@code int}.   It has two parameters: the first argument
+     * will be an {@code Object} instance ({@code target}) and the second
+     * will be {@code int} ({@code restart}).
+     * <p>
+     * If the {@code target} is {@code null}, then the method of the call site
+     * returns {@literal -1}.
+     * <p>
+     * If the {@code target} is not {@code null}, then the method of the call site
+     * returns the index of the first element in the {@code labels} array starting from
+     * the {@code restart} index matching one of the following conditions:
+     * <ul>
+     *   <li>the element is of type {@code Class} that is assignable
+     *       from the target's class; or</li>
+     *   <li>the element is of type {@code String} or {@code Integer} and
+     *       equals to the target.</li>
+     * </ul>
+     * <p>
+     * If no element in the {@code labels} array matches the target, then
+     * the method of the call site return the length of the {@code labels} array.
+     *
+     * @param lookup Represents a lookup context with the accessibility
+     *               privileges of the caller.  When used with {@code invokedynamic},
+     *               this is stacked automatically by the VM.
+     * @param invocationName unused
+     * @param invocationType The invocation type of the {@code CallSite} with two parameters,
+     *                       a reference type, an {@code int}, and {@code int} as a return type.
+     * @param labels case labels - {@code String} and {@code Integer} constants
+     *               and {@code Class} instances, in any combination
+     * @return a {@code CallSite} returning the first matching element as described above
+     *
+     * @throws NullPointerException if any argument is {@code null}
+     * @throws IllegalArgumentException if any element in the labels array is null, if the
+     * invocation type is not not a method type of first parameter of a reference type,
+     * second parameter of type {@code int} and with {@code int} as its return type,
+     * or if {@code labels} contains an element that is not of type {@code String},
+     * {@code Integer} or {@code Class}.
+     * @throws Throwable if there is any error linking the call site
+     * @jvms 4.4.6 The CONSTANT_NameAndType_info Structure
+     * @jvms 4.4.10 The CONSTANT_Dynamic_info and CONSTANT_InvokeDynamic_info Structures
+     */
+    public static CallSite typeSwitch(MethodHandles.Lookup lookup,
+                                      String invocationName,
+                                      MethodType invocationType,
+                                      Object... labels) throws Throwable {
+        if (invocationType.parameterCount() != 2
+            || (!invocationType.returnType().equals(int.class))
+            || invocationType.parameterType(0).isPrimitive()
+            || !invocationType.parameterType(1).equals(int.class))
+            throw new IllegalArgumentException("Illegal invocation type " + invocationType);
+        requireNonNull(labels);
+
+        labels = labels.clone();
+        Stream.of(labels).forEach(SwitchBootstraps::verifyLabel);
+
+        MethodHandle target = MethodHandles.insertArguments(DO_SWITCH, 2, (Object) labels);
+        return new ConstantCallSite(target);
+    }
+
+    private static void verifyLabel(Object label) {
+        if (label == null) {
+            throw new IllegalArgumentException("null label found");
+        }
+        Class<?> labelClass = label.getClass();
+        if (labelClass != Class.class &&
+            labelClass != String.class &&
+            labelClass != Integer.class) {
+            throw new IllegalArgumentException("label with illegal type found: " + label.getClass());
+        }
+    }
+
+    private static int doSwitch(Object target, int startIndex, Object[] labels) {
+        if (target == null)
+            return -1;
+
+        // Dumbest possible strategy
+        Class<?> targetClass = target.getClass();
+        for (int i = startIndex; i < labels.length; i++) {
+            Object label = labels[i];
+            if (label instanceof Class<?> c) {
+                if (c.isAssignableFrom(targetClass))
+                    return i;
+            } else if (label instanceof Integer constant) {
+                if (target instanceof Number input && constant.intValue() == input.intValue()) {
+                    return i;
+                } else if (target instanceof Character input && constant.intValue() == input.charValue()) {
+                    return i;
+                }
+            } else if (label.equals(target)) {
+                return i;
+            }
+        }
+
+        return labels.length;
+    }
+
+}