8160821: VarHandle accesses are penalized when argument conversion is required

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

@@ -622,6 +622,8 @@ static boolean profileBoolean(boolean result, int[] counters) {
     }
 
     // Intrinsified by C2. Returns true if obj is a compile-time constant.
+    // Note that a non-constant value may be subsequently promoted to a constant,
+    // so a false return value does not indicate obj is definitely not a constant.
     @Hidden
     @jdk.internal.vm.annotation.IntrinsicCandidate
     static boolean isCompileConstant(Object obj) {

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 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
@@ -2017,14 +2017,49 @@ static final class AccessDescriptor {
         final int type;
         final int mode;
 
-        public AccessDescriptor(MethodType symbolicMethodType, int type, int mode) {
+        // Adaption mechanism to reduce overhead for non-exact access.
+        // This heuristic assumes that each sigpoly VH call site usually sees
+        // exactly one VarHandle instance.  Each sigpoly VH call site already
+        // has a dedicated AccessDescriptor.
+        // (See MethodHandleNatives::varHandleOperationLinkerMethod)
+        // However, for correctness, we must verify the incoming VarHandle;
+        // adaptedMethodHandle may be inlined by different callers.
+        // In the long run, we wish to put a specific-type invoker that converts
+        // from one fixed type (symbolicMethodTypeInvoker) to another (the
+        // invocation type of the underlying MemberName, or MH for indirect VH),
+        // perform a foldable lookup with a hash table, and hope C2 inline it
+        // all.
+
+        // Object indirection is the only way to ensure the vh and mh are not
+        // from two writes (they must not be tearable)
+        private record Adaption(VarHandle vh, MethodHandle mh) {}
+        private @Stable Adaption adaption;
+
+        AccessDescriptor(MethodType symbolicMethodType, int type, int mode) {
             this.symbolicMethodTypeExact = symbolicMethodType;
             this.symbolicMethodTypeErased = symbolicMethodType.erase();
             this.symbolicMethodTypeInvoker = symbolicMethodType.insertParameterTypes(0, VarHandle.class);
             this.returnType = symbolicMethodType.returnType();
             this.type = type;
             this.mode = mode;
         }
+
+        @ForceInline
+        MethodHandle adaptedMethodHandle(VarHandle vh) {
+            var cache = adaption;
+            if (cache != null && cache.vh == vh) {
+                return cache.mh;
+            }
+
+            var mh = vh.getMethodHandle(mode).asType(symbolicMethodTypeInvoker);
+            if (cache == null) {
+                // Reduce costly object allocation - if our assumption stands,
+                // the first adaption works, and we don't want allocations for
+                // every VH invocation.
+                adaption = new Adaption(vh, mh);
+            }
+            return mh;
+        }
     }
 
     /**

test/hotspot/jtreg/compiler/c2/irTests/TestGetAndAdd.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2023, 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
@@ -29,7 +29,7 @@
 
 /*
  * @test
- * bug 8308444
+ * @bug 8308444
  * @summary verify that the correct node is matched for atomic getAndAdd
  * @requires os.simpleArch == "x64"
  * @requires vm.compiler2.enabled

test/hotspot/jtreg/compiler/c2/irTests/constantFold/VarHandleMismatchedTypeFold.java

@@ -0,0 +1,79 @@
+/*
+ * 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.
+ */
+
+package compiler.c2.irTests.constantFold;
+
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
+
+import compiler.lib.ir_framework.Check;
+import compiler.lib.ir_framework.IR;
+import compiler.lib.ir_framework.IRNode;
+import compiler.lib.ir_framework.Run;
+import compiler.lib.ir_framework.Test;
+import compiler.lib.ir_framework.TestFramework;
+
+/*
+ * @test
+ * @bug 8160821
+ * @summary Verify constant folding is possible for mismatched VarHandle access
+ * @library /test/lib /
+ * @requires vm.compiler2.enabled
+ * @run driver compiler.c2.irTests.constantFold.VarHandleMismatchedTypeFold
+ */
+public class VarHandleMismatchedTypeFold {
+
+    public static void main(String[] args) {
+        TestFramework.runWithFlags(
+            "-XX:+UnlockExperimentalVMOptions"
+        );
+    }
+
+    static final int a = 5;
+
+    static final VarHandle vh;
+
+    static {
+        try {
+            vh = MethodHandles.lookup().findStaticVarHandle(VarHandleMismatchedTypeFold.class,
+                    "a", int.class);
+        } catch (ReflectiveOperationException e) {
+            throw new ExceptionInInitializerError(e);
+        }
+    }
+
+    @Test
+    @IR(failOn = {IRNode.ADD_L, IRNode.LOAD_L})
+    public long testSum() {
+        return 2L + (long) vh.get();
+    }
+
+    @Check(test = "testSum")
+    public void runTestSum() {
+        long sum = testSum();
+        if (sum != 2L + 5L) {
+            throw new IllegalStateException("Failed, unexpected sum " + sum);
+        }
+    }
+
+}

test/jdk/java/lang/invoke/VarHandles/PolymorphicCallSiteInlineTest.java

@@ -0,0 +1,105 @@
+/*
+ * 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.
+ */
+
+/*
+ * @test
+ * @bug 8160821
+ * @summary Ensures a polymorphic call site with non-exact invocation won't
+ *          be incorrectly inlined/optimized
+ * @requires vm.compiler2.enabled
+ * @run main/othervm -XX:CompileCommand=PrintCompilation,Main::*
+ *                   -XX:CompileCommand=dontinline,Main::payload*
+ *                   -Xbatch
+ *                   PolymorphicCallSiteInlineTest
+ */
+
+import java.lang.invoke.*;
+import java.util.concurrent.CountDownLatch;
+
+public class PolymorphicCallSiteInlineTest {
+
+    // C2 should inline m into payload1/payload2 in this many runs
+    static final int RUNS = 0x10000;
+
+    static final int X = 0;
+    static final long Y = 0L;
+
+    static final VarHandle VH_X;
+    static final VarHandle VH_Y;
+
+    static {
+        try {
+            var lookup = MethodHandles.lookup();
+            VH_X = lookup.findStaticVarHandle(PolymorphicCallSiteInlineTest.class, "X", int.class);
+            VH_Y = lookup.findStaticVarHandle(PolymorphicCallSiteInlineTest.class, "Y", long.class);
+        } catch (ReflectiveOperationException e) {
+            throw new ExceptionInInitializerError(e);
+        }
+    };
+
+    public static void main(String[] args) {
+
+        CountDownLatch latch = new CountDownLatch(2);
+
+        Thread.ofPlatform().start(() -> {
+            latch.countDown();
+            try {
+                latch.await();
+            } catch (InterruptedException ex) {
+                throw new RuntimeException(ex);
+            }
+            System.out.println("T1 running");
+            for (int i = 0; i < RUNS; i++) {
+                payload1();
+            }
+        });
+
+        Thread.ofPlatform().start(() -> {
+            latch.countDown();
+            try {
+                latch.await();
+            } catch (InterruptedException ex) {
+                throw new RuntimeException(ex);
+            }
+            System.out.println("T2 running");
+            for (int i = 0; i < RUNS; i++) {
+                payload2();
+            }
+        });
+    }
+
+    public static int payload1() {
+        return (int) m(VH_X);
+    }
+
+    public static long payload2() {
+        return (long) m(VH_Y);
+    }
+
+    public static Object m(VarHandle vh) {
+        // This is a polymorphic site that sees many VarHandle, but each VH
+        // is considered "constant" when inlined into payload1/payload2
+        // payload1/payload2 will throw exceptions if the incorrect VH gets inlined
+        return vh.get();
+    }
+}

test/micro/org/openjdk/bench/java/lang/foreign/VarHandleExact.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 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
@@ -74,16 +74,21 @@ public void tearDown() {
 
     @Benchmark
     public void exact_exactInvocation() {
-        exact.set(data, (long) 0, 42);
+        var _ = (int) exact.getAndAdd(data, (long) 0, 42);
     }
 
     @Benchmark
     public void generic_genericInvocation() {
-        generic.set(data, 0, 42);
+        generic.getAndAdd(data, 0, 42);
+    }
+
+    @Benchmark
+    public void generic_returnDroppingInvocation() {
+        generic.getAndAdd(data, (long) 0, 42);
     }
 
     @Benchmark
     public void generic_exactInvocation() {
-        generic.set(data, (long) 0, 42);
+        var _ = (int) generic.getAndAdd(data, (long) 0, 42);
     }
 }

test/micro/org/openjdk/bench/java/lang/invoke/VarHandleExact.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 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
@@ -69,16 +69,21 @@ public void setup() {
 
     @Benchmark
     public void exact_exactInvocation() {
-        exact.set(data, (long) 42);
+        var _ = (long) exact.getAndAdd(data, (long) 42);
     }
 
     @Benchmark
     public void generic_genericInvocation() {
-        generic.set(data, 42);
+        generic.getAndAdd(data, 42);
+    }
+
+    @Benchmark
+    public void generic_returnDroppingInvocation() {
+        generic.getAndAdd(data, (long) 42);
     }
 
     @Benchmark
     public void generic_exactInvocation() {
-        generic.set(data, (long) 42);
+        var _ = (long) generic.getAndAdd(data, (long) 42);
     }
 }