8350118: Simplify the layout access VarHandle

Reviewed-by: mcimadamore, jvernee, erikj

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

@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2019, 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 java.lang.invoke;
+
+import java.lang.foreign.MemoryLayout;
+import java.lang.foreign.MemorySegment;
+import java.util.Objects;
+
+import jdk.internal.foreign.AbstractMemorySegmentImpl;
+import jdk.internal.misc.ScopedMemoryAccess;
+import jdk.internal.vm.annotation.ForceInline;
+
+/**
+ * A var handle that accesses primitive values in a memory segment.
+ */
+final class SegmentVarHandle extends VarHandle {
+
+    // Common implementation fields for the VarForms
+    static final boolean BE = MethodHandleStatics.UNSAFE.isBigEndian();
+    static final ScopedMemoryAccess SCOPED_MEMORY_ACCESS = ScopedMemoryAccess.getScopedMemoryAccess();
+
+    /** endianness **/
+    final boolean be;
+    /** The layout the accessed segment must be compatible with. */
+    final MemoryLayout enclosing;
+    /** The offset value, if is constant. vform decides if offset is constant or variable. */
+    final long offset;
+
+    SegmentVarHandle(VarForm form, boolean be, MemoryLayout enclosing, long offset, boolean exact) {
+        super(form, exact);
+        this.be = be;
+        this.enclosing = enclosing;
+        this.offset = offset;
+    }
+
+    @Override
+    final MethodType accessModeTypeUncached(VarHandle.AccessType accessType) {
+        var getType = vform.methodType_table[0]; // erased, but our value type is erase-compatible
+        return getType.parameterCount() == 2
+                ? accessType.accessModeType(MemorySegment.class, getType.returnType(), long.class)
+                : accessType.accessModeType(MemorySegment.class, getType.returnType(), long.class, long.class);
+    }
+
+    @Override
+    public SegmentVarHandle withInvokeExactBehavior() {
+        return hasInvokeExactBehavior() ?
+                this :
+                new SegmentVarHandle(vform, be, enclosing, offset, true);
+    }
+
+    @Override
+    public SegmentVarHandle withInvokeBehavior() {
+        return !hasInvokeExactBehavior() ?
+                this :
+                new SegmentVarHandle(vform, be, enclosing, offset, false);
+    }
+
+    // Common implementation methods for the VarForms
+
+    @ForceInline
+    static long offset(AbstractMemorySegmentImpl bb, long base, long offset) {
+        long segment_base = bb.unsafeGetOffset();
+        return segment_base + base + offset;
+    }
+
+    @ForceInline
+    AbstractMemorySegmentImpl checkSegment(Object obb, long base, boolean ro) {
+        AbstractMemorySegmentImpl oo = (AbstractMemorySegmentImpl) Objects.requireNonNull(obb);
+        oo.checkEnclosingLayout(base, this.enclosing, ro);
+        return oo;
+    }
+}