[GR-78804] Support string outlining.

substratevm/CHANGELOG.md

@@ -4,6 +4,7 @@ This changelog summarizes major changes to GraalVM Native Image.
 
 ## GraalVM 25.4 (Internal Version 25.4.4)
 * (GR-78784) Default to optional identity hash code fields with SerialGC. Few objects need one, and this optimization adds them during garbage collection. It can be disabled with `-H:-OptionalIdentityHashCodes`.
+* (GR-78804) Added outlining for StringBuilder/StringBuffer append sequences and invokedynamic string concatenations. This reduces the binary size of native executables.
 
 ## GraalVM 25.3 (Internal Version 25.3.4.1)
 * (GR-77137) Added `SubstratePriorityInliningPhase` to leverage the new priority inliner added to the compiler suite.

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/sboutlining/OutlinedSBMethodHolder.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2022, 2026, 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 com.oracle.svm.core.sboutlining;
+
+import com.oracle.svm.guest.staging.jdk.InternalVMMethod;
+
+/**
+ * Declaring class for synthetic string aggregation methods.
+ *
+ * <p>
+ * The methods do not have Java declarations in this class. During analysis,
+ * Native Image creates synthetic methods and registers them as methods of this type during
+ * analysis. Transformed graphs can then refer to the generated implementations through ordinary
+ * static calls. The holder itself has no instances or runtime state.
+ */
+@InternalVMMethod
+public final class OutlinedSBMethodHolder {
+    private OutlinedSBMethodHolder() {
+    }
+}