8319784: VM crash during heap dump after JDK-8287061

Reviewed-by: kvn, thartmann, shade

src/hotspot/share/code/debugInfo.cpp

@@ -265,6 +265,14 @@ ObjectValue* ObjectMergeValue::select(frame& fr, RegisterMap& reg_map) {
   }
 }
 
+Handle ObjectMergeValue::value() const {
+  if (_selected != nullptr) {
+    return _selected->value();
+  } else {
+    return Handle();
+  }
+}
+
 void ObjectMergeValue::read_object(DebugInfoReadStream* stream) {
   _selector = read_from(stream);
   _merge_pointer = read_from(stream);

src/hotspot/share/code/debugInfo.hpp

@@ -232,7 +232,7 @@ class ObjectMergeValue: public ObjectValue {
   ScopeValue*                 field_at(int i) const           { ShouldNotReachHere(); return nullptr; }
   int                         field_size()                    { ShouldNotReachHere(); return -1; }
 
-  Handle                      value() const                   { assert(_selected != nullptr, "Should call select() first."); return _selected->value(); }
+  Handle                      value() const;
   void                        set_value(oop value)            { assert(_selected != nullptr, "Should call select() first."); _selected->set_value(value); }
 
   // Serialization of debugging information

test/hotspot/jtreg/compiler/c2/TestReduceAllocationAndHeapDump.java

@@ -0,0 +1,110 @@
+/*
+ * Copyright (c) 2023, 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 8319784
+ * @summary Check that the JVM is able to dump the heap even when there are ReduceAllocationMerge in the scope.
+ * @library /test/lib /
+ * @run main/othervm compiler.c2.TestReduceAllocationAndHeapDump
+ */
+
+package compiler.c2;
+
+import java.io.File;
+import jdk.test.lib.process.OutputAnalyzer;
+import jdk.test.lib.process.ProcessTools;
+
+public class TestReduceAllocationAndHeapDump {
+    public static void main(String[] args) throws Exception {
+        File dumpDirectory = new File("dumps");
+
+        try {
+            if (!dumpDirectory.exists()) {
+                dumpDirectory.mkdir();
+            }
+
+            String[] dumperArgs = {
+                "-server",
+                "-XX:CompileThresholdScaling=0.01",
+                "-XX:+HeapDumpAfterFullGC",
+                "-XX:HeapDumpPath=" + dumpDirectory.getAbsolutePath(),
+                "-XX:CompileCommand=compileonly,compiler.c2.HeapDumper::testIt",
+                "-XX:CompileCommand=exclude,compiler.c2.HeapDumper::dummy",
+                HeapDumper.class.getName()
+            };
+
+            ProcessBuilder pb = ProcessTools.createLimitedTestJavaProcessBuilder(dumperArgs);
+            Process p = pb.start();
+            OutputAnalyzer out = new OutputAnalyzer(p);
+
+            if (out.getExitValue() != 0) {
+                throw new IllegalStateException("Subprocess finished with non-zero exit code.");
+            }
+        } finally {
+            File[] files = dumpDirectory.listFiles((dir, name) -> name.endsWith(".hprof"));
+
+            for (File file : files) {
+                System.out.println("Deleting " + file.getAbsolutePath());
+                file.delete();
+            }
+        }
+    }
+}
+
+class HeapDumper {
+    public static Point p = new Point(0);
+
+    public static void main(String[] args) throws Exception {
+        for (int i = 0; i < 5000; i++) {
+            testIt(i);
+        }
+    }
+
+    public static void testIt(int i) throws Exception {
+        Point p = (i % 2 == 0) ? new Point(i) : new Point(i);
+
+        dummy(i);
+
+        if (i < 5000) {
+            dummy(i);
+        } else {
+            dummy(p.x + i);
+        }
+    }
+
+    public static void dummy(int x) {
+        if (x > 4900) {
+            System.gc();
+        }
+    }
+}
+
+// Helper class
+class Point {
+    public int x;
+
+    public Point(int xx) {
+        this.x = xx;
+    }
+}