8337066: Repeated call of StringBuffer.reverse with double byte string returns wrong result

Reviewed-by: kvn, thartmann

src/hotspot/share/opto/gcm.cpp

@@ -746,6 +746,21 @@ Block* PhaseCFG::insert_anti_dependences(Block* LCA, Node* load, bool verify) {
   // The anti-dependence constraints apply only to the fringe of this tree.
 
   Node* initial_mem = load->in(MemNode::Memory);
+
+  // We don't optimize the memory graph for pinned loads, so we may need to raise the
+  // root of our search tree through the corresponding slices of MergeMem nodes to
+  // get to the node that really creates the memory state for this slice.
+  if (load_alias_idx >= Compile::AliasIdxRaw) {
+    while (initial_mem->is_MergeMem()) {
+      MergeMemNode* mm = initial_mem->as_MergeMem();
+      Node* p = mm->memory_at(load_alias_idx);
+      if (p != mm->base_memory()) {
+        initial_mem = p;
+      } else {
+        break;
+      }
+    }
+  }
   worklist_def_use_mem_states.push(nullptr, initial_mem);
   while (worklist_def_use_mem_states.is_nonempty()) {
     // Examine a nearby store to see if it might interfere with our load.

test/hotspot/jtreg/compiler/controldependency/TestAntiDependencyForPinnedLoads.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2024, 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 8337066
+ * @summary Test that MergeMem is skipped when looking for stores
+ * @run main/othervm -Xbatch -XX:-TieredCompilation
+ *                   -XX:CompileCommand=compileonly,java.lang.StringUTF16::reverse
+ *                   compiler.controldependency.TestAntiDependencyForPinnedLoads
+ */
+
+package compiler.controldependency;
+
+public class TestAntiDependencyForPinnedLoads {
+    public static void main(String[] args) {
+        for(int i = 0; i < 50_000; i++) {
+            String str = "YYYY年MM月DD日";
+            StringBuffer strBuffer = new StringBuffer(str);
+            String revStr = strBuffer.reverse().toString();
+            if (!revStr.equals("日DD月MM年YYYY")) throw new InternalError("FAIL");
+        }
+    }
+}