8223923: C2: Missing interference with mismatched unsafe accesses

Reviewed-by: thartmann

src/hotspot/share/opto/memnode.cpp

@@ -596,7 +596,7 @@ Node* LoadNode::find_previous_arraycopy(PhaseTransform* phase, Node* ld_alloc, N
 
 ArrayCopyNode* MemNode::find_array_copy_clone(PhaseTransform* phase, Node* ld_alloc, Node* mem) const {
   if (mem->is_Proj() && mem->in(0) != NULL && (mem->in(0)->Opcode() == Op_MemBarStoreStore ||
-                                                 mem->in(0)->Opcode() == Op_MemBarCPUOrder)) {
+                                               mem->in(0)->Opcode() == Op_MemBarCPUOrder)) {
     if (ld_alloc != NULL) {
       // Check if there is an array copy for a clone
       Node* mb = mem->in(0);
@@ -1061,7 +1061,6 @@ Node* MemNode::can_see_stored_value(Node* st, PhaseTransform* phase) const {
   // This is more general than load from boxing objects.
   if (skip_through_membars(atp, tp, phase->C->eliminate_boxing())) {
     uint alias_idx = atp->index();
-    bool final = !atp->is_rewritable();
     Node* result = NULL;
     Node* current = st;
     // Skip through chains of MemBarNodes checking the MergeMems for
@@ -1069,17 +1068,19 @@ Node* MemNode::can_see_stored_value(Node* st, PhaseTransform* phase) const {
     // kind of node is encountered.  Loads from final memory can skip
     // through any kind of MemBar but normal loads shouldn't skip
     // through MemBarAcquire since the could allow them to move out of
-    // a synchronized region.
+    // a synchronized region. It is not safe to step over MemBarCPUOrder,
+    // because alias info above them may be inaccurate (e.g., due to
+    // mixed/mismatched unsafe accesses).
+    bool is_final_mem = !atp->is_rewritable();
     while (current->is_Proj()) {
       int opc = current->in(0)->Opcode();
-      if ((final && (opc == Op_MemBarAcquire ||
+      if ((is_final_mem && (opc == Op_MemBarAcquire ||
-                     opc == Op_MemBarAcquireLock ||
+                            opc == Op_MemBarAcquireLock ||
-                     opc == Op_LoadFence)) ||
+                            opc == Op_LoadFence)) ||
           opc == Op_MemBarRelease ||
           opc == Op_StoreFence ||
           opc == Op_MemBarReleaseLock ||
-          opc == Op_MemBarStoreStore ||
+          opc == Op_MemBarStoreStore) {
-          opc == Op_MemBarCPUOrder) {
         Node* mem = current->in(0)->in(TypeFunc::Memory);
         if (mem->is_MergeMem()) {
           MergeMemNode* merge = mem->as_MergeMem();

test/hotspot/jtreg/compiler/unsafe/MismatchedUnsafeAccessTest.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2021, 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 8223923
+ * @modules java.base/jdk.internal.misc
+ * @run main/othervm -Xbatch compiler.unsafe.MismatchedUnsafeAccessTest
+ */
+package compiler.unsafe;
+
+import jdk.internal.misc.Unsafe;
+
+public class MismatchedUnsafeAccessTest {
+    private static final Unsafe UNSAFE = Unsafe.getUnsafe();
+
+    public static class Test {
+        public int x = 0;
+        public int y = 0;
+
+        public static final long offsetX;
+        public static final long offsetY;
+
+        static {
+            try {
+                offsetX = UNSAFE.objectFieldOffset(Test.class.getField("x"));
+                offsetY = UNSAFE.objectFieldOffset(Test.class.getField("y"));
+            } catch (NoSuchFieldException e) {
+                throw new InternalError(e);
+            }
+            // Validate offsets
+            if (offsetX >= offsetY || offsetY - offsetX != 4) {
+                throw new InternalError("Wrong offsets: " + offsetX + " " + offsetY);
+            }
+        }
+    }
+
+    public static int test(long l) {
+        Test a = new Test();
+        UNSAFE.putLong(a, Test.offsetX, l); // mismatched access; interferes with subsequent load
+        return UNSAFE.getInt(a, Test.offsetY);
+    }
+
+    public static void main(String[] args) {
+        for (int i = 0; i < 20_000; i++) {
+            int res = test(-1L);
+            if (res != -1) {
+                throw new AssertionError("Wrong result: " + res);
+            }
+        }
+        System.out.println("TEST PASSED");
+    }
+}