8235332: TestInstanceCloneAsLoadsStores.java fails with -XX:+StressGCM

Account for GC barriers when skipping a cloned ArrayCopyNode in ConnectionGraph::find_inst_mem()

Reviewed-by: roland, neliasso

src/hotspot/share/opto/escape.cpp

@@ -2746,11 +2746,14 @@ Node* ConnectionGraph::find_inst_mem(Node *orig_mem, int alias_idx, GrowableArra
           result = proj_in->in(TypeFunc::Memory);
         }
       } else if (proj_in->is_MemBar()) {
-        if (proj_in->in(TypeFunc::Memory)->is_MergeMem() &&
-            proj_in->in(TypeFunc::Memory)->as_MergeMem()->in(Compile::AliasIdxRaw)->is_Proj() &&
-            proj_in->in(TypeFunc::Memory)->as_MergeMem()->in(Compile::AliasIdxRaw)->in(0)->is_ArrayCopy()) {
-          // clone
-          ArrayCopyNode* ac = proj_in->in(TypeFunc::Memory)->as_MergeMem()->in(Compile::AliasIdxRaw)->in(0)->as_ArrayCopy();
+        // Check if there is an array copy for a clone
+        // Step over GC barrier when ReduceInitialCardMarks is disabled
+        BarrierSetC2* bs = BarrierSet::barrier_set()->barrier_set_c2();
+        Node* control_proj_ac = bs->step_over_gc_barrier(proj_in->in(0));
+
+        if (control_proj_ac->is_Proj() && control_proj_ac->in(0)->is_ArrayCopy()) {
+          // Stop if it is a clone
+          ArrayCopyNode* ac = control_proj_ac->in(0)->as_ArrayCopy();
           if (ac->may_modify(toop, igvn)) {
             break;
           }

test/hotspot/jtreg/compiler/arraycopy/TestCloneAccessStressGCM.java

@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2020, 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 8235332
+ * @summary Test cloning with more than 8 (=ArrayCopyLoadStoreMaxElem) fields with StressGCM
+ * @library /
+ *
+ * @run main/othervm -Xbatch
+ *                   -XX:CompileCommand=dontinline,compiler.arraycopy.TestCloneAccessStressGCM::test
+ *                   -XX:+UnlockDiagnosticVMOptions -XX:+StressGCM -XX:-ReduceInitialCardMarks
+ *                   compiler.arraycopy.TestCloneAccessStressGCM
+ */
+
+package compiler.arraycopy;
+
+public class TestCloneAccessStressGCM {
+
+    static int test(E src) throws CloneNotSupportedException {
+        // ArrayCopyNode for this clone is not inlined since there are more than 8 (=ArrayCopyLoadStoreMaxElem) fields
+        E dest = (E)src.clone();
+
+        // The ArrayCopyNode initialization for the clone is executed after the LoadI nodes for 'dest' due to a
+        // memory input from the uninitialized new object instead of the ArrayCopyNode. As a result, uninitialized
+        // memory is read for each field and added together.
+        return dest.i1 + dest.i2 + dest.i3 + dest.i4 + dest.i5 +
+            dest.i6 + dest.i7 + dest.i8 + dest.i9;
+    }
+
+    public static void main(String[] args) throws Exception {
+        TestCloneAccessStressGCM test = new TestCloneAccessStressGCM();
+        int result = 0;
+        E e = new E();
+        for (int i = 0; i < 20000; i++) {
+            result = test(e);
+            if (result != 36) {
+              throw new RuntimeException("Return value not 36. Got: " + result + "; additional check:  " + e.sum());
+            }
+        }
+
+        if (result != 36) {
+            throw new RuntimeException("Return value not 36. Got: " + result + "; additional check:  " + e.sum());
+        }
+    }
+}
+
+class E implements Cloneable {
+    /*
+     * Need more than 8 (=ArrayCopyLoadStoreMaxElem) fields
+     */
+    int i1;
+    int i2;
+    int i3;
+    int i4;
+    int i5;
+    int i6;
+    int i7;
+    int i8;
+    int i9;
+
+    E() {
+        i1 = 0;
+        i2 = 1;
+        i3 = 2;
+        i4 = 3;
+        i5 = 4;
+        i6 = 5;
+        i7 = 6;
+        i8 = 7;
+        i9 = 8;
+    }
+
+    public Object clone() throws CloneNotSupportedException {
+        return super.clone();
+    }
+
+    public int sum() {
+        return i1 + i2 + i3 + i4 + i5 + i6 + i7 + i8 + i9;
+    }
+}
+