--- a/src/share/vm/opto/arraycopynode.cpp	Thu Jun 22 18:42:45 2017 +0000
+++ b/src/share/vm/opto/arraycopynode.cpp	Fri Jun 23 09:33:21 2017 +0200
@@ -748,41 +748,3 @@
   return false;
 }
 
-// We try to replace a load from the destination of an arraycopy with
-// a load from the source so the arraycopy has a chance to be
-// eliminated. It's only valid if the arraycopy doesn't change the
-// element that would be loaded from the source array.
-bool ArrayCopyNode::can_replace_dest_load_with_src_load(intptr_t offset_lo, intptr_t offset_hi, PhaseTransform* phase) const {
-  assert(_kind == ArrayCopy || _kind == CopyOf || _kind == CopyOfRange, "only for real array copies");
-
-  Node* src = in(Src);
-  Node* dest = in(Dest);
-
-  // Check whether, assuming source and destination are the same
-  // array, the arraycopy modifies the element from the source we
-  // would load.
-  if ((src != dest && in(SrcPos) == in(DestPos)) || !modifies(offset_lo, offset_hi, phase, false)) {
-    // if not the transformation is legal
-    return true;
-  }
-
-  AllocateNode* src_alloc = AllocateNode::Ideal_allocation(src, phase);
-  AllocateNode* dest_alloc = AllocateNode::Ideal_allocation(dest, phase);
-
-  // Check whether source and destination can be proved to be
-  // different arrays
-  const TypeOopPtr* t_src = phase->type(src)->isa_oopptr();
-  const TypeOopPtr* t_dest = phase->type(dest)->isa_oopptr();
-
-  if (t_src != NULL && t_dest != NULL &&
-      (t_src->is_known_instance() || t_dest->is_known_instance()) &&
-      t_src->instance_id() != t_dest->instance_id()) {
-    return true;
-  }
-
-  if (MemNode::detect_ptr_independence(src->uncast(), src_alloc, dest->uncast(), dest_alloc, phase)) {
-    return true;
-  }
-
-  return false;
-}

--- a/src/share/vm/opto/arraycopynode.hpp	Thu Jun 22 18:42:45 2017 +0000
+++ b/src/share/vm/opto/arraycopynode.hpp	Fri Jun 23 09:33:21 2017 +0200
@@ -168,7 +168,6 @@
 
   static bool may_modify(const TypeOopPtr *t_oop, MemBarNode* mb, PhaseTransform *phase, ArrayCopyNode*& ac);
   bool modifies(intptr_t offset_lo, intptr_t offset_hi, PhaseTransform* phase, bool must_modify) const;
-  bool can_replace_dest_load_with_src_load(intptr_t offset_lo, intptr_t offset_hi, PhaseTransform* phase) const;
 
 #ifndef PRODUCT
   virtual void dump_spec(outputStream *st) const;

--- a/src/share/vm/opto/library_call.cpp	Thu Jun 22 18:42:45 2017 +0000
+++ b/src/share/vm/opto/library_call.cpp	Fri Jun 23 09:33:21 2017 +0200
@@ -5171,6 +5171,10 @@
                     Deoptimization::Action_make_not_entrant);
       assert(stopped(), "Should be stopped");
     }
+
+    const TypeKlassPtr* dest_klass_t = _gvn.type(dest_klass)->is_klassptr();
+    const Type *toop = TypeOopPtr::make_from_klass(dest_klass_t->klass());
+    src = _gvn.transform(new CheckCastPPNode(control(), src, toop));
   }
 
   arraycopy_move_allocation_here(alloc, dest, saved_jvms, saved_reexecute_sp, new_idx);

--- a/src/share/vm/opto/memnode.cpp	Thu Jun 22 18:42:45 2017 +0000
+++ b/src/share/vm/opto/memnode.cpp	Fri Jun 23 09:33:21 2017 +0200
@@ -885,7 +885,7 @@
 // Is the value loaded previously stored by an arraycopy? If so return
 // a load node that reads from the source array so we may be able to
 // optimize out the ArrayCopy node later.
-Node* LoadNode::can_see_arraycopy_value(Node* st, PhaseTransform* phase) const {
+Node* LoadNode::can_see_arraycopy_value(Node* st, PhaseGVN* phase) const {
   Node* ld_adr = in(MemNode::Address);
   intptr_t ld_off = 0;
   AllocateNode* ld_alloc = AllocateNode::Ideal_allocation(ld_adr, phase, ld_off);
@@ -893,23 +893,27 @@
   if (ac != NULL) {
     assert(ac->is_ArrayCopy(), "what kind of node can this be?");
 
-    Node* ld = clone();
+    Node* mem = ac->in(TypeFunc::Memory);
+    Node* ctl = ac->in(0);
+    Node* src = ac->in(ArrayCopyNode::Src);
+
+    if (!ac->as_ArrayCopy()->is_clonebasic() && !phase->type(src)->isa_aryptr()) {
+      return NULL;
+    }
+
+    LoadNode* ld = clone()->as_Load();
+    Node* addp = in(MemNode::Address)->clone();
     if (ac->as_ArrayCopy()->is_clonebasic()) {
       assert(ld_alloc != NULL, "need an alloc");
-      Node* addp = in(MemNode::Address)->clone();
       assert(addp->is_AddP(), "address must be addp");
       assert(addp->in(AddPNode::Base) == ac->in(ArrayCopyNode::Dest)->in(AddPNode::Base), "strange pattern");
       assert(addp->in(AddPNode::Address) == ac->in(ArrayCopyNode::Dest)->in(AddPNode::Address), "strange pattern");
-      addp->set_req(AddPNode::Base, ac->in(ArrayCopyNode::Src)->in(AddPNode::Base));
-      addp->set_req(AddPNode::Address, ac->in(ArrayCopyNode::Src)->in(AddPNode::Address));
-      ld->set_req(MemNode::Address, phase->transform(addp));
-      if (in(0) != NULL) {
-        assert(ld_alloc->in(0) != NULL, "alloc must have control");
-        ld->set_req(0, ld_alloc->in(0));
-      }
+      addp->set_req(AddPNode::Base, src->in(AddPNode::Base));
+      addp->set_req(AddPNode::Address, src->in(AddPNode::Address));
     } else {
-      Node* src = ac->in(ArrayCopyNode::Src);
-      Node* addp = in(MemNode::Address)->clone();
+      assert(ac->as_ArrayCopy()->is_arraycopy_validated() ||
+             ac->as_ArrayCopy()->is_copyof_validated() ||
+             ac->as_ArrayCopy()->is_copyofrange_validated(), "only supported cases");
       assert(addp->in(AddPNode::Base) == addp->in(AddPNode::Address), "should be");
       addp->set_req(AddPNode::Base, src);
       addp->set_req(AddPNode::Address, src);
@@ -927,21 +931,17 @@
 
       Node* offset = phase->transform(new AddXNode(addp->in(AddPNode::Offset), diff));
       addp->set_req(AddPNode::Offset, offset);
-      ld->set_req(MemNode::Address, phase->transform(addp));
-
-      const TypeX *ld_offs_t = phase->type(offset)->isa_intptr_t();
-
-      if (!ac->as_ArrayCopy()->can_replace_dest_load_with_src_load(ld_offs_t->_lo, ld_offs_t->_hi, phase)) {
-        return NULL;
-      }
-
-      if (in(0) != NULL) {
-        assert(ac->in(0) != NULL, "alloc must have control");
-        ld->set_req(0, ac->in(0));
-      }
     }
+    addp = phase->transform(addp);
+#ifdef ASSERT
+    const TypePtr* adr_type = phase->type(addp)->is_ptr();
+    ld->_adr_type = adr_type;
+#endif
+    ld->set_req(MemNode::Address, addp);
+    ld->set_req(0, ctl);
+    ld->set_req(MemNode::Memory, mem);
     // load depends on the tests that validate the arraycopy
-    ld->as_Load()->_control_dependency = Pinned;
+    ld->_control_dependency = Pinned;
     return ld;
   }
   return NULL;

--- a/src/share/vm/opto/memnode.hpp	Thu Jun 22 18:42:45 2017 +0000
+++ b/src/share/vm/opto/memnode.hpp	Fri Jun 23 09:33:21 2017 +0200
@@ -270,7 +270,7 @@
   const Type* load_array_final_field(const TypeKlassPtr *tkls,
                                      ciKlass* klass) const;
 
-  Node* can_see_arraycopy_value(Node* st, PhaseTransform* phase) const;
+  Node* can_see_arraycopy_value(Node* st, PhaseGVN* phase) const;
 
   // depends_only_on_test is almost always true, and needs to be almost always
   // true to enable key hoisting & commoning optimizations.  However, for the

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/compiler/arraycopy/TestLoadBypassACWithWrongMem.java	Fri Jun 23 09:33:21 2017 +0200
@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 2017, Red Hat, Inc. 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 8181742
+ * @summary Loads that bypass arraycopy ends up with wrong memory state
+ *
+ * @run main/othervm -XX:-BackgroundCompilation -XX:-UseOnStackReplacement -XX:+UnlockDiagnosticVMOptions -XX:+IgnoreUnrecognizedVMOptions -XX:+StressGCM -XX:+StressLCM TestLoadBypassACWithWrongMem
+ *
+ */
+
+import java.util.Arrays;
+
+public class TestLoadBypassACWithWrongMem {
+
+    static int test1(int[] src) {
+        int[] dst = new int[10];
+        System.arraycopy(src, 0, dst, 0, 10);
+        src[1] = 0x42;
+        // dst[1] is transformed to src[1], src[1] must use the
+        // correct memory state (not the store above).
+        return dst[1];
+    }
+
+    static int test2(int[] src) {
+        int[] dst = (int[])src.clone();
+        src[1] = 0x42;
+        // Same as above for clone
+        return dst[1];
+    }
+
+    static Object test5_src = null;
+    static int test3() {
+        int[] dst = new int[10];
+        System.arraycopy(test5_src, 0, dst, 0, 10);
+        ((int[])test5_src)[1] = 0x42;
+        System.arraycopy(test5_src, 0, dst, 0, 10);
+        // dst[1] is transformed to test5_src[1]. test5_src is Object
+        // but test5_src[1] must be on the slice for int[] not
+        // Object+some offset.
+        return dst[1];
+    }
+
+    static public void main(String[] args) {
+        int[] src = new int[10];
+        for (int i = 0; i < 20000; i++) {
+            Arrays.fill(src, 0);
+            int res = test1(src);
+            if (res != 0) {
+                throw new RuntimeException("bad result: " + res + " != " + 0);
+            }
+            Arrays.fill(src, 0);
+            res = test2(src);
+            if (res != 0) {
+                throw new RuntimeException("bad result: " + res + " != " + 0);
+            }
+            Arrays.fill(src, 0);
+            test5_src = src;
+            res = test3();
+            if (res != 0x42) {
+                throw new RuntimeException("bad result: " + res + " != " + 0x42);
+            }
+         }
+    }
+}