8240795: [REDO] 8238384 CTW: C2 compilation fails with "assert(store != load->find_exact_control(load->in(0))) failed: dependence cycle found"

Reviewed-by: kvn, thartmann

src/hotspot/share/opto/compile.cpp

@@ -1700,8 +1700,9 @@ bool Compile::must_alias(const TypePtr* adr_type, int alias_idx) {
 bool Compile::can_alias(const TypePtr* adr_type, int alias_idx) {
   if (alias_idx == AliasIdxTop)         return false; // the empty category
   if (adr_type == NULL)                 return false; // NULL serves as TypePtr::TOP
-  if (alias_idx == AliasIdxBot)         return true;  // the universal category
-  if (adr_type->base() == Type::AnyPtr) return true;  // TypePtr::BOTTOM or its twins
+  // Known instance doesn't alias with bottom memory
+  if (alias_idx == AliasIdxBot)         return !adr_type->is_known_instance();                   // the universal category
+  if (adr_type->base() == Type::AnyPtr) return !C->get_adr_type(alias_idx)->is_known_instance(); // TypePtr::BOTTOM or its twins
 
   // the only remaining possible overlap is identity
   int adr_idx = get_alias_index(adr_type);

src/hotspot/share/opto/gcm.cpp

@@ -707,19 +707,6 @@ Block* PhaseCFG::insert_anti_dependences(Block* LCA, Node* load, bool verify) {
         // instead of control + memory.
         if (mstore->ideal_Opcode() == Op_SafePoint)
           continue;
-
-        // Check if the store is a membar on which the load is control dependent.
-        // Inserting an anti-dependency between that membar and the load would
-        // create a cycle that causes local scheduling to fail.
-        if (mstore->isa_MachMemBar()) {
-          Node* dom = load->find_exact_control(load->in(0));
-          while (dom != NULL && dom != dom->in(0) && dom != mstore) {
-            dom = dom->in(0);
-          }
-          if (dom == mstore) {
-            continue;
-          }
-        }
       } else {
         // Some raw memory, such as the load of "top" at an allocation,
         // can be control dependent on the previous safepoint. See

src/hotspot/share/opto/loopnode.cpp

@@ -31,6 +31,7 @@
 #include "memory/allocation.inline.hpp"
 #include "memory/resourceArea.hpp"
 #include "opto/addnode.hpp"
+#include "opto/arraycopynode.hpp"
 #include "opto/callnode.hpp"
 #include "opto/connode.hpp"
 #include "opto/convertnode.hpp"
@@ -4089,8 +4090,16 @@ Node *PhaseIdealLoop::get_late_ctrl( Node *n, Node *early ) {
           }
         } else {
           Node *sctrl = has_ctrl(s) ? get_ctrl(s) : s->in(0);
+          const TypePtr* adr_type = s->adr_type();
+          if (s->is_ArrayCopy()) {
+            // Copy to known instance needs destination type to test for aliasing
+            const TypePtr* dest_type = s->as_ArrayCopy()->_dest_type;
+            if (dest_type != TypeOopPtr::BOTTOM) {
+              adr_type = dest_type;
+            }
+          }
           assert(sctrl != NULL || !s->is_reachable_from_root(), "must have control");
-          if (sctrl != NULL && !sctrl->is_top() && C->can_alias(s->adr_type(), load_alias_idx) && is_dominator(early, sctrl)) {
+          if (sctrl != NULL && !sctrl->is_top() && C->can_alias(adr_type, load_alias_idx) && is_dominator(early, sctrl)) {
             LCA = dom_lca_for_get_late_ctrl(LCA, sctrl, n);
           }
         }

src/hotspot/share/opto/type.hpp

@@ -452,6 +452,7 @@ public:
   const Type* maybe_remove_speculative(bool include_speculative) const;
 
   virtual bool maybe_null() const { return true; }
+  virtual bool is_known_instance() const { return false; }
 
 private:
   // support arrays
@@ -1397,6 +1398,10 @@ public:
     return _ptrtype;
   }
 
+  bool is_known_instance() const {
+    return _ptrtype->is_known_instance();
+  }
+
 #ifndef PRODUCT
   virtual void dump2( Dict &d, uint depth, outputStream *st ) const;
 #endif

test/hotspot/jtreg/compiler/escapeAnalysis/TestCopyOfBrokenAntiDependency.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2020, 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 8238384
+ * @summary CTW: C2 compilation fails with "assert(store != load->find_exact_control(load->in(0))) failed: dependence cycle found"
+ *
+ * @run main/othervm -XX:-BackgroundCompilation TestCopyOfBrokenAntiDependency
+ *
+ */
+
+import java.util.Arrays;
+
+public class TestCopyOfBrokenAntiDependency {
+
+    public static void main(String[] args) {
+        for (int i = 0; i < 20_000; i++) {
+            test(100);
+        }
+    }
+
+    private static Object test(int length) {
+        Object[] src  = new Object[length]; // non escaping
+        final Object[] dst = Arrays.copyOf(src, 10); // can't be removed
+        final Object[] dst2 = Arrays.copyOf(dst, 100);
+        // load is control dependent on membar from previous copyOf
+        // but has memory edge to first copyOf.
+        final Object v = dst[0];
+        return v;
+    }
+}