hotspot/src/share/vm/opto/arraycopynode.cpp
changeset 29337 ef2be52deeaf
child 29340 e5ee51840b93
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/src/share/vm/opto/arraycopynode.cpp	Wed Feb 18 18:14:07 2015 +0100
@@ -0,0 +1,584 @@
+/*
+ * Copyright (c) 2015, 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.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "opto/arraycopynode.hpp"
+#include "opto/graphKit.hpp"
+
+ArrayCopyNode::ArrayCopyNode(Compile* C, bool alloc_tightly_coupled)
+  : CallNode(arraycopy_type(), NULL, TypeRawPtr::BOTTOM),
+    _alloc_tightly_coupled(alloc_tightly_coupled),
+    _kind(None),
+    _arguments_validated(false) {
+  init_class_id(Class_ArrayCopy);
+  init_flags(Flag_is_macro);
+  C->add_macro_node(this);
+}
+
+uint ArrayCopyNode::size_of() const { return sizeof(*this); }
+
+ArrayCopyNode* ArrayCopyNode::make(GraphKit* kit, bool may_throw,
+                                   Node* src, Node* src_offset,
+                                   Node* dest, Node* dest_offset,
+                                   Node* length,
+                                   bool alloc_tightly_coupled,
+                                   Node* src_klass, Node* dest_klass,
+                                   Node* src_length, Node* dest_length) {
+
+  ArrayCopyNode* ac = new ArrayCopyNode(kit->C, alloc_tightly_coupled);
+  Node* prev_mem = kit->set_predefined_input_for_runtime_call(ac);
+
+  ac->init_req(ArrayCopyNode::Src, src);
+  ac->init_req(ArrayCopyNode::SrcPos, src_offset);
+  ac->init_req(ArrayCopyNode::Dest, dest);
+  ac->init_req(ArrayCopyNode::DestPos, dest_offset);
+  ac->init_req(ArrayCopyNode::Length, length);
+  ac->init_req(ArrayCopyNode::SrcLen, src_length);
+  ac->init_req(ArrayCopyNode::DestLen, dest_length);
+  ac->init_req(ArrayCopyNode::SrcKlass, src_klass);
+  ac->init_req(ArrayCopyNode::DestKlass, dest_klass);
+
+  if (may_throw) {
+    ac->set_req(TypeFunc::I_O , kit->i_o());
+    kit->add_safepoint_edges(ac, false);
+  }
+
+  return ac;
+}
+
+void ArrayCopyNode::connect_outputs(GraphKit* kit) {
+  kit->set_all_memory_call(this, true);
+  kit->set_control(kit->gvn().transform(new ProjNode(this,TypeFunc::Control)));
+  kit->set_i_o(kit->gvn().transform(new ProjNode(this, TypeFunc::I_O)));
+  kit->make_slow_call_ex(this, kit->env()->Throwable_klass(), true);
+  kit->set_all_memory_call(this);
+}
+
+#ifndef PRODUCT
+const char* ArrayCopyNode::_kind_names[] = {"arraycopy", "arraycopy, validated arguments", "clone", "oop array clone", "CopyOf", "CopyOfRange"};
+void ArrayCopyNode::dump_spec(outputStream *st) const {
+  CallNode::dump_spec(st);
+  st->print(" (%s%s)", _kind_names[_kind], _alloc_tightly_coupled ? ", tightly coupled allocation" : "");
+}
+#endif
+
+intptr_t ArrayCopyNode::get_length_if_constant(PhaseGVN *phase) const {
+  // check that length is constant
+  Node* length = in(ArrayCopyNode::Length);
+  const Type* length_type = phase->type(length);
+
+  if (length_type == Type::TOP) {
+    return -1;
+  }
+
+  assert(is_clonebasic() || is_arraycopy() || is_copyof() || is_copyofrange(), "unexpected array copy type");
+
+  return is_clonebasic() ? length->find_intptr_t_con(-1) : length->find_int_con(-1);
+}
+
+int ArrayCopyNode::get_count(PhaseGVN *phase) const {
+  Node* src = in(ArrayCopyNode::Src);
+  const Type* src_type = phase->type(src);
+
+  if (is_clonebasic()) {
+    if (src_type->isa_instptr()) {
+      const TypeInstPtr* inst_src = src_type->is_instptr();
+      ciInstanceKlass* ik = inst_src->klass()->as_instance_klass();
+      // ciInstanceKlass::nof_nonstatic_fields() doesn't take injected
+      // fields into account. They are rare anyway so easier to simply
+      // skip instances with injected fields.
+      if ((!inst_src->klass_is_exact() && (ik->is_interface() || ik->has_subklass())) || ik->has_injected_fields()) {
+        return -1;
+      }
+      int nb_fields = ik->nof_nonstatic_fields();
+      return nb_fields;
+    } else {
+      const TypeAryPtr* ary_src = src_type->isa_aryptr();
+      assert (ary_src != NULL, "not an array or instance?");
+      // clone passes a length as a rounded number of longs. If we're
+      // cloning an array we'll do it element by element. If the
+      // length input to ArrayCopyNode is constant, length of input
+      // array must be too.
+
+      assert((get_length_if_constant(phase) == -1) == !ary_src->size()->is_con(), "inconsistent");
+
+      if (ary_src->size()->is_con()) {
+        return ary_src->size()->get_con();
+      }
+      return -1;
+    }
+  }
+
+  return get_length_if_constant(phase);
+}
+
+Node* ArrayCopyNode::try_clone_instance(PhaseGVN *phase, bool can_reshape, int count) {
+  if (!is_clonebasic()) {
+    return NULL;
+  }
+
+  Node* src = in(ArrayCopyNode::Src);
+  Node* dest = in(ArrayCopyNode::Dest);
+  Node* ctl = in(TypeFunc::Control);
+  Node* in_mem = in(TypeFunc::Memory);
+
+  const Type* src_type = phase->type(src);
+  const Type* dest_type = phase->type(dest);
+
+  assert(src->is_AddP(), "should be base + off");
+  assert(dest->is_AddP(), "should be base + off");
+  Node* base_src = src->in(AddPNode::Base);
+  Node* base_dest = dest->in(AddPNode::Base);
+
+  MergeMemNode* mem = MergeMemNode::make(in_mem);
+
+  const TypeInstPtr* inst_src = src_type->isa_instptr();
+
+  if (inst_src == NULL) {
+    return NULL;
+  }
+
+  if (!inst_src->klass_is_exact()) {
+    ciInstanceKlass* ik = inst_src->klass()->as_instance_klass();
+    assert(!ik->is_interface() && !ik->has_subklass(), "inconsistent klass hierarchy");
+    phase->C->dependencies()->assert_leaf_type(ik);
+  }
+
+  ciInstanceKlass* ik = inst_src->klass()->as_instance_klass();
+  assert(ik->nof_nonstatic_fields() <= ArrayCopyLoadStoreMaxElem, "too many fields");
+
+  for (int i = 0; i < count; i++) {
+    ciField* field = ik->nonstatic_field_at(i);
+    int fieldidx = phase->C->alias_type(field)->index();
+    const TypePtr* adr_type = phase->C->alias_type(field)->adr_type();
+    Node* off = phase->MakeConX(field->offset());
+    Node* next_src = phase->transform(new AddPNode(base_src,base_src,off));
+    Node* next_dest = phase->transform(new AddPNode(base_dest,base_dest,off));
+    BasicType bt = field->layout_type();
+
+    const Type *type;
+    if (bt == T_OBJECT) {
+      if (!field->type()->is_loaded()) {
+        type = TypeInstPtr::BOTTOM;
+      } else {
+        ciType* field_klass = field->type();
+        type = TypeOopPtr::make_from_klass(field_klass->as_klass());
+      }
+    } else {
+      type = Type::get_const_basic_type(bt);
+    }
+
+    Node* v = LoadNode::make(*phase, ctl, mem->memory_at(fieldidx), next_src, adr_type, type, bt, MemNode::unordered);
+    v = phase->transform(v);
+    Node* s = StoreNode::make(*phase, ctl, mem->memory_at(fieldidx), next_dest, adr_type, v, bt, MemNode::unordered);
+    s = phase->transform(s);
+    mem->set_memory_at(fieldidx, s);
+  }
+
+  if (!finish_transform(phase, can_reshape, ctl, mem)) {
+    return NULL;
+  }
+
+  return mem;
+}
+
+bool ArrayCopyNode::prepare_array_copy(PhaseGVN *phase, bool can_reshape,
+                                       Node*& adr_src,
+                                       Node*& base_src,
+                                       Node*& adr_dest,
+                                       Node*& base_dest,
+                                       BasicType& copy_type,
+                                       const Type*& value_type,
+                                       bool& disjoint_bases) {
+  Node* src = in(ArrayCopyNode::Src);
+  Node* dest = in(ArrayCopyNode::Dest);
+  const Type* src_type = phase->type(src);
+  const TypeAryPtr* ary_src = src_type->isa_aryptr();
+
+  if (is_arraycopy() || is_copyofrange() || is_copyof()) {
+    const Type* dest_type = phase->type(dest);
+    const TypeAryPtr* ary_dest = dest_type->isa_aryptr();
+    Node* src_offset = in(ArrayCopyNode::SrcPos);
+    Node* dest_offset = in(ArrayCopyNode::DestPos);
+
+    // newly allocated object is guaranteed to not overlap with source object
+    disjoint_bases = is_alloc_tightly_coupled();
+
+    if (ary_src  == NULL || ary_src->klass()  == NULL ||
+        ary_dest == NULL || ary_dest->klass() == NULL) {
+      // We don't know if arguments are arrays
+      return false;
+    }
+
+    BasicType src_elem  = ary_src->klass()->as_array_klass()->element_type()->basic_type();
+    BasicType dest_elem = ary_dest->klass()->as_array_klass()->element_type()->basic_type();
+    if (src_elem  == T_ARRAY)  src_elem  = T_OBJECT;
+    if (dest_elem == T_ARRAY)  dest_elem = T_OBJECT;
+
+    if (src_elem != dest_elem || dest_elem == T_VOID) {
+      // We don't know if arguments are arrays of the same type
+      return false;
+    }
+
+    if (dest_elem == T_OBJECT && (!is_alloc_tightly_coupled() || !GraphKit::use_ReduceInitialCardMarks())) {
+      // It's an object array copy but we can't emit the card marking
+      // that is needed
+      return false;
+    }
+
+    value_type = ary_src->elem();
+
+    base_src = src;
+    base_dest = dest;
+
+    uint shift  = exact_log2(type2aelembytes(dest_elem));
+    uint header = arrayOopDesc::base_offset_in_bytes(dest_elem);
+
+    adr_src = src;
+    adr_dest = dest;
+
+    src_offset = Compile::conv_I2X_index(phase, src_offset, ary_src->size());
+    dest_offset = Compile::conv_I2X_index(phase, dest_offset, ary_dest->size());
+
+    Node* src_scale = phase->transform(new LShiftXNode(src_offset, phase->intcon(shift)));
+    Node* dest_scale = phase->transform(new LShiftXNode(dest_offset, phase->intcon(shift)));
+
+    adr_src = phase->transform(new AddPNode(base_src, adr_src, src_scale));
+    adr_dest = phase->transform(new AddPNode(base_dest, adr_dest, dest_scale));
+
+    adr_src = new AddPNode(base_src, adr_src, phase->MakeConX(header));
+    adr_dest = new AddPNode(base_dest, adr_dest, phase->MakeConX(header));
+
+    adr_src = phase->transform(adr_src);
+    adr_dest = phase->transform(adr_dest);
+
+    copy_type = dest_elem;
+  } else {
+    assert (is_clonebasic(), "should be");
+
+    disjoint_bases = true;
+    assert(src->is_AddP(), "should be base + off");
+    assert(dest->is_AddP(), "should be base + off");
+    adr_src = src;
+    base_src = src->in(AddPNode::Base);
+    adr_dest = dest;
+    base_dest = dest->in(AddPNode::Base);
+
+    assert(phase->type(src->in(AddPNode::Offset))->is_intptr_t()->get_con() == phase->type(dest->in(AddPNode::Offset))->is_intptr_t()->get_con(), "same start offset?");
+    BasicType elem = ary_src->klass()->as_array_klass()->element_type()->basic_type();
+    if (elem == T_ARRAY)  elem = T_OBJECT;
+
+    int diff = arrayOopDesc::base_offset_in_bytes(elem) - phase->type(src->in(AddPNode::Offset))->is_intptr_t()->get_con();
+    assert(diff >= 0, "clone should not start after 1st array element");
+    if (diff > 0) {
+      adr_src = phase->transform(new AddPNode(base_src, adr_src, phase->MakeConX(diff)));
+      adr_dest = phase->transform(new AddPNode(base_dest, adr_dest, phase->MakeConX(diff)));
+    }
+
+    copy_type = elem;
+    value_type = ary_src->elem();
+  }
+  return true;
+}
+
+const TypePtr* ArrayCopyNode::get_address_type(PhaseGVN *phase, Node* n) {
+  const Type* at = phase->type(n);
+  assert(at != Type::TOP, "unexpected type");
+  const TypePtr* atp = at->isa_ptr();
+  // adjust atp to be the correct array element address type
+  atp = atp->add_offset(Type::OffsetBot);
+  return atp;
+}
+
+void ArrayCopyNode::array_copy_test_overlap(PhaseGVN *phase, bool can_reshape, bool disjoint_bases, int count, Node*& forward_ctl, Node*& backward_ctl) {
+  Node* ctl = in(TypeFunc::Control);
+  if (!disjoint_bases && count > 1) {
+    Node* src_offset = in(ArrayCopyNode::SrcPos);
+    Node* dest_offset = in(ArrayCopyNode::DestPos);
+    assert(src_offset != NULL && dest_offset != NULL, "should be");
+    Node* cmp = phase->transform(new CmpINode(src_offset, dest_offset));
+    Node *bol = phase->transform(new BoolNode(cmp, BoolTest::lt));
+    IfNode *iff = new IfNode(ctl, bol, PROB_FAIR, COUNT_UNKNOWN);
+
+    phase->transform(iff);
+
+    forward_ctl = phase->transform(new IfFalseNode(iff));
+    backward_ctl = phase->transform(new IfTrueNode(iff));
+  } else {
+    forward_ctl = ctl;
+  }
+}
+
+Node* ArrayCopyNode::array_copy_forward(PhaseGVN *phase,
+                                        bool can_reshape,
+                                        Node* forward_ctl,
+                                        Node* start_mem_src,
+                                        Node* start_mem_dest,
+                                        const TypePtr* atp_src,
+                                        const TypePtr* atp_dest,
+                                        Node* adr_src,
+                                        Node* base_src,
+                                        Node* adr_dest,
+                                        Node* base_dest,
+                                        BasicType copy_type,
+                                        const Type* value_type,
+                                        int count) {
+  Node* mem = phase->C->top();
+  if (!forward_ctl->is_top()) {
+    // copy forward
+    mem = start_mem_dest;
+
+    if (count > 0) {
+      Node* v = LoadNode::make(*phase, forward_ctl, start_mem_src, adr_src, atp_src, value_type, copy_type, MemNode::unordered);
+      v = phase->transform(v);
+      mem = StoreNode::make(*phase, forward_ctl, mem, adr_dest, atp_dest, v, copy_type, MemNode::unordered);
+      mem = phase->transform(mem);
+      for (int i = 1; i < count; i++) {
+        Node* off  = phase->MakeConX(type2aelembytes(copy_type) * i);
+        Node* next_src = phase->transform(new AddPNode(base_src,adr_src,off));
+        Node* next_dest = phase->transform(new AddPNode(base_dest,adr_dest,off));
+        v = LoadNode::make(*phase, forward_ctl, mem, next_src, atp_src, value_type, copy_type, MemNode::unordered);
+        v = phase->transform(v);
+        mem = StoreNode::make(*phase, forward_ctl,mem,next_dest,atp_dest,v, copy_type, MemNode::unordered);
+        mem = phase->transform(mem);
+      }
+    } else if(can_reshape) {
+      PhaseIterGVN* igvn = phase->is_IterGVN();
+      igvn->_worklist.push(adr_src);
+      igvn->_worklist.push(adr_dest);
+    }
+  }
+  return mem;
+}
+
+Node* ArrayCopyNode::array_copy_backward(PhaseGVN *phase,
+                                         bool can_reshape,
+                                         Node* backward_ctl,
+                                         Node* start_mem_src,
+                                         Node* start_mem_dest,
+                                         const TypePtr* atp_src,
+                                         const TypePtr* atp_dest,
+                                         Node* adr_src,
+                                         Node* base_src,
+                                         Node* adr_dest,
+                                         Node* base_dest,
+                                         BasicType copy_type,
+                                         const Type* value_type,
+                                         int count) {
+  Node* mem = phase->C->top();
+  if (!backward_ctl->is_top()) {
+    // copy backward
+    mem = start_mem_dest;
+
+    if (count > 0) {
+      for (int i = count-1; i >= 1; i--) {
+        Node* off  = phase->MakeConX(type2aelembytes(copy_type) * i);
+        Node* next_src = phase->transform(new AddPNode(base_src,adr_src,off));
+        Node* next_dest = phase->transform(new AddPNode(base_dest,adr_dest,off));
+        Node* v = LoadNode::make(*phase, backward_ctl, mem, next_src, atp_src, value_type, copy_type, MemNode::unordered);
+        v = phase->transform(v);
+        mem = StoreNode::make(*phase, backward_ctl,mem,next_dest,atp_dest,v, copy_type, MemNode::unordered);
+        mem = phase->transform(mem);
+      }
+      Node* v = LoadNode::make(*phase, backward_ctl, mem, adr_src, atp_src, value_type, copy_type, MemNode::unordered);
+      v = phase->transform(v);
+      mem = StoreNode::make(*phase, backward_ctl, mem, adr_dest, atp_dest, v, copy_type, MemNode::unordered);
+      mem = phase->transform(mem);
+    } else if(can_reshape) {
+      PhaseIterGVN* igvn = phase->is_IterGVN();
+      igvn->_worklist.push(adr_src);
+      igvn->_worklist.push(adr_dest);
+    }
+  }
+  return mem;
+}
+
+bool ArrayCopyNode::finish_transform(PhaseGVN *phase, bool can_reshape,
+                                     Node* ctl, Node *mem) {
+  if (can_reshape) {
+    PhaseIterGVN* igvn = phase->is_IterGVN();
+    igvn->set_delay_transform(false);
+    if (is_clonebasic()) {
+      Node* out_mem = proj_out(TypeFunc::Memory);
+
+      if (out_mem->outcnt() != 1 || !out_mem->raw_out(0)->is_MergeMem() ||
+          out_mem->raw_out(0)->outcnt() != 1 || !out_mem->raw_out(0)->raw_out(0)->is_MemBar()) {
+        assert(!GraphKit::use_ReduceInitialCardMarks(), "can only happen with card marking");
+        return false;
+      }
+
+      igvn->replace_node(out_mem->raw_out(0), mem);
+
+      Node* out_ctl = proj_out(TypeFunc::Control);
+      igvn->replace_node(out_ctl, ctl);
+    } else {
+      // replace fallthrough projections of the ArrayCopyNode by the
+      // new memory, control and the input IO.
+      CallProjections callprojs;
+      extract_projections(&callprojs, true);
+
+      igvn->replace_node(callprojs.fallthrough_ioproj, in(TypeFunc::I_O));
+      igvn->replace_node(callprojs.fallthrough_memproj, mem);
+      igvn->replace_node(callprojs.fallthrough_catchproj, ctl);
+
+      // The ArrayCopyNode is not disconnected. It still has the
+      // projections for the exception case. Replace current
+      // ArrayCopyNode with a dummy new one with a top() control so
+      // that this part of the graph stays consistent but is
+      // eventually removed.
+
+      set_req(0, phase->C->top());
+      remove_dead_region(phase, can_reshape);
+    }
+  } else {
+    if (in(TypeFunc::Control) != ctl) {
+      // we can't return new memory and control from Ideal at parse time
+      assert(!is_clonebasic(), "added control for clone?");
+      return NULL;
+    }
+  }
+  return true;
+}
+
+
+Node *ArrayCopyNode::Ideal(PhaseGVN *phase, bool can_reshape) {
+  if (remove_dead_region(phase, can_reshape))  return this;
+
+  if (StressArrayCopyMacroNode && !can_reshape) {
+    phase->record_for_igvn(this);
+    return NULL;
+  }
+
+  // See if it's a small array copy and we can inline it as
+  // loads/stores
+  // Here we can only do:
+  // - arraycopy if all arguments were validated before and we don't
+  // need card marking
+  // - clone for which we don't need to do card marking
+
+  if (!is_clonebasic() && !is_arraycopy_validated() &&
+      !is_copyofrange_validated() && !is_copyof_validated()) {
+    return NULL;
+  }
+
+  if (in(TypeFunc::Control)->is_top() || in(TypeFunc::Memory)->is_top()) {
+    return NULL;
+  }
+
+  int count = get_count(phase);
+
+  if (count < 0 || count > ArrayCopyLoadStoreMaxElem) {
+    return NULL;
+  }
+
+  Node* mem = try_clone_instance(phase, can_reshape, count);
+  if (mem != NULL) {
+    return mem;
+  }
+
+  Node* adr_src = NULL;
+  Node* base_src = NULL;
+  Node* adr_dest = NULL;
+  Node* base_dest = NULL;
+  BasicType copy_type = T_ILLEGAL;
+  const Type* value_type = NULL;
+  bool disjoint_bases = false;
+
+  if (!prepare_array_copy(phase, can_reshape,
+                          adr_src, base_src, adr_dest, base_dest,
+                          copy_type, value_type, disjoint_bases)) {
+    return NULL;
+  }
+
+  Node* src = in(ArrayCopyNode::Src);
+  Node* dest = in(ArrayCopyNode::Dest);
+  const TypePtr* atp_src = get_address_type(phase, src);
+  const TypePtr* atp_dest = get_address_type(phase, dest);
+  uint alias_idx_src = phase->C->get_alias_index(atp_src);
+  uint alias_idx_dest = phase->C->get_alias_index(atp_dest);
+
+  Node *in_mem = in(TypeFunc::Memory);
+  Node *start_mem_src = in_mem;
+  Node *start_mem_dest = in_mem;
+  if (in_mem->is_MergeMem()) {
+    start_mem_src = in_mem->as_MergeMem()->memory_at(alias_idx_src);
+    start_mem_dest = in_mem->as_MergeMem()->memory_at(alias_idx_dest);
+  }
+
+
+  if (can_reshape) {
+    assert(!phase->is_IterGVN()->delay_transform(), "cannot delay transforms");
+    phase->is_IterGVN()->set_delay_transform(true);
+  }
+
+  Node* backward_ctl = phase->C->top();
+  Node* forward_ctl = phase->C->top();
+  array_copy_test_overlap(phase, can_reshape, disjoint_bases, count, forward_ctl, backward_ctl);
+
+  Node* forward_mem = array_copy_forward(phase, can_reshape, forward_ctl,
+                                         start_mem_src, start_mem_dest,
+                                         atp_src, atp_dest,
+                                         adr_src, base_src, adr_dest, base_dest,
+                                         copy_type, value_type, count);
+
+  Node* backward_mem = array_copy_backward(phase, can_reshape, backward_ctl,
+                                           start_mem_src, start_mem_dest,
+                                           atp_src, atp_dest,
+                                           adr_src, base_src, adr_dest, base_dest,
+                                           copy_type, value_type, count);
+
+  Node* ctl = NULL;
+  if (!forward_ctl->is_top() && !backward_ctl->is_top()) {
+    ctl = new RegionNode(3);
+    mem = new PhiNode(ctl, Type::MEMORY, atp_dest);
+    ctl->init_req(1, forward_ctl);
+    mem->init_req(1, forward_mem);
+    ctl->init_req(2, backward_ctl);
+    mem->init_req(2, backward_mem);
+    ctl = phase->transform(ctl);
+    mem = phase->transform(mem);
+  } else if (!forward_ctl->is_top()) {
+    ctl = forward_ctl;
+    mem = forward_mem;
+  } else {
+    assert(!backward_ctl->is_top(), "no copy?");
+    ctl = backward_ctl;
+    mem = backward_mem;
+  }
+
+  if (can_reshape) {
+    assert(phase->is_IterGVN()->delay_transform(), "should be delaying transforms");
+    phase->is_IterGVN()->set_delay_transform(false);
+  }
+
+  MergeMemNode* out_mem = MergeMemNode::make(in_mem);
+  out_mem->set_memory_at(alias_idx_dest, mem);
+  mem = out_mem;
+
+  if (!finish_transform(phase, can_reshape, ctl, mem)) {
+    return NULL;
+  }
+
+  return mem;
+}