[wasm] Break effect cycles in the Int64Lowering.

test/unittests/compiler/int64-lowering-unittest.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/int64-lowering.h"
 #include "src/compiler/common-operator.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/machine-operator.h"
 #include "src/compiler/node.h"
 
@@ skipping 831 matching lines @@
 TEST_F(Int64LoweringTest, I64ReverseBytes) {
   LowerGraph(graph()->NewNode(machine()->Word64ReverseBytes().placeholder(),
                               Int64Constant(value(0))),
              MachineRepresentation::kWord64);
   EXPECT_THAT(
       graph()->end()->InputAt(1),
       IsReturn2(IsWord32ReverseBytes(IsInt32Constant(high_word_value(0))),
                 IsWord32ReverseBytes(IsInt32Constant(low_word_value(0))),
                 start(), start()));
 }
+
+TEST_F(Int64LoweringTest, EffectPhiLoop) {
+  // Construct a cycle consisting of an EffectPhi, a Store, and a Load.
+  Node* eff_phi = graph()->NewNode(common()->EffectPhi(1), graph()->start(),
+                                   graph()->start());
+
+  StoreRepresentation store_rep(MachineRepresentation::kWord64,
+                                WriteBarrierKind::kNoWriteBarrier);
+  LoadRepresentation load_rep(MachineType::Int64());
+
+  Node* load =
+      graph()->NewNode(machine()->Load(load_rep), Int64Constant(value(0)),
+                       Int64Constant(value(1)), eff_phi, graph()->start());
+
+  Node* store =
+      graph()->NewNode(machine()->Store(store_rep), Int64Constant(value(0)),
+                       Int64Constant(value(1)), load, load, graph()->start());
+
+  eff_phi->InsertInput(zone(), 1, store);
+  NodeProperties::ChangeOp(eff_phi,
+                           common()->ResizeMergeOrPhi(eff_phi->op(), 2));
+
+  LowerGraph(load, MachineRepresentation::kWord64);
+}
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8