[wasm] Added DCHECKs that the input of the Int64Lowering is not null.

src/compiler/int64-lowering.cc

 // Copyright 2014 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/diamond.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/machine-operator.h"
@@ skipping 14 matching lines @@
     : zone_(zone),
       graph_(graph),
       machine_(machine),
       common_(common),
       state_(graph, 3),
       stack_(zone),
       replacements_(nullptr),
       signature_(signature),
       placeholder_(graph->NewNode(common->Parameter(-2, "placeholder"),
                                   graph->start())) {
+  DCHECK_NOT_NULL(graph);
+  DCHECK_NOT_NULL(graph->end());
   replacements_ = zone->NewArray<Replacement>(graph->NodeCount());
   memset(replacements_, 0, sizeof(Replacement) * graph->NodeCount());
 }
 
 void Int64Lowering::LowerGraph() {
   if (!machine()->Is32()) {
     return;
   }
   stack_.push_back({graph()->end(), 0});
   state_.Set(graph()->end(), State::kOnStack);
@@ skipping 753 matching lines @@
                     common()->Phi(MachineRepresentation::kWord32, value_count),
                     value_count + 1, inputs_low, false),
                 graph()->NewNode(
                     common()->Phi(MachineRepresentation::kWord32, value_count),
                     value_count + 1, inputs_high, false));
   }
 }
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8