[turbofan] do not emit 2 operations for int64 add with overflow

src/compiler/x64/instruction-selector-x64.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 <algorithm>
 
 #include "src/base/adapters.h"
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
@@ skipping 672 matching lines @@
 
 
 void InstructionSelector::VisitInt64Add(Node* node) {
   VisitBinop(this, node, kX64Add);
 }
 
 
 void InstructionSelector::VisitInt64AddWithOverflow(Node* node) {
   if (Node* ovf = NodeProperties::FindProjection(node, 1)) {
     FlagsContinuation cont = FlagsContinuation::ForSet(kOverflow, ovf);
-    VisitBinop(this, node, kX64Add, &cont);
+    return VisitBinop(this, node, kX64Add, &cont);
   }
   FlagsContinuation cont;
   VisitBinop(this, node, kX64Add, &cont);
 }
 
 
 void InstructionSelector::VisitInt32Sub(Node* node) {
   X64OperandGenerator g(this);
   Int32BinopMatcher m(node);
   if (m.left().Is(0)) {
@@ skipping 1224 matching lines @@
              MachineOperatorBuilder::kFloat64RoundTruncate |
              MachineOperatorBuilder::kFloat32RoundTiesEven |
              MachineOperatorBuilder::kFloat64RoundTiesEven;
   }
   return flags;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8