[turbofan] Improve code generation for inline comparisons with zero.

src/compiler/machine-operator-reducer.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/machine-operator-reducer.h"
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
 #include "src/codegen.h"
 #include "src/compiler/generic-node-inl.h"
@@ skipping 225 matching lines @@
       if (m.left().IsInt32Sub() && m.right().Is(0)) {  // x - y == 0 => x == y
         Int32BinopMatcher msub(m.left().node());
         node->ReplaceInput(0, msub.left().node());
         node->ReplaceInput(1, msub.right().node());
         return Changed(node);
       }
       // TODO(turbofan): fold HeapConstant, ExternalReference, pointer compares
       if (m.LeftEqualsRight()) return ReplaceBool(true);  // x == x => true
       break;
     }
+    case IrOpcode::kWord64Equal: {
+      Int64BinopMatcher m(node);
+      if (m.IsFoldable()) {  // K == K => K
+        return ReplaceBool(m.left().Value() == m.right().Value());
+      }
+      if (m.left().IsInt64Sub() && m.right().Is(0)) {  // x - y == 0 => x == y
+        Int64BinopMatcher msub(m.left().node());
+        node->ReplaceInput(0, msub.left().node());
+        node->ReplaceInput(1, msub.right().node());
+        return Changed(node);
+      }
+      // TODO(turbofan): fold HeapConstant, ExternalReference, pointer compares
+      if (m.LeftEqualsRight()) return ReplaceBool(true);  // x == x => true
+      break;
+    }
     case IrOpcode::kInt32Add: {
       Int32BinopMatcher m(node);
       if (m.right().Is(0)) return Replace(m.left().node());  // x + 0 => x
       if (m.IsFoldable()) {                                  // K + K => K
         return ReplaceInt32(static_cast<uint32_t>(m.left().Value()) +
                             static_cast<uint32_t>(m.right().Value()));
       }
       break;
     }
     case IrOpcode::kInt32Sub: {
@@ skipping 413 matching lines @@
 MachineOperatorBuilder* MachineOperatorReducer::machine() const {
   return jsgraph()->machine();
 }
 
 
 Graph* MachineOperatorReducer::graph() const { return jsgraph()->graph(); }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8