[turbofan] Reduce ~~x to x.

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 155 matching lines @@
       }
       break;
     }
     case IrOpcode::kWord32Xor: {
       Int32BinopMatcher m(node);
       if (m.right().Is(0)) return Replace(m.left().node());  // x ^ 0 => x
       if (m.IsFoldable()) {                                  // K ^ K => K
         return ReplaceInt32(m.left().Value() ^ m.right().Value());
       }
       if (m.LeftEqualsRight()) return ReplaceInt32(0);  // x ^ x => 0
+      if (m.left().IsWord32Xor() && m.right().Is(-1)) {
+        Int32BinopMatcher mleft(m.left().node());
+        if (mleft.right().Is(-1)) {  // (x ^ -1) ^ -1 => x
+          return Replace(mleft.left().node());
+        }
+      }
       break;
     }
     case IrOpcode::kWord32Shl: {
       Int32BinopMatcher m(node);
       if (m.right().Is(0)) return Replace(m.left().node());  // x << 0 => x
       if (m.IsFoldable()) {                                  // K << K => K
         return ReplaceInt32(m.left().Value() << m.right().Value());
       }
       if (m.right().IsInRange(1, 31)) {
         // (x >>> K) << K => x & ~(2^K - 1)
@@ skipping 477 matching lines @@
 MachineOperatorBuilder* MachineOperatorReducer::machine() const {
   return jsgraph()->machine();
 }
 
 
 Graph* MachineOperatorReducer::graph() const { return jsgraph()->graph(); }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8