MIPS:[turbofan] Use Nor instruction for bit negation instead of xori.

src/compiler/mips64/instruction-selector-mips64.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/base/adapters.h"
 #include "src/base/bits.h"
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 
@@ skipping 341 matching lines @@
       m.right().Is(-1)) {
     Int32BinopMatcher mleft(m.left().node());
     if (!mleft.right().HasValue()) {
       Mips64OperandGenerator g(this);
       Emit(kMips64Nor, g.DefineAsRegister(node),
            g.UseRegister(mleft.left().node()),
            g.UseRegister(mleft.right().node()));
       return;
     }
   }
+  if (m.right().Is(-1)) {
+    // Use Nor for bit negation and eliminate constant loading for xori.
+    Mips64OperandGenerator g(this);
+    Emit(kMips64Nor, g.DefineAsRegister(node), g.UseRegister(m.left().node()),
+         g.TempImmediate(0));
+    return;
+  }
   VisitBinop(this, node, kMips64Xor);
 }
 
 
 void InstructionSelector::VisitWord64Xor(Node* node) {
   Int64BinopMatcher m(node);
   if (m.left().IsWord64Or() && CanCover(node, m.left().node()) &&
       m.right().Is(-1)) {
     Int64BinopMatcher mleft(m.left().node());
     if (!mleft.right().HasValue()) {
       Mips64OperandGenerator g(this);
       Emit(kMips64Nor, g.DefineAsRegister(node),
            g.UseRegister(mleft.left().node()),
            g.UseRegister(mleft.right().node()));
       return;
     }
   }
+  if (m.right().Is(-1)) {
+    // Use Nor for bit negation and eliminate constant loading for xori.
+    Mips64OperandGenerator g(this);
+    Emit(kMips64Nor, g.DefineAsRegister(node), g.UseRegister(m.left().node()),
+         g.TempImmediate(0));
+    return;
+  }
   VisitBinop(this, node, kMips64Xor);
 }
 
 
 void InstructionSelector::VisitWord32Shl(Node* node) {
   VisitRRO(this, kMips64Shl, node);
 }
 
 
 void InstructionSelector::VisitWord32Shr(Node* node) {
@@ skipping 1232 matching lines @@
          MachineOperatorBuilder::kFloat32RoundUp |
          MachineOperatorBuilder::kFloat64RoundTruncate |
          MachineOperatorBuilder::kFloat32RoundTruncate |
          MachineOperatorBuilder::kFloat64RoundTiesEven |
          MachineOperatorBuilder::kFloat32RoundTiesEven;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8