[turbofan] Truncation of Bit/Word8/16 to Word32 is a no-op.

src/compiler/simplified-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/simplified-lowering.h"
 
 #include <limits>
 
 #include "src/base/bits.h"
 #include "src/code-factory.h"
@@ skipping 163 matching lines @@
   }
 
   void ProcessTruncateWord32Input(Node* node, int index, MachineTypeUnion use) {
     Node* input = node->InputAt(index);
     if (phase_ == PROPAGATE) {
       // In the propagate phase, propagate the usage information backward.
       Enqueue(input, use);
     } else {
       // In the change phase, insert a change before the use if necessary.
       MachineTypeUnion output = GetInfo(input)->output;
-      if ((output & kRepWord32) == 0) {
+      if ((output & (kRepBit | kRepWord8 | kRepWord16 | kRepWord32)) == 0) {
         // Output representation doesn't match usage.
         TRACE(("  truncate-to-int32: #%d:%s(@%d #%d:%s) ", node->id(),
                node->op()->mnemonic(), index, input->id(),
                input->op()->mnemonic()));
         TRACE((" from "));
         PrintInfo(output);
         TRACE((" to "));
         PrintInfo(use);
         TRACE(("\n"));
         Node* n = changer_->GetTruncatedWord32For(input, output);
@@ skipping 1282 matching lines @@
 
 void SimplifiedLowering::DoStringLessThanOrEqual(Node* node) {
   node->set_op(machine()->IntLessThanOrEqual());
   node->ReplaceInput(0, StringComparison(node, true));
   node->ReplaceInput(1, jsgraph()->SmiConstant(EQUAL));
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8