CTZ instruction implemented as optional operator.

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 560 matching lines @@
   VisitWord64Shift(this, node, kX64Ror);
 }
 
 
 void InstructionSelector::VisitWord32Clz(Node* node) {
   X64OperandGenerator g(this);
   Emit(kX64Lzcnt32, g.DefineAsRegister(node), g.Use(node->InputAt(0)));
 }
 
 
+void InstructionSelector::VisitWord32Ctz(Node* node) { UNREACHABLE(); }

[titzer, 2015/10/12 23:48:48]

Can we go ahead and implement this on at least one architecture?

+
+
 void InstructionSelector::VisitInt32Add(Node* node) {
   X64OperandGenerator g(this);
 
   // Try to match the Add to a leal pattern
   BaseWithIndexAndDisplacement32Matcher m(node);
   if (m.matches() &&
       (m.displacement() == NULL || g.CanBeImmediate(m.displacement()))) {
     EmitLea(this, kX64Lea32, node, m.index(), m.scale(), m.base(),
             m.displacement());
     return;
@@ skipping 1117 matching lines @@
   if (CpuFeatures::IsSupported(SSE4_1)) {
     flags |= MachineOperatorBuilder::kFloat64RoundDown |
              MachineOperatorBuilder::kFloat64RoundTruncate;
   }
   return flags;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8