[turbofan] Allow OptionalOperator to return a placeholder.

src/compiler/wasm-compiler.cc

 // Copyright 2015 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/wasm-compiler.h"
 
 #include "src/isolate-inl.h"
 
 #include "src/base/platform/elapsed-timer.h"
 #include "src/base/platform/platform.h"
@@ skipping 805 matching lines @@
     case wasm::kExprF64ReinterpretI64:
       op = m->BitcastInt64ToFloat64();
       break;
     case wasm::kExprI64ReinterpretF64:
       op = m->BitcastFloat64ToInt64();
       break;
     case wasm::kExprI64Clz:
       op = m->Word64Clz();
       break;
     case wasm::kExprI64Ctz: {
-      if (m->Word64Ctz().IsSupported()) {
-        op = m->Word64Ctz().op();
+      OptionalOperator ctz64 = m->Word64Ctz();
+      if (ctz64.IsSupported()) {
+        op = ctz64.op();
         break;
       } else if (m->Is32() && m->Word32Ctz().IsSupported()) {
-        op = m->Word64CtzPlaceholder();
+        op = ctz64.placeholder();
         break;
       } else if (m->Word64ReverseBits().IsSupported()) {
         Node* reversed = graph()->NewNode(m->Word64ReverseBits().op(), input);
         Node* result = graph()->NewNode(m->Word64Clz(), reversed);
         return result;
       } else {
         return BuildI64Ctz(input);
       }
     }
     case wasm::kExprI64Popcnt: {
-      if (m->Word64Popcnt().IsSupported()) {
-        op = m->Word64Popcnt().op();
+      OptionalOperator popcnt64 = m->Word64Popcnt();
+      if (popcnt64.IsSupported()) {
+        op = popcnt64.op();
       } else if (m->Is32() && m->Word32Popcnt().IsSupported()) {
-        op = m->Word64PopcntPlaceholder();
+        op = popcnt64.placeholder();
       } else {
         return BuildI64Popcnt(input);
       }
       break;
     }
     case wasm::kExprI64Eqz:
       op = m->Word64Equal();
       return graph()->NewNode(op, input, jsgraph()->Int64Constant(0));
     case wasm::kExprF32SConvertI64:
       if (m->Is32()) {
@@ skipping 2607 matching lines @@
                             function_->code_start_offset),
            compile_ms);
   }
 
   return code;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8