[turbofan] Introduce a dedicated ConvertTaggedHoleToUndefined operator.

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/address-map.h"
 #include "src/base/bits.h"
@@ skipping 2374 matching lines @@
         ProcessInput(node, 0, UseInfo::TruncatingFloat64());
         ProcessRemainingInputs(node, 1);
         SetOutput(node, MachineRepresentation::kFloat64);
         if (truncation.IsUsedAsFloat64() &&
             mode == CheckFloat64HoleMode::kAllowReturnHole) {
           if (lower()) DeferReplacement(node, node->InputAt(0));
         }
         return;
       }
       case IrOpcode::kCheckTaggedHole: {
-        CheckTaggedHoleMode mode = CheckTaggedHoleModeOf(node->op());
-        if (truncation.IsUsedAsWord32() &&
-            mode == CheckTaggedHoleMode::kConvertHoleToUndefined) {
-          ProcessInput(node, 0, UseInfo::CheckedSigned32AsWord32());
-          ProcessRemainingInputs(node, 1);
-          SetOutput(node, MachineRepresentation::kWord32);
+        VisitUnop(node, UseInfo::AnyTagged(), MachineRepresentation::kTagged);
+        return;
+      }
+      case IrOpcode::kConvertTaggedHoleToUndefined: {
+        if (InputIs(node, Type::NumberOrOddball()) &&
+            truncation.IsUsedAsWord32()) {
+          // Propagate the Word32 truncation.
+          VisitUnop(node, UseInfo::TruncatingWord32(),
+                    MachineRepresentation::kWord32);
+          if (lower()) DeferReplacement(node, node->InputAt(0));
+        } else if (InputIs(node, Type::NumberOrOddball()) &&
+                   truncation.IsUsedAsFloat64()) {
+          // Propagate the Float64 truncation.
+          VisitUnop(node, UseInfo::TruncatingFloat64(),
+                    MachineRepresentation::kFloat64);
+          if (lower()) DeferReplacement(node, node->InputAt(0));
+        } else if (InputIs(node, Type::NonInternal())) {
+          VisitUnop(node, UseInfo::AnyTagged(), MachineRepresentation::kTagged);
           if (lower()) DeferReplacement(node, node->InputAt(0));
         } else {
-          ProcessInput(node, 0, UseInfo::AnyTagged());
-          ProcessRemainingInputs(node, 1);
-          SetOutput(node, MachineRepresentation::kTagged);
+          // TODO(turbofan): Add a (Tagged) truncation that identifies hole
+          // and undefined, i.e. for a[i] === obj cases.
+          VisitUnop(node, UseInfo::AnyTagged(), MachineRepresentation::kTagged);
         }
         return;
       }
       case IrOpcode::kCheckMaps:
       case IrOpcode::kTransitionElementsKind: {
         VisitInputs(node);
         return SetOutput(node, MachineRepresentation::kNone);
       }
       case IrOpcode::kEnsureWritableFastElements:
         return VisitBinop(node, UseInfo::AnyTagged(),
@@ skipping 928 matching lines @@
         isolate(), graph()->zone(), callable.descriptor(), 0, flags,
         Operator::kNoProperties);
     to_number_operator_.set(common()->Call(desc));
   }
   return to_number_operator_.get();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8