[turbofan] Drop the obsolete TypeGuard operator.

src/compiler/load-elimination.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/load-elimination.h"
 
 #include "src/compiler/graph.h"
 #include "src/compiler/node-properties.h"
 #include "src/compiler/simplified-operator.h"
 #include "src/types.h"
@@ skipping 43 matching lines @@
           return Replace(value);
         }
         break;
       }
       case IrOpcode::kStoreField: {
         if (access == FieldAccessOf(effect->op())) {
           Node* value_input = NormalizeCheckTaggedPointer(
               NodeProperties::GetValueInput(effect, 0));
           if (object == value_input) {
             Node* const value = NodeProperties::GetValueInput(effect, 1);
-            Type* stored_value_type = NodeProperties::GetType(value);
-            Type* load_type = NodeProperties::GetType(node);
+            Type* value_type = NodeProperties::GetType(value);
+            Type* node_type = NodeProperties::GetType(node);
             // Make sure the replacement's type is a subtype of the node's
             // type. Otherwise we could confuse optimizations that were
             // based on the original type.
-            if (stored_value_type->Is(load_type)) {
+            if (value_type->Is(node_type)) {
               ReplaceWithValue(node, value);
               return Replace(value);
             } else {
-              Node* renamed = graph()->NewNode(
-                  simplified()->TypeGuard(Type::Intersect(
-                      stored_value_type, load_type, graph()->zone())),
-                  value, NodeProperties::GetControlInput(node));
-              ReplaceWithValue(node, renamed);
-              return Replace(renamed);
+              // This LoadField has stronger guarantees than the stored value
+              // can give us, which suggests that we are probably in unreachable
+              // code, guarded by some Check, so don't bother trying to optimize
+              // this LoadField {node}.
+              return NoChange();
             }
           }
           // TODO(turbofan): Alias analysis to the rescue?
           return NoChange();
         }
         break;
       }
       case IrOpcode::kBeginRegion:
       case IrOpcode::kStoreBuffer:
       case IrOpcode::kStoreElement: {
@@ skipping 22 matching lines @@
       }
     }
   }
   UNREACHABLE();
   return NoChange();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8