[turbofan] Don't call String::Flatten in Constant::ToHeapObject()

src/compiler/instruction.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/common-operator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/instruction.h"
 #include "src/compiler/schedule.h"
 #include "src/compiler/state-values-utils.h"
 
@@ skipping 501 matching lines @@
     UNREACHABLE();
   }
   value_ = info.value();
   rmode_ = info.rmode();
 }
 
 Handle<HeapObject> Constant::ToHeapObject() const {
   DCHECK_EQ(kHeapObject, type());
   Handle<HeapObject> value(
       bit_cast<HeapObject**>(static_cast<intptr_t>(value_)));
-  if (value->IsConsString()) {
-    value = String::Flatten(Handle<String>::cast(value), TENURED);
-  }
   return value;
 }
 
 std::ostream& operator<<(std::ostream& os, const Constant& constant) {
   switch (constant.type()) {
     case Constant::kInt32:
       return os << constant.ToInt32();
     case Constant::kInt64:
       return os << constant.ToInt64() << "l";
     case Constant::kFloat32:
@@ skipping 483 matching lines @@
   }
   for (int i = 0; i < code.InstructionBlockCount(); i++) {
     printable.sequence_->PrintBlock(printable.register_configuration_, i);
   }
   return os;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8