[vm] Remove Dart_MakeExternalString and --support-externalizable-strings

runtime/vm/constant_propagator.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #if !defined(DART_PRECOMPILED_RUNTIME)
 
 #include "vm/constant_propagator.h"
 
 #include "vm/bit_vector.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 271 matching lines @@
     }
   }
   if (!SetValue(instr, value) &&
       marked_phis_->Contains(instr->ssa_temp_index())) {
     marked_phis_->Remove(instr->ssa_temp_index());
     definition_worklist_.Add(instr);
   }
 }
 
 void ConstantPropagator::VisitRedefinition(RedefinitionInstr* instr) {
-  // Ensure that we never remove redefinition of a constant unless we are also
-  // are guaranteed to fold away code paths that correspond to non-matching
-  // class ids. Otherwise LICM might potentially hoist incorrect code.
   const Object& value = instr->value()->definition()->constant_value();
-  if (IsConstant(value) && !Field::IsExternalizableCid(value.GetClassId())) {
+  if (IsConstant(value)) {
     SetValue(instr, value);
   } else {
     SetValue(instr, non_constant_);
   }
 }
 
 void ConstantPropagator::VisitParameter(ParameterInstr* instr) {
   SetValue(instr, non_constant_);
 }
 
@@ skipping 422 matching lines @@
 void ConstantPropagator::VisitLoadClassId(LoadClassIdInstr* instr) {
   intptr_t cid = instr->object()->Type()->ToCid();
   if (cid != kDynamicCid) {
     SetValue(instr, Smi::ZoneHandle(Z, Smi::New(cid)));
     return;
   }
 
   const Object& object = instr->object()->definition()->constant_value();
   if (IsConstant(object)) {
     cid = object.GetClassId();
-    if (!Field::IsExternalizableCid(cid)) {
-      SetValue(instr, Smi::ZoneHandle(Z, Smi::New(cid)));
-      return;
-    }
+    SetValue(instr, Smi::ZoneHandle(Z, Smi::New(cid)));
+    return;
   }
   SetValue(instr, non_constant_);
 }
 
 void ConstantPropagator::VisitLoadField(LoadFieldInstr* instr) {
   Value* instance = instr->instance();
   if ((instr->recognized_kind() == MethodRecognizer::kObjectArrayLength) &&
       instance->definition()->OriginalDefinition()->IsCreateArray()) {
     Value* num_elements = instance->definition()
                               ->OriginalDefinition()
@@ skipping 828 matching lines @@
 
   if (FLAG_trace_constant_propagation &&
       FlowGraphPrinter::ShouldPrint(graph_->function())) {
     FlowGraphPrinter::PrintGraph("After CP", graph_);
   }
 }
 
 }  // namespace dart
 
 #endif  // !defined(DART_PRECOMPILED_RUNTIME)