VM: Fix checked mode crash (issue 13831).

runtime/vm/flow_graph_optimizer.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.
 
 #include "vm/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 4137 matching lines @@
   // Host CheckSmi instruction and make this phi smi one.
   Hoist(it, pre_header, current);
 
   // Replace value we are checking with phi's input.
   current->value()->BindTo(phi->InputAt(non_smi_input)->definition());
 
   phi->UpdateType(CompileType::FromCid(kSmiCid));
 }
 
 
+// Load instructions handled by load elimination.
+static bool IsCandidateLoad(Instruction* instr) {
+  return instr->IsLoadField()
+      || instr->IsLoadIndexed()
+      || instr->IsLoadStaticField()
+      || instr->IsCurrentContext();
+}
+
+
 static bool IsLoopInvariantLoad(ZoneGrowableArray<BitVector*>* sets,
                                 intptr_t loop_header_index,
                                 Instruction* instr) {
-  return (sets != NULL) &&
+  return IsCandidateLoad(instr) &&
+      (sets != NULL) &&
       instr->HasPlaceId() &&
       ((*sets)[loop_header_index] != NULL) &&
       (*sets)[loop_header_index]->Contains(instr->place_id());
 }
 
 
 void LICM::Optimize() {
   const ZoneGrowableArray<BlockEntryInstr*>& loop_headers =
       flow_graph()->loop_headers();
 
@@ skipping 2264 matching lines @@
     StoreInstanceFieldInstr* instr) {
   SetValue(instr, instr->value()->definition()->constant_value());
 }
 
 
 void ConstantPropagator::VisitLoadStaticField(LoadStaticFieldInstr* instr) {
   const Field& field = instr->StaticField();
   ASSERT(field.is_static());
   if (field.is_final()) {
     Instance& obj = Instance::Handle(field.value());
+    ASSERT(obj.raw() != Object::sentinel().raw());
+    ASSERT(obj.raw() != Object::transition_sentinel().raw());
     if (obj.IsSmi() || obj.IsOld()) {
       SetValue(instr, obj);
       return;
     }
   }
   SetValue(instr, non_constant_);
 }
 
 
 void ConstantPropagator::VisitStoreStaticField(StoreStaticFieldInstr* instr) {
@@ skipping 1416 matching lines @@
   }
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits.length(); i++) {
     CreateMaterializationAt(exits[i], alloc, alloc->cls(), *fields);
   }
 }
 
 
 }  // namespace dart