Better constant folding of length-loads in checked mode.

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/cpu.h"
 #include "vm/dart_entry.h"
@@ skipping 8220 matching lines @@
   const Object& object = instr->object()->definition()->constant_value();
   if (IsConstant(object)) {
     SetValue(instr, Smi::ZoneHandle(I, Smi::New(object.GetClassId())));
     return;
   }
   SetValue(instr, non_constant_);
 }
 
 
 void ConstantPropagator::VisitLoadField(LoadFieldInstr* instr) {
+  Value* instance = instr->instance();
   if ((instr->recognized_kind() == MethodRecognizer::kObjectArrayLength) &&
-      (instr->instance()->definition()->IsCreateArray())) {
-    Value* num_elements =
-        instr->instance()->definition()->AsCreateArray()->num_elements();
+      instance->definition()->OriginalDefinition()->IsCreateArray()) {
+    Value* num_elements = instance->definition()->OriginalDefinition()
+        ->AsCreateArray()->num_elements();
     if (num_elements->BindsToConstant() &&
         num_elements->BoundConstant().IsSmi()) {
       intptr_t length = Smi::Cast(num_elements->BoundConstant()).Value();
       const Object& result = Smi::ZoneHandle(I, Smi::New(length));
       SetValue(instr, result);
       return;
     }
   }
 
   if (instr->IsImmutableLengthLoad()) {
-    ConstantInstr* constant = instr->instance()->definition()->AsConstant();
+    ConstantInstr* constant =
+        instance->definition()->OriginalDefinition()->AsConstant();
     if (constant != NULL) {
       if (constant->value().IsString()) {
         SetValue(instr, Smi::ZoneHandle(I,
             Smi::New(String::Cast(constant->value()).Length())));
         return;
       }
       if (constant->value().IsArray()) {
         SetValue(instr, Smi::ZoneHandle(I,
             Smi::New(Array::Cast(constant->value()).Length())));
         return;
@@ skipping 1796 matching lines @@
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits_collector_.exits().length(); i++) {
     CreateMaterializationAt(
         exits_collector_.exits()[i], alloc, *slots);
   }
 }
 
 
 }  // namespace dart