VM: Constant fold more loads from constants in the optimizer.

runtime/vm/constant_propagator.cc

Index: runtime/vm/constant_propagator.cc
diff --git a/runtime/vm/constant_propagator.cc b/runtime/vm/constant_propagator.cc
index 7aa02f1e376ba6a70f2ee5eb4a0ef7595a7620bc..2792f822b99d715c8089b47f203dcbfac2addc27 100644
--- a/runtime/vm/constant_propagator.cc
+++ b/runtime/vm/constant_propagator.cc
@@ -831,30 +831,33 @@ void ConstantPropagator::VisitLoadField(LoadFieldInstr* instr) {
     }
   }
 
-  if (instr->IsImmutableLengthLoad()) {
-    ConstantInstr* constant =
-        instance->definition()->OriginalDefinition()->AsConstant();
-    if (constant != NULL) {
-      if (constant->value().IsString()) {
+  const Object& constant = instance->definition()->constant_value();
+  if (IsConstant(constant)) {
+    if (instr->IsImmutableLengthLoad()) {
+      if (constant.IsString()) {
         SetValue(instr,
-                 Smi::ZoneHandle(
-                     Z, Smi::New(String::Cast(constant->value()).Length())));
+                 Smi::ZoneHandle(Z, Smi::New(String::Cast(constant).Length())));
         return;
       }
-      if (constant->value().IsArray()) {
+      if (constant.IsArray()) {
         SetValue(instr,
-                 Smi::ZoneHandle(
-                     Z, Smi::New(Array::Cast(constant->value()).Length())));
+                 Smi::ZoneHandle(Z, Smi::New(Array::Cast(constant).Length())));
         return;
       }
-      if (constant->value().IsTypedData()) {
-        SetValue(instr,
-                 Smi::ZoneHandle(
-                     Z, Smi::New(TypedData::Cast(constant->value()).Length())));
+      if (constant.IsTypedData()) {
+        SetValue(instr, Smi::ZoneHandle(
+                            Z, Smi::New(TypedData::Cast(constant).Length())));
+        return;
+      }
+    } else {
+      Object& value = Object::Handle();
+      if (instr->Evaluate(constant, &value)) {
+        SetValue(instr, Object::ZoneHandle(Z, value.raw()));
         return;
       }
     }
   }
+
   SetValue(instr, non_constant_);
 }