Bug fix in load elimination, constant propagation for LoadClassId.

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
===================================================================
--- runtime/vm/flow_graph_optimizer.cc	(revision 28090)
+++ runtime/vm/flow_graph_optimizer.cc	(working copy)
@@ -4148,7 +4148,7 @@
     switch (instr->tag()) {
       case Instruction::kLoadField: {
         LoadFieldInstr* load_field = instr->AsLoadField();
-        instance_ = load_field->instance()->definition();
+        instance_ = Unwrap(load_field->instance()->definition());
         if (load_field->field() != NULL) {
           kind_ = kField;
           field_ = load_field->field();
@@ -4164,7 +4164,7 @@
         StoreInstanceFieldInstr* store_instance_field =
             instr->AsStoreInstanceField();
         kind_ = kField;
-        instance_ = store_instance_field->instance()->definition();
+        instance_ = Unwrap(store_instance_field->instance()->definition());
         field_ = &store_instance_field->field();
         break;
       }
@@ -4172,7 +4172,7 @@
       case Instruction::kStoreVMField: {
         StoreVMFieldInstr* store_vm_field = instr->AsStoreVMField();
         kind_ = kVMField;
-        instance_ = store_vm_field->dest()->definition();
+        instance_ = Unwrap(store_vm_field->dest()->definition());
         offset_in_bytes_ = store_vm_field->offset_in_bytes();
         break;
       }
@@ -4191,7 +4191,7 @@
       case Instruction::kLoadIndexed: {
         LoadIndexedInstr* load_indexed = instr->AsLoadIndexed();
         kind_ = kIndexed;
-        instance_ = load_indexed->array()->definition();
+        instance_ = Unwrap(load_indexed->array()->definition());
         index_ = load_indexed->index()->definition();
         *is_load = true;
         break;
@@ -4200,7 +4200,7 @@
       case Instruction::kStoreIndexed: {
         StoreIndexedInstr* store_indexed = instr->AsStoreIndexed();
         kind_ = kIndexed;
-        instance_ = store_indexed->array()->definition();
+        instance_ = Unwrap(store_indexed->array()->definition());
         index_ = store_indexed->index()->definition();
         break;
       }
@@ -4231,7 +4231,7 @@
 
   void set_instance(Definition* def) {
     ASSERT((kind_ == kField) || (kind_ == kVMField) || (kind_ == kIndexed));
-    instance_ = def;
+    instance_ = Unwrap(def);
   }
 
   const Field& field() const {
@@ -4302,6 +4302,13 @@
   static Place* Wrap(const Place& place);
 
  private:
+  static Definition* Unwrap(Definition* defn) {

[Kevin Millikin (Google), 2013/10/02 12:36:19]

Even though it's only used locally, this name is too generic.  Try something
snazzy like OriginalDefinitionOf or RealDefinitionOf.

[Florian Schneider, 2013/10/02 12:58:41]

Done.

+    while (defn->IsRedefinition()) {
+      defn = defn->AsRedefinition()->value()->definition();
+    }
+    return defn;
+  }
+
   bool SameField(Place* other) const {
     return (kind_ == kField) ? (field().raw() == other->field().raw())
                              : (offset_in_bytes_ == other->offset_in_bytes_);
@@ -6280,6 +6287,11 @@
 
 
 void ConstantPropagator::VisitLoadClassId(LoadClassIdInstr* instr) {
+  intptr_t cid = instr->object()->Type()->ToCid();
+  if (cid != kDynamicCid) {
+    SetValue(instr, Smi::ZoneHandle(Smi::New(cid)));
+    return;
+  }
   SetValue(instr, non_constant_);

[Kevin Millikin (Google), 2013/10/02 12:36:19]

You could also try this: if instr->object() has a constant value that is an
instance (I guess it should be), then set this instruction's constant value to
that one's class ID.

[Florian Schneider, 2013/10/02 12:58:41]

Done.

 }