Teach LoadOptimizer to interblock multi-indirection redundancies in one pass.

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
diff --git a/runtime/vm/flow_graph_optimizer.cc b/runtime/vm/flow_graph_optimizer.cc
index 3d2d5479bd006545976fbaa3afae9591bfbc201a..d54972523febe22e51d2421d237a71259879af16 100644
--- a/runtime/vm/flow_graph_optimizer.cc
+++ b/runtime/vm/flow_graph_optimizer.cc
@@ -5616,9 +5616,11 @@ class PhiPlaceMoves : public ZoneAllocated {
 class AliasedSet : public ZoneAllocated {
  public:
   AliasedSet(Isolate* isolate,
+             DirectChainedHashMap<PointerKeyValueTrait<Place> >* places_map,
              ZoneGrowableArray<Place*>* places,
              PhiPlaceMoves* phi_moves)
       : isolate_(isolate),
+        places_map_(places_map),
         places_(*places),
         phi_moves_(phi_moves),
         aliases_(5),
@@ -5667,6 +5669,12 @@ class AliasedSet : public ZoneAllocated {
         *killed = GetKilledSet(
             LookupAliasId(places_[instr->place_id()]->ToAlias()));
       }
+    } else if (is_load && (place.kind() != Place::kNone)) {
+      const Place* canonical = LookupCanonical(&place);
+      if ((canonical != NULL) &&
+          (canonical->id() != instr->AsDefinition()->place_id())) {
+        instr->AsDefinition()->set_place_id(canonical->id());
+      }
     }
     return is_store;
   }
@@ -5684,6 +5692,10 @@ class AliasedSet : public ZoneAllocated {
     return places_;
   }
 
+  Place* LookupCanonical(Place* place) const {
+    return places_map_->Lookup(place);
+  }
+
   void PrintSet(BitVector* set) {
     bool comma = false;
     for (BitVector::Iterator it(set);
@@ -6055,6 +6067,8 @@ class AliasedSet : public ZoneAllocated {
 
   Isolate* isolate_;
 
+  DirectChainedHashMap<PointerKeyValueTrait<Place> >* places_map_;
+
   const ZoneGrowableArray<Place*>& places_;
 
   const PhiPlaceMoves* phi_moves_;
@@ -6224,17 +6238,14 @@ static AliasedSet* NumberPlaces(
   PhiPlaceMoves* phi_moves = ComputePhiMoves(map, places);
 
   // Build aliasing sets mapping aliases to loads.
-  return new(isolate) AliasedSet(isolate, places, phi_moves);
+  return new(isolate) AliasedSet(isolate, map, places, phi_moves);
 }
 
 
 class LoadOptimizer : public ValueObject {
  public:
-  LoadOptimizer(FlowGraph* graph,
-                AliasedSet* aliased_set,
-                DirectChainedHashMap<PointerKeyValueTrait<Place> >* map)
+  LoadOptimizer(FlowGraph* graph, AliasedSet* aliased_set)
       : graph_(graph),
-        map_(map),
         aliased_set_(aliased_set),
         in_(graph_->preorder().length()),
         out_(graph_->preorder().length()),
@@ -6280,7 +6291,7 @@ class LoadOptimizer : public ValueObject {
       // as loads from loaded context.
       // TODO(vegorov): renumber newly discovered congruences during the
       // forwarding to forward chains without running whole pass twice.
-      LoadOptimizer load_optimizer(graph, aliased_set, &map);
+      LoadOptimizer load_optimizer(graph, aliased_set);
       return load_optimizer.Optimize();
     }
     return false;
@@ -6350,7 +6361,7 @@ class LoadOptimizer : public ValueObject {
             bool is_load = false, is_store = false;
             Place store_place(instr, &is_load, &is_store);
             ASSERT(!is_load && is_store);
-            Place* place = map_->Lookup(&store_place);
+            Place* place = aliased_set_->LookupCanonical(&store_place);
             if (place != NULL) {
               // Store has a corresponding numbered place that might have a
               // load. Try forwarding stored value to it.