Generalize bounds checks.

runtime/vm/flow_graph.h

Index: runtime/vm/flow_graph.h
diff --git a/runtime/vm/flow_graph.h b/runtime/vm/flow_graph.h
index 45d64a7f8e41b1be53e2418c4eb6ddca97780b8f..cab5bbe245cd1ba70fc1508a6a64ec03727eec68 100644
--- a/runtime/vm/flow_graph.h
+++ b/runtime/vm/flow_graph.h
@@ -5,6 +5,7 @@
 #ifndef VM_FLOW_GRAPH_H_
 #define VM_FLOW_GRAPH_H_
 
+#include "vm/bit_vector.h"
 #include "vm/growable_array.h"
 #include "vm/hash_map.h"
 #include "vm/intermediate_language.h"
@@ -443,6 +444,52 @@ class BlockEffects : public ZoneAllocated {
 };
 
 
+class DefinitionWorklist : public ValueObject {
+ public:
+  DefinitionWorklist(FlowGraph* flow_graph,
+                     intptr_t initial_capacity)
+      : defs_(initial_capacity),
+        contains_vector_(
+            new BitVector(flow_graph->isolate(),
+                          flow_graph->current_ssa_temp_index())) {
+  }
+
+  void Add(Definition* defn) {
+    if (!Contains(defn)) {
+      defs_.Add(defn);
+      contains_vector_->Add(defn->ssa_temp_index());
+    }
+  }
+
+  bool Contains(Definition* defn) const {
+    return (defn->ssa_temp_index() >= 0) &&
+        contains_vector_->Contains(defn->ssa_temp_index());
+  }
+
+  bool IsEmpty() const {
+    return defs_.is_empty();
+  }
+
+  Definition* RemoveLast() {
+    Definition* defn = defs_.RemoveLast();
+    contains_vector_->Remove(defn->ssa_temp_index());
+    return defn;
+  }
+
+  const GrowableArray<Definition*>& definitions() const { return defs_; }
+  BitVector* contains_vector() const { return contains_vector_; }
+
+  void Clear() {
+    defs_.TruncateTo(0);
+    contains_vector_->Clear();
+  }
+
+ private:
+  GrowableArray<Definition*> defs_;
+  BitVector* contains_vector_;
+};
+
+
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_H_