[turbofan] Improve caching in escape analysis.

src/compiler/escape-analysis.h

Index: src/compiler/escape-analysis.h
diff --git a/src/compiler/escape-analysis.h b/src/compiler/escape-analysis.h
index c40684bb31c1f7312904b87f56e85502a18dfc0d..25c2dbd7fbd78eff9cc3828dd94e94097e6134c3 100644
--- a/src/compiler/escape-analysis.h
+++ b/src/compiler/escape-analysis.h
@@ -76,28 +76,8 @@ class EscapeStatusAnalysis {
 DEFINE_OPERATORS_FOR_FLAGS(EscapeStatusAnalysis::EscapeStatusFlags)
 
 
-class MergeCache {
- public:
-  explicit MergeCache(Zone* zone)
-      : states_(zone), objects_(zone), fields_(zone) {
-    states_.reserve(4);
-    objects_.reserve(4);
-    fields_.reserve(4);
-  }
-  ZoneVector<VirtualState*>& states() { return states_; }
-  ZoneVector<VirtualObject*>& objects() { return objects_; }
-  ZoneVector<Node*>& fields() { return fields_; }
-  void Clear() {
-    states_.clear();
-    objects_.clear();
-    fields_.clear();
-  }
-
- private:
-  ZoneVector<VirtualState*> states_;
-  ZoneVector<VirtualObject*> objects_;
-  ZoneVector<Node*> fields_;
-};
+// Forward Declaration.
+class MergeCache;
 
 
 // EscapeObjectAnalysis simulates stores to determine values of loads if
@@ -161,7 +141,7 @@ class EscapeAnalysis {
   ZoneVector<VirtualState*> virtual_states_;
   ZoneVector<Node*> replacements_;
   EscapeStatusAnalysis escape_status_;
-  MergeCache cache_;
+  MergeCache* cache_;
 
   DISALLOW_COPY_AND_ASSIGN(EscapeAnalysis);
 };