[turbofan] Improve caching in escape analysis.

This also fixes a related bug in phi handling.

R=bmeurer@chromium.org
BUG=v8:4586
LOG=n

Review URL: https://codereview.chromium.org/1554073003

Cr-Commit-Position: refs/heads/master@{#33106}

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);
 };