[turbofan] Refactor ComputeElementAccessInfos

... such that the feedback maps can evenentually be processed in the
serialization phase.

Bug: v8:7790
Change-Id: Ic033e88646a1b161710b1ca2028ef10f49d23cfd
Reviewed-on: https://chromium-review.googlesource.com/c/1472293Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59592}

src/compiler/access-info.cc

@@ -271,20 +271,14 @@ bool AccessInfoFactory::ComputeElementAccessInfo(
   return true;
 }
 
-bool AccessInfoFactory::ComputeElementAccessInfos(
-    MapHandles const& maps, AccessMode access_mode,
-    ZoneVector<ElementAccessInfo>* access_infos) const {
-  if (access_mode == AccessMode::kLoad) {
-    // For polymorphic loads of similar elements kinds (i.e. all tagged or all
-    // double), always use the "worst case" code without a transition.  This is
-    // much faster than transitioning the elements to the worst case, trading a
-    // TransitionElementsKind for a CheckMaps, avoiding mutation of the array.
-    ElementAccessInfo access_info;
-    if (ConsolidateElementLoad(maps, &access_info)) {
-      access_infos->push_back(access_info);
-      return true;
-    }
-  }
+typedef std::vector<std::pair<Handle<Map>, Handle<Map>>> TransitionList;
+
+namespace {
+void ProcessFeedbackMaps(Isolate* isolate, MapHandles const& maps,
+                         MapHandles* receiver_maps,
+                         TransitionList* transitions) {
+  DCHECK(receiver_maps->empty());
+  DCHECK(transitions->empty());
 
   // Collect possible transition targets.
   MapHandles possible_transition_targets;
@@ -298,23 +292,40 @@ bool AccessInfoFactory::ComputeElementAccessInfos(
   }
 
   // Separate the actual receiver maps and the possible transition sources.
-  MapHandles receiver_maps;
-  receiver_maps.reserve(maps.size());
-  std::vector<std::pair<Handle<Map>, Handle<Map>>> transitions(maps.size());
   for (Handle<Map> map : maps) {
     // Don't generate elements kind transitions from stable maps.
     Map transition_target = map->is_stable()
                                 ? Map()
                                 : map->FindElementsKindTransitionedMap(
-                                      isolate(), possible_transition_targets);
+                                      isolate, possible_transition_targets);
     if (transition_target.is_null()) {
-      receiver_maps.push_back(map);
+      receiver_maps->push_back(map);
     } else {
-      transitions.push_back(
-          std::make_pair(map, handle(transition_target, isolate())));
+      transitions->emplace_back(map, handle(transition_target, isolate));
+    }
+  }
+}
+}  // namespace
+
+bool AccessInfoFactory::ComputeElementAccessInfos(
+    MapHandles const& maps, AccessMode access_mode,
+    ZoneVector<ElementAccessInfo>* access_infos) const {
+  if (access_mode == AccessMode::kLoad) {
+    // For polymorphic loads of similar elements kinds (i.e. all tagged or all
+    // double), always use the "worst case" code without a transition.  This is
+    // much faster than transitioning the elements to the worst case, trading a
+    // TransitionElementsKind for a CheckMaps, avoiding mutation of the array.
+    ElementAccessInfo access_info;
+    if (ConsolidateElementLoad(maps, &access_info)) {
+      access_infos->push_back(access_info);
+      return true;
     }
   }
 
+  MapHandles receiver_maps;
+  TransitionList transitions;
+  ProcessFeedbackMaps(isolate(), maps, &receiver_maps, &transitions);
+
   for (Handle<Map> receiver_map : receiver_maps) {
     // Compute the element access information.
     ElementAccessInfo access_info;