[turbofan] General consolidation of element access.

src/compiler/access-info.cc

Index: src/compiler/access-info.cc
diff --git a/src/compiler/access-info.cc b/src/compiler/access-info.cc
index bbbf726773d052e0e77ce2716baebca2b871deb1..3862d86421bd8c622b939ddb1fe1e1a4e1391a6b 100644
--- a/src/compiler/access-info.cc
+++ b/src/compiler/access-info.cc
@@ -206,16 +206,20 @@ bool AccessInfoFactory::ComputeElementAccessInfo(
 bool AccessInfoFactory::ComputeElementAccessInfos(
     MapHandleList const& maps, AccessMode access_mode,
     ZoneVector<ElementAccessInfo>* access_infos) {
-  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;
-    }
+  // 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.
+  //
+  // Similarly, for polymorphic stores of compatible elements kind that
+  // differ only in holeyness, always use the "holey case" code without a
+  // transition. This is beneficial, because CheckMaps can often be optimized
+  // whereas TransitionElementsKind can block optimizations. And as above, we
+  // avoid mutation of the array (we still mutate the array contents).
+  ElementAccessInfo access_info;
+  if (ConsolidateElementAccess(maps, access_mode, &access_info)) {
+    access_infos->push_back(access_info);
+    return true;
   }
 
   // Collect possible transition targets.
@@ -475,32 +479,9 @@ bool AccessInfoFactory::ComputePropertyAccessInfos(
   return true;
 }
 
-namespace {
-
-Maybe<ElementsKind> GeneralizeElementsKind(ElementsKind this_kind,
-                                           ElementsKind that_kind) {
-  if (IsHoleyElementsKind(this_kind)) {
-    that_kind = GetHoleyElementsKind(that_kind);
-  } else if (IsHoleyElementsKind(that_kind)) {
-    this_kind = GetHoleyElementsKind(this_kind);
-  }
-  if (this_kind == that_kind) return Just(this_kind);
-  if (IsFastDoubleElementsKind(that_kind) ==
-      IsFastDoubleElementsKind(this_kind)) {
-    if (IsMoreGeneralElementsKindTransition(that_kind, this_kind)) {
-      return Just(this_kind);
-    }
-    if (IsMoreGeneralElementsKindTransition(this_kind, that_kind)) {
-      return Just(that_kind);
-    }
-  }
-  return Nothing<ElementsKind>();
-}
-
-}  // namespace
-
-bool AccessInfoFactory::ConsolidateElementLoad(MapHandleList const& maps,
-                                               ElementAccessInfo* access_info) {
+bool AccessInfoFactory::ConsolidateElementAccess(
+    MapHandleList const& maps, AccessMode access_mode,
+    ElementAccessInfo* access_info) {
   if (maps.is_empty()) return false;
   InstanceType instance_type = maps.first()->instance_type();
   ElementsKind elements_kind = maps.first()->elements_kind();
@@ -510,9 +491,24 @@ bool AccessInfoFactory::ConsolidateElementLoad(MapHandleList const& maps,
     if (!CanInlineElementAccess(map) || map->instance_type() != instance_type) {
       return false;
     }
-    if (!GeneralizeElementsKind(elements_kind, map->elements_kind())
-             .To(&elements_kind)) {
-      return false;
+    ElementsKind other_kind = map->elements_kind();
+    if (IsHoleyElementsKind(elements_kind)) {
+      other_kind = GetHoleyElementsKind(other_kind);
+    } else if (IsHoleyElementsKind(other_kind)) {
+      elements_kind = GetHoleyElementsKind(elements_kind);
+    }
+    if (elements_kind != other_kind) {
+      if (access_mode != AccessMode::kLoad) return false;
+      if (IsFastDoubleElementsKind(elements_kind) !=
+          IsFastDoubleElementsKind(other_kind)) {
+        return false;
+      }
+      if (IsMoreGeneralElementsKindTransition(elements_kind, other_kind)) {
+        elements_kind = other_kind;
+      } else if (!IsMoreGeneralElementsKindTransition(other_kind,
+                                                      elements_kind)) {
+        return false;
+      }
     }
     receiver_maps[i] = map;
   }