Move Persistent Mode Optimization away from firstEffect

Persistent mode needs to clone a parent and add its children if a child has
changed.

We have an optimization in persistent mode where we don't do that if no
child could've changed. If there are no effects scheduled for any child
then there couldn't have been changes.

Instead of checking for this on firstEffect, we now check this on the
children's effectTag and subtreeTags.

This is quite unfortunate because if we could just do this check a little
bit later we would've already gotten it transferred to the completed work's
subtreeTag. Now we have to loop over all the children and if any of them
changed, we have to loop over them again. Doing at least two loops per
parent.

Author: sebmarkbage

packages/react-reconciler/src/ReactFiberCompleteWork.new.js

@@ -65,7 +65,9 @@ import {
   NoEffect,
   DidCapture,
   Snapshot,
+  MutationMask,
 } from './ReactSideEffectTags';
+import {NoEffect as NoSubtreeTag, Mutation} from './ReactSubtreeTags';
 import invariant from 'shared/invariant';
 
 import {
@@ -154,6 +156,25 @@ function markRef(workInProgress: Fiber) {
   workInProgress.effectTag |= Ref;
 }
 
+function hadNoMutationsEffects(current: null | Fiber, completedWork: Fiber) {
+  const didBailout = current !== null && current.child === completedWork.child;
+  if (didBailout) {
+    return true;
+  }
+
+  let child = completedWork.child;
+  while (child !== null) {
+    if ((child.effectTag & MutationMask) !== NoEffect) {
+      return false;
+    }
+    if ((child.subtreeTag & Mutation) !== NoSubtreeTag) {
+      return false;
+    }
+    child = child.sibling;
+  }
+  return true;
+}
+
 let appendAllChildren;
 let updateHostContainer;
 let updateHostComponent;
@@ -198,7 +219,7 @@ if (supportsMutation) {
     }
   };
 
-  updateHostContainer = function(workInProgress: Fiber) {
+  updateHostContainer = function(current: null | Fiber, workInProgress: Fiber) {
     // Noop
   };
   updateHostComponent = function(
@@ -442,13 +463,13 @@ if (supportsMutation) {
       node = node.sibling;
     }
   };
-  updateHostContainer = function(workInProgress: Fiber) {
+  updateHostContainer = function(current: null | Fiber, workInProgress: Fiber) {
     const portalOrRoot: {
       containerInfo: Container,
       pendingChildren: ChildSet,
       ...
     } = workInProgress.stateNode;
-    const childrenUnchanged = workInProgress.firstEffect === null;
+    const childrenUnchanged = hadNoMutationsEffects(current, workInProgress);
     if (childrenUnchanged) {
       // No changes, just reuse the existing instance.
     } else {
@@ -473,7 +494,7 @@ if (supportsMutation) {
     const oldProps = current.memoizedProps;
     // If there are no effects associated with this node, then none of our children had any updates.
     // This guarantees that we can reuse all of them.
-    const childrenUnchanged = workInProgress.firstEffect === null;
+    const childrenUnchanged = hadNoMutationsEffects(current, workInProgress);
     if (childrenUnchanged && oldProps === newProps) {
       // No changes, just reuse the existing instance.
       // Note that this might release a previous clone.
@@ -556,7 +577,7 @@ if (supportsMutation) {
   };
 } else {
   // No host operations
-  updateHostContainer = function(workInProgress: Fiber) {
+  updateHostContainer = function(current: null | Fiber, workInProgress: Fiber) {
     // Noop
   };
   updateHostComponent = function(
@@ -700,7 +721,7 @@ function completeWork(
           workInProgress.effectTag |= Snapshot;
         }
       }
-      updateHostContainer(workInProgress);
+      updateHostContainer(current, workInProgress);
       return null;
     }
     case HostComponent: {
@@ -979,7 +1000,7 @@ function completeWork(
     }
     case HostPortal:
       popHostContainer(workInProgress);
-      updateHostContainer(workInProgress);
+      updateHostContainer(current, workInProgress);
       if (current === null) {
         preparePortalMount(workInProgress.stateNode.containerInfo);
       }