Introduce a faster version of the addProperties function (#28969)

## Summary

This PR introduces a faster version of the `addProperties` function.
This new function is basically the `diffProperties` with `prevProps` set
to `null`, propagated constants, and all the unreachable code paths
collapsed.

## How did you test this change?

I've tested this change with [the benchmark
app](https://github.com/react-native-community/RNNewArchitectureApp/tree/new-architecture-benchmarks)
and got ~4.4% improvement in the view creation time.

packages/react-native-renderer/src/ReactNativeAttributePayload.js

@@ -15,6 +15,7 @@ import {
 import isArray from 'shared/isArray';
 
 import {enableEarlyReturnForPropDiffing} from 'shared/ReactFeatureFlags';
+import {enableAddPropertiesFastPath} from 'shared/ReactFeatureFlags';
 
 import type {AttributeConfiguration} from './ReactNativeTypes';
 
@@ -444,6 +445,68 @@ function diffProperties(
   return updatePayload;
 }
 
+function fastAddProperties(
+  updatePayload: null | Object,
+  nextProps: Object,
+  validAttributes: AttributeConfiguration,
+): null | Object {
+  let attributeConfig;
+  let nextProp;
+
+  for (const propKey in nextProps) {
+    nextProp = nextProps[propKey];
+
+    if (nextProp === undefined) {
+      continue;
+    }
+
+    attributeConfig = validAttributes[propKey];
+
+    if (attributeConfig === undefined) {
+      continue;
+    }
+
+    if (typeof nextProp === 'function') {
+      nextProp = (true: any);
+    }
+
+    if (typeof attributeConfig !== 'object') {
+      if (!updatePayload) {
+        updatePayload = ({}: {[string]: $FlowFixMe});
+      }
+      updatePayload[propKey] = nextProp;
+      continue;
+    }
+
+    if (typeof attributeConfig.process === 'function') {
+      if (!updatePayload) {
+        updatePayload = ({}: {[string]: $FlowFixMe});
+      }
+      updatePayload[propKey] = attributeConfig.process(nextProp);
+      continue;
+    }
+
+    if (isArray(nextProp)) {
+      for (let i = 0; i < nextProp.length; i++) {
+        updatePayload = fastAddProperties(
+          updatePayload,
+          nextProp[i],
+          ((attributeConfig: any): AttributeConfiguration),
+        );
+      }
+      continue;
+    }
+
+    updatePayload = fastAddProperties(
+      updatePayload,
+      nextProp,
+      ((attributeConfig: any): AttributeConfiguration),
+    );
+  }
+
+  return updatePayload;
+}
+
 /**
  * addProperties adds all the valid props to the payload after being processed.
  */
@@ -452,8 +515,11 @@ function addProperties(
   props: Object,
   validAttributes: AttributeConfiguration,
 ): null | Object {
-  // TODO: Fast path
-  return diffProperties(updatePayload, emptyObject, props, validAttributes);
+  if (enableAddPropertiesFastPath) {
+    return fastAddProperties(updatePayload, props, validAttributes);
+  } else {
+    return diffProperties(updatePayload, emptyObject, props, validAttributes);
+  }
 }
 
 /**

packages/shared/ReactFeatureFlags.js

@@ -123,6 +123,8 @@ export const enableServerComponentLogs = __EXPERIMENTAL__;
 
 export const enableEarlyReturnForPropDiffing = false;
 
+export const enableAddPropertiesFastPath = false;
+
 /**
  * Enables an expiration time for retry lanes to avoid starvation.
  */

packages/shared/forks/ReactFeatureFlags.native-fb-dynamic.js

@@ -29,3 +29,4 @@ export const enableUnifiedSyncLane = __VARIANT__;
 export const passChildrenWhenCloningPersistedNodes = __VARIANT__;
 export const useModernStrictMode = __VARIANT__;
 export const disableDefaultPropsExceptForClasses = __VARIANT__;
+export const enableAddPropertiesFastPath = __VARIANT__;

packages/shared/forks/ReactFeatureFlags.native-fb.js

@@ -31,6 +31,7 @@ export const {
   passChildrenWhenCloningPersistedNodes,
   useModernStrictMode,
   disableDefaultPropsExceptForClasses,
+  enableAddPropertiesFastPath,
 } = dynamicFlags;
 
 // The rest of the flags are static for better dead code elimination.

packages/shared/forks/ReactFeatureFlags.native-oss.js

@@ -103,6 +103,7 @@ export const enableDO_NOT_USE_disableStrictPassiveEffect = false;
 export const passChildrenWhenCloningPersistedNodes = false;
 export const enableEarlyReturnForPropDiffing = false;
 export const enableAsyncIterableChildren = false;
+export const enableAddPropertiesFastPath = false;
 
 export const renameElementSymbol = true;
 

packages/shared/forks/ReactFeatureFlags.test-renderer.js

@@ -78,6 +78,7 @@ export const enableServerComponentKeys = true;
 export const enableServerComponentLogs = true;
 export const enableInfiniteRenderLoopDetection = false;
 export const enableEarlyReturnForPropDiffing = false;
+export const enableAddPropertiesFastPath = false;
 
 export const renameElementSymbol = true;
 

packages/shared/forks/ReactFeatureFlags.test-renderer.native-fb.js

@@ -89,6 +89,7 @@ export const disableDOMTestUtils = false;
 
 export const disableDefaultPropsExceptForClasses = false;
 export const enableEarlyReturnForPropDiffing = false;
+export const enableAddPropertiesFastPath = false;
 
 export const renameElementSymbol = false;
 

packages/shared/forks/ReactFeatureFlags.test-renderer.www.js

@@ -89,6 +89,7 @@ export const disableDOMTestUtils = false;
 
 export const disableDefaultPropsExceptForClasses = false;
 export const enableEarlyReturnForPropDiffing = false;
+export const enableAddPropertiesFastPath = false;
 
 export const renameElementSymbol = false;
 

packages/shared/forks/ReactFeatureFlags.www-dynamic.js

@@ -31,6 +31,7 @@ export const enableNoCloningMemoCache = __VARIANT__;
 export const retryLaneExpirationMs = 5000;
 export const syncLaneExpirationMs = 250;
 export const transitionLaneExpirationMs = 5000;
+export const enableAddPropertiesFastPath = __VARIANT__;
 
 // Enable this flag to help with concurrent mode debugging.
 // It logs information to the console about React scheduling, rendering, and commit phases.

packages/shared/forks/ReactFeatureFlags.www.js

@@ -35,6 +35,7 @@ export const {
   favorSafetyOverHydrationPerf,
   disableDefaultPropsExceptForClasses,
   enableNoCloningMemoCache,
+  enableAddPropertiesFastPath,
 } = dynamicFeatureFlags;
 
 // On WWW, __EXPERIMENTAL__ is used for a new modern build.